U.S. patent number RE39,339 [Application Number 09/390,583] was granted by the patent office on 2006-10-17 for compositions for manufacturing fiber-reinforced, starch-bound articles having a foamed cellular matrix.
This patent grant is currently assigned to E. Khashoggi Industries, LLC. Invention is credited to Per Just Andersen, Simon K. Hodson.
United States Patent |
RE39,339 |
Andersen , et al. |
October 17, 2006 |
Compositions for manufacturing fiber-reinforced, starch-bound
articles having a foamed cellular matrix
Abstract
Compositions, methods, and systems for manufacturing articles,
particularly containers and packaging materials, having a
fiber-reinforced, starch-bound cellular matrix. Suitable mixtures
used to form the articles are prepared by first preparing a viscous
preblended mixture comprising water, a gelatinized starch-based
binder, and fibers having an average length greater than about 2
mm. The highly viscous preblended mixture effectively transfers the
shearing forces of the mixer to the fibers. The final moldable
mixture is then prepared by mixing into the preblended mixture the
remaining starch-based binder, water, and other desired admixtures,
e.g., mold-releasing agents, inorganic filler rheology-modifying
agents, plasticizers, coating materials, and dispersants, in the
correct proportions to form an article which has the desired
performance criteria. The moldable mixtures are heated between
molds at an elevated temperature and pressure to produce
form-stable articles having a desired shape and a selectively
controlled foamed structural matrix. The articles may be
manufactured to have properties substantially similar to articles
presently made from conventional materials like paper, paperboard,
polystyrene, plastic, or other organic-based materials and have
especial utility in the mass-production of containers, particularly
food and beverage containers.
Inventors: |
Andersen; Per Just (Santa
Barbara, CA), Hodson; Simon K. (Santa Barbara, CA) |
Assignee: |
E. Khashoggi Industries, LLC
(Santa Barbara, CA)
|
Family
ID: |
37086110 |
Appl.
No.: |
09/390,583 |
Filed: |
September 2, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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08288664 |
Aug 9, 1994 |
5660900 |
|
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|
08288667 |
Aug 9, 1994 |
5783126 |
|
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|
08218971 |
Mar 25, 1994 |
5830305 |
|
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|
08109100 |
Aug 18, 1993 |
|
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|
08095662 |
Jul 21, 1993 |
5385764 |
|
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|
07982383 |
Nov 25, 1992 |
|
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|
07929898 |
Aug 11, 1992 |
|
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|
07929898 |
Aug 11, 1992 |
|
|
|
Reissue of: |
08327524 |
Oct 21, 1994 |
05662731 |
Sep 2, 1997 |
|
|
Current U.S.
Class: |
106/206.1;
206/524.7; 206/524.3; 106/400; 428/220; 428/317.9; 428/318.8;
428/319.9; 428/34.5; 428/35.6; 428/35.7; 428/36.4; 521/68;
521/84.1; 523/128; 536/102; 536/107; 428/319.3; 428/318.4;
428/297.4; 106/217.01 |
Current CPC
Class: |
Y02W
90/11 (20150501); Y02W 90/10 (20150501) |
Current International
Class: |
C04B
14/38 (20060101) |
Field of
Search: |
;428/318.4,318.8,319.3-319.9,34.5,35.6,35.7,36.4,220,297.4,317.9,532
;156/324 ;206/524.3,524.7 ;106/206.1,207.01,400 ;521/68,84.1
;536/102,107 ;523/128 |
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|
Primary Examiner: Vo; Hai
Attorney, Agent or Firm: Workman Nydegger
Parent Case Text
This application is a continuation-in-part of U.S. Ser. No.
08/288,664, filed Aug. 9, 1994, now allowed, and a
continuation-in-part of U.S. Ser. No. 08/288,667, filed Aug. 9,
1994, pending U.S. Ser. No. 08/288,667 is a continuation-in-part of
U.S. Ser. No. 08/218,971, filed Mar. 25, 1994, pending, and a
continuation-in-part of U.S. Ser. No. 08/109,100, filed Aug. 18,
1993, now abandoned, and a continuation-in-part of U.S. Ser. No.
08/095,662, filed Jul. 21, 1993, now U.S. Pat. No. 5,385,764, and a
continuation-in-part of U.S. Ser. No. 07/982,383, filed Nov. 25,
1992, now abandoned, and a continuation-in-part of U.S. Ser. No.
07/929,898, filed Aug. 11, 1992, now abandoned. U.S. Ser. No.
08/288,664 is a continuation-in-part of U.S. Ser. No. 07/928,898,
filed Aug. 11, 1992, now abandoned. .Iadd.For purposes of
disclosure of the present invention, each of the foregoing
applications is incorporated herein by specific reference.
.Iaddend.
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
.[.1. A starch-based composition for molding into an article having
a starch-bound cellular matrix, the starch-based composition
comprising water, a starch-based binder in a concentration greater
than about 20% by weight of the starch-based composition, and a
fibrous material having an average fiber length greater than about
2 mm and an aspect ratio greater than about 10:1, wherein the
fibers are substantially homogeneously dispersed throughout the
starch-based compositions, wherein the starch-based binder includes
a substantially ungelatinized component comprising unmodified
starch granules in an amount in a range from about 50% to about 90%
by weight of the starch-based binder and a substantially
gelatinized component comprising gelatinized starch in an amount in
a range from about 10% to about 50% by weight of the starch-based
binder prior to molding the composition into the article..].
.[.2. A composition as defined in claim 1, wherein the starch-based
binder includes a potato starch or a waxy corn starch..].
.[.3. A composition as defined in claim 1, wherein the starch-based
binder includes a plurality of different kinds of starches..].
.[.4. A composition as defined in claim 1, wherein the starch-based
binder is included in an mount in a range from about 20% to about
80% by weight of total solids..].
.[.5. A composition as defined in claim 1, wherein the starch-based
binder is included in an amount in a range from about 40% to about
60% by weight of the total solids..].
.[.6. A composition as defined in claim 1, wherein the fibrous
material is selected from the group consisting of natural cellulose
fibers, glass fibers, synthetic polymer fibers, and mixtures
thereof..].
.[.7. A composition as defined in claim 1, wherein the fibers have
an average diameter in a range from about 10 .mu.m to about 50
.mu.m..].
.[.8. A composition as defined in claim 1, wherein the fibrous
material is included in an amount in a range from about 1% to about
20% by weight of total solids..].
.[.9. A composition as defined in claim 1, further including an
inorganic aggregate selected from the group consisting of calcium
carbonate, perlite, zeolites, vermiculite, sandstone, glass beads,
aerogel, mica, clay, kaolin, gravel, exfoliated rock, derivatives
thereof, and mixtures thereof..].
.[.10. A composition as defined in claim 9, wherein the inorganic
aggregate is included in an mount in a range from about 20% to
about 80% by weight of the starch-based composition..].
.[.11. A composition as defined in claim 9, wherein the inorganic
aggregate includes individual particles having a plurality of
different sizes..].
.[.12. A composition as defined in claim 11, wherein the sizes of
the individual particles are selected to maximize the natural
packing density of the inorganic aggregate within the starch-based
composition..].
.[.13. A composition as defined in claim 12, wherein the sizes of
the individual particles are selected so that the natural packing
density of the inorganic aggregate is in a range from about 0.5 to
about 0.9..].
.[.14. A composition as defined in claim 9, wherein the inorganic
aggregate has a specific surface area in a range from about 0.1
m.sup.2/g to about 50 m.sup.2/g..].
.[.15. A composition ad defined in claim 9, wherein the inorganic
aggregate has a specific surface area in a range from about 0.2
m.sup.2/g to about 2 m.sup.2/g..].
.[.16. A composition as defined in claim 9, wherein the inorganic
aggregate is included in an amount sufficient to yield an article
having a specific heat in a range from about 0.1 J/gK to about 400
J/gK at 20.degree. C..].
.[.17. A composition as defined in claim 1, wherein the water has a
concentration in a range from about 15% to about 80% by
weight..].
.[.18. A composition as defined in claim 1, having a viscosity
greater than about 10 Pas measured at a shear rate of 1
s.sup.-1..].
.[.19. A composition as defined in claim 1, having a viscosity in a
range from about 50 to about 100 Pas measured at a shear rate of 1
s.sup.-1..].
.[.20. A composition as defined in claim 1, having a viscosity in a
range from about 200 to about 500 Pas measured at a shear rate of 1
s.sup.-1. .].
.[.21. A composition as defined in claim 1, wherein the average
fiber length is greater than about 4 mm..].
.[.22. A composition as defined in claim 1, wherein the average
fiber length is greater than about 8 mm..].
.[.23. An inorganically filled starch-based composition for molding
into an article, the composition comprising: (a) a starch-based
binder in a concentration greater than about 20% by weight of the
starch-based composition, the starch-based binder including a
substantially ungelatinized component comprising unmodified starch
granules in an amount in a range from about 50% to about 90% by
weight of the starch-based binder and a substantially gelatinized
component comprising gelatinized starch in an amount in a range
from about 10% to about 50% by weight of the starch-based binder
prior to molding the composition into the article; (b) fibers in a
concentration greater than about 1% by weight of the starch-based
composition and having an average fiber length greater than about 2
mm and an aspect ratio greater than about 10:1, wherein the fibers
are substantially homogeneously dispersed throughout the
starch-based composition; and (c) an inorganic aggregate in a
concentration greater than about 5% by weight of the starch-based
composition..].
.[.24. An inorganically filled starch-based composition as defined
in claim 23, wherein the fibers have a concentration greater than
about 5% by weight of the starch-based composition..].
.[.25. An inorganically filled starch-based composition as defined
in claim 23, wherein the fibers have a concentration greater than
about 10% by weight of the starch-based composition..].
.[.26. An inorganically filled starch-based composition as defined
in claim 23, wherein the average fiber length is greater than about
4 mm..].
.[.27. An inorganically filled starch-based composition as defined
in claim 23, wherein the average fiber length is greater than about
8 mm..].
.[.28. An inorganically filled starch-based composition as defined
in claim 23, wherein the inorganic aggregate is included in an
amount greater than about 15% by weight of the starch-based
composition..].
.[.29. An inorganically filled starch-based composition as defined
in claim 23, wherein the inorganic aggregate is included in an
amount greater than about 30% by weight of the starch-based
composition..].
.[.30. A starch-based composition for forming an article of
manufacture having a foamed structural matrix, the composition
comprising: (a) a starch-based binder having a concentration of
about 20% to about 80% by weight of solids within the starch-based
composition; (b) an inorganic aggregate having a concentration of
about 0% to about 80% by weight of solids within the starch-based
composition; (c) a fibrous material having a concentration of about
2% to about 50% by weight of solids within the starch-based
composition, said fibrous material having an average fiber length
greater than about 2 mm and being substantially uniformly dispersed
throughout the starch-based composition; and (d) water having a
concentration of about 15% to about 80% by weight of the
starch-based composition; wherein the starch-based binder includes
a gelatinized component comprising gelatinized starch in an amount
from about 5% to about 70% by weight of the starch-based binder,
and wherein the balance of the starch-based binder comprises an
ungelatinized component comprising ungelatinized, unmodified starch
granules prior to forming the composition into an article, wherein
said gelatinized component aids in the dispersion of the fibrous
material throughout the starch-based composition during
mixing..].
.[.31. A starch-based moldable mixture for forming an article of
manufacture, the moldable mixture comprising water, a starch-based
binder in a concentration greater than about 20% by weight, and a
fibrous material having an average fiber length greater than about
2 mm, and an aspect ratio of at least about 10:1, wherein the
moldable mixture has a viscosity greater than about 10 Pas, wherein
the starch-based binder includes gelatinized component comprising
gelatinized starch in an amount from about 5% to about 70% by
weight of the starch-based binder, and wherein the balance of the
starch-based binder comprises an ungelatinized component comprising
ungelatinized, unmodified starch granules prior to forming the
composition into an article, wherein said gelatinized component
aids in the dispersion of the fibrous material throughout the
starch-based composition during mixing..].
.Iadd.32. A composite composition comprising a first region that
includes a fiber-reinforced starch-based composition and a second
region adjacent to the first region that includes a coating
composition, the composite composition formed by the process
comprising the steps of: providing an aqueous starch-based
composition including water, a starch-based binder in a
concentration greater than about 20% by weight, and a fibrous
material having an aspect ratio of at least about 10:1, wherein the
intermediate composition has a viscosity greater than about 10 Pas,
wherein the starch-based binder includes a gelatinized component
comprising gelatinized starch in an amount from about 5% to about
70% by weight of the starch-based binder, and wherein the balance
of the starch-based binder comprises an ungelatinized component
comprising ungelatinized, unmodified starch granules, wherein the
gelatinized component aids in the dispersion of the fibrous
material throughout the intermediate aqueous starch-based
composition during mixing in order for the fibrous material to
strengthen the starch-based composition; forming the first region
of the starch-based composite composition by heating the aqueous
starch-based composition so as to at least partially gelatinize the
starch granules and so as to also remove at least a portion of the
water by evaporation to thereby cause the starch-based binder to
become at least partially solidified; and forming the second region
of the starch-based composite composition by positioning a coating
composition that is resistant to moisture adjacent to the first
region, wherein the coating composition is formed from at least one
of an edible oil, a drying oil, melamine, an epoxy resin, a terpene
resin, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, a
polyacrylate, hydroxypropylmethylcellulose, methocel, polyethylene
glycol, an acrylic, an acrylic copolymer, polyurethane, polylactic
acid, polyhydroxybutyrate-hydroxyvalerate copolymer, a
biodegradable polyester resin, soybean protein, or a
wax..Iaddend.
.Iadd.33. A composite composition as defined in claim 32, wherein
the fibrous material includes fibers having a length less than
about 25 mm..Iaddend.
.Iadd.34. A composite as defined in claim 32, wherein the fibrous
material includes fibers having a length less than about 1.5
mm..Iaddend.
.Iadd.35. A composite composition as defined in claim 32, wherein
the fibrous material includes fibers having an aspect ratio in a
range from about 40:1 to about 2500:1..Iaddend.
.Iadd.36. A composite composition as defined in claim 32, wherein
the fibers are included in an amount in a range from about 2% to
about 80% by weight of the aqueous starch-based
composition..Iaddend.
.Iadd.37. A composite composition as defined in claim 32, wherein
the aqueous starch-based composition further includes an inorganic
filler included in an amount in a range from about 20% to about 90%
by weight of the aqueous starch-based composition..Iaddend.
.Iadd.38. A composite composition as defined in claim 32, wherein
the first region includes sufficient void spaces so as to have a
density in a range from about 0.05 g/cm.sup.3 to about 1
g/cm.sup.3..Iaddend.
.Iadd.39. A composite composition as defined in claim 32, wherein
the first region includes sufficient void spaces so as to have a
density in a range from about 0.1 g/cm.sup.3 to about 0.5
g/cm.sup.3..Iaddend.
.Iadd.40. A composite composition as defined in claim 32, wherein
the first region includes an exterior skin subregion having a
density and an interior foam subregion adjacent to the exterior
skin subregion having a density that is significantly lower than
the density of the exterior skin subregion..Iaddend.
.Iadd.41. A composite composition as defined in claim 32, wherein
the first region has a cross-sectional thickness in a range of
about 0.5 mm to about 5 mm..Iaddend.
.Iadd.42. A composite composition as defined in claim 32, wherein
the coating composition is initially in liquid form when positioned
adjacent to the first region..Iaddend.
.Iadd.43. A composite composition as defined in claim 32, wherein
the coating composition comprises a laminating
material..Iaddend.
.Iadd.44. A composite composition as defined in claim 32, wherein
the coating composition comprises a substantially uniform
film..Iaddend.
.Iadd.45. A composite composition as defined in claim 32, wherein
the starch-based binder includes at least one of native starch or a
starch derivative..Iaddend.
.Iadd.46. A composite composition comprising a first region that
includes a fiber-reinforced starch-based composition and a second
region adjacent to the first region that includes a laminating
composition, the composite composition formed by the process
comprising the steps of: providing an aqueous starch-based
composition including water, a starch-based binder in a
concentration greater than about 20% by weight, and a fibrous
material having an aspect ratio of at least about 10:1, wherein the
intermediate composition has a viscosity greater than about 10 Pas,
wherein the starch-based binder includes a gelatinized component
comprising gelatinized starch in an amount from about 5% to about
70% by weight of the starch-based binder, and wherein the balance
of the starch-based binder comprises an ungelatinized component
comprising ungelatinized, unmodified starch granules, wherein the
gelatinized component aids in the dispersion of the fibrous
material throughout the intermediate aqueous starch-based
composition during mixing in order for the fibrous material to
strengthen the starch-based composition; forming the first region
of the starch-based composite composition by heating the aqueous
starch-based composition so as to at least partially gelatinize the
starch granules and so as to also remove at least a portion of the
water by evaporation to thereby cause the starch-based binder to
become at least partially solidified; and forming the second region
of the starch-based composite composition by positioning a
substantially solid laminating composition that is resistant to
moisture adjacent to the first region after the starch-based binder
has become at least partially solidified..Iaddend.
.Iadd.47. A composite composition as defined in claim 46, wherein
the laminating composition is formed from a biodegradable polymer
selected from the group consisting of cellulosic ethers, cellulose
acetate, starches, biodegradable polyamides, polyvinyl alcohol,
polyvinyl acetate, polylactic acid,
polyhydroxybutyrate-hydroxyvalerate copolymer, other biodegradable
polyester resins, soybean protein, and mixtures
thereof..Iaddend.
.Iadd.48. A composite composition as defined in claim 46, wherein
the laminating composition comprises a substantially uniform
film..Iaddend.
.Iadd.49. A composite composition as defined in claim 46, wherein
the first region includes an exterior skin subregion having a
density and an interior foam subregion adjacent to the exterior
skin subregion having a density that is significantly lower than
the density of the exterior skin subregion..Iaddend.
.Iadd.50. A composite composition as defined in claim 46, wherein
the starch-based binder includes at least one of native starch or a
starch derivative..Iaddend.
.Iadd.51. A composite composition as defined in claim 46, wherein
the fibrous material includes fibers having a length less than
about 1.5 mm..Iaddend.
.Iadd.52. A composite composition comprising a first region that
includes a fiber-reinforced starch-based composition and a second
region adjacent to the first region that includes a biodegradable
material, the composite composition formed by the process
comprising the steps of: providing an aqueous starch-based
composition including water, a starch-based binder in a
concentration greater than about 20% by weight, and a fibrous
material having an aspect ratio of at least about 10:1, wherein the
intermediate composition has a viscosity greater than about 10 Pas,
wherein the starch-based binder includes a gelatinized component
comprising gelatinized starch in an amount from about 5% to about
70% by weight of the starch-based binder, and wherein the balance
of the starch-based binder comprises an ungelatinized component
comprising ungelatinized, unmodified starch granules, wherein the
gelatinized component aids in the dispersion of the fibrous
material throughout the intermediate aqueous starch-based
composition during mixing in order for the fibrous material to
strengthen the starch-based composition; forming the first region
of the starch-based composite composition by heating the aqueous
starch-based composition so as to at least partially gelatinize the
starch granules and so as to also remove at least a portion of the
water by evaporation to thereby cause the starch-based binder to
become at least partially solidified, wherein the first region
includes an exterior skin subregion having a density and an
interior foam subregion adjacent to the exterior skin subregion
having a density that is significantly lower than the density of
the exterior skin subregion; and forming the second region of the
starch-based composite composition by positioning a biodegradable
material adjacent to the first region, the biodegradable material
being formed from at least one of a biodegradable polyester resin,
polyvinyl alcohol, polyvinyl acetate, polylactic acid, or a
polyhydroxybutyrate-hydroxyvalerate copolymer..Iaddend.
.Iadd.53. A composite composition as defined in claim 52, wherein
the starch-based binder includes at least one of native starch or a
starch derivative..Iaddend.
.Iadd.54. A composite composition as defined in claim 52, wherein
the biodegradable material is initially in liquid form when
positioned adjacent to the first region..Iaddend.
.Iadd.55. A composite composition as defined in claim 52, wherein
the coating composition comprises a laminating
material..Iaddend.
.Iadd.56. A composite composition as defined in claim 52, wherein
the biodegradable material is a substantially uniform
film..Iaddend.
.Iadd.57. A composite composition as defined in claim 52, wherein
the fibrous material includes fibers having a length less than
about 1.5 mm..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved compositions and method
for manufacturing fiber-reinforced, starch-bound articles having a
foamed cellular matrix. More particularly, the present invention
relates to the use of a highly vigorous, preblended mixture in
order to improve the dispersions of long-length fibers (i.e., those
having an average length grater than about 2 mm) into starch-based
mixtures containing well-dispersed fibers from which
environmentally superior containers and other articles or packaging
materials can be economically mass-produced. The inclusion of
long-length fibers reinforces the newly formed starch-bound matrix
so that the articles may be demolded while maintaining enough water
within the foamed matrix so that the articles remain sufficiently
flexible and resilient for the intended use without the need for
conventional conditioning procedures. In addition, the long-length
fibers greatly improve the final strength and toughness of the
starch-bound articles, which allows the manufacture of articles of
reduced cross-section or higher strength to be made. The resultant
articles have a cellular, optionally inorganically-filled,
starch-bound matrix and can be produced less expensively and in a
manner that is environmentally superior to articles manufactured
from conventional materials such as paper, plastic, polystyrene
foam, glass, or metal.
2. The Relevant Technology
A. Conventional Materials
Materials such as paper, paperboard, plastic, polystyrene, and even
metals are presently used in enormous quantity in the manufacture
of articles such as containers, separators, dividers, lids, tops,
cans, and other packaging materials used to protect, store,
package, dispense, or ship an enormous variety of liquid and solid
goods. Containers and other packaging materials protect goods from
environmental influences and distribution damage, particularly from
gases, moisture, light, microorganisms, vermin, physical shock,
crushing forces, vibration, leaking, or spilling. Packaging
materials may also be imprinted with useful or promotional product
information to the consumer, such as the origin of manufacturer,
contents, advertising, instructions, brand identification, and
pricing.
Most conventionally manufactured containers or other packaging
materials (including disposable containers) are made from paper,
paperboard, plastic, polystyrene, glass, or metal materials. Each
year, over 100 billion aluminum cans, billions of glass bottles,
and thousands of tons of paper and plastic are used in storing and
dispensing, e.g., soft drinks, juices, processed foods, cereals,
grains, and beer. In addition, huge quantities of retail goods are
sold or distributed using some sort of packaging material. In the
United States alone, approximately 5.5 million tons of paper made
primarily from tree-derived wood pulp are consumed each year solely
in the production of packaging materials. This vast consumption
represents only about 15% of the total annual domestic paper
productions.
Recently, consciousness-raising organizations have led a debate as
to which of the conventional materials used to make such containers
and other articles (e.g., paper, paperboard, plastic, polystyrene,
glass, or metal) is most damaging to the environment or which is
more environmentally "correct." The debate often misses the point
that each of these materials has its own unique environmental
weaknesses. One faction will frequently tout a particular material
as being superior to another when viewed in light of a particular
environmental problem, while unknowingly (or even knowingly)
ignoring different, often larger, problems associated with the
supposedly "environmentally friendly" material. In reality, the
debate should not be directed to which of these materials is more
or less harmful to the environment, but rather toward asking. Can
we discover or develop an alternative material which will solve
most, if not all, of the various environmental problems associated
with each of these presently used materials?
B. Alternatives Materials
Due to the more recent awareness of the tremendous environmental
impact of using paper, paperboard, plastic, polystyrene, and metals
for a variety of single-use, mainly disposable, articles such as
containers and other packaging materials (not to mention the ever
mounting political pressures), there has been an acute (long since
recognized by those skilled in the art) to find environmentally
superior or improved substitute materials. One creative alternative
has been to manufacture disposable food or beverage containers out
of baked, edible sheets, e.g., waffles or pancakes. Although edible
sheets can be made into trays, cones, and cups that are easily
decomposed, they pose a number of limitations. Edible sheets are
primarily made from a mixture of water, flour, and a rising agent,
which is shaped and baked between heated molds. Fats or oils are
often added to the mixture to assist in the removal of the sheet
from the baking mold. However, oxidation of these fats can cause
the edible sheets to go rancid. From a mechanical standpoint,
edible sheets are generally to brittle and fragile to replace any
but a few of the articles made from conventional materials. This
inherent weakness generally requires the cross-section of the
edible sheet to be substantially increased relative to a similar
article made from conventional materials, thus negating much, if
not all, of the environmental or economic benefits. Furthermore, if
exposed to excessive moisture, the articles can easily grow mold or
decompose prior to or during their intended use, thereby making
such materials unsuitable for many of the amplifications for which
substitution would be desirable.
Other attempts have been made to make articles from renewable
organic materials such as starch. For example, articles have been
made from a mixture of starch, water, and a mold-releasing agent.
The starch-based mixture is baked between heated molds for a period
of 3 minutes or more until the starch gelates, foams, and hardens
by nearly complete drying of the molded starch-based mixture in the
desired shape of the article. The resulting articles, however, were
found to be cost prohibitive. The slow processing times, expensive
equipment, and the relatively high cost of starch compared to
conventional materials made the manufacture of starch-based
articles far more expensive than articles made from conventional
materials. Although inorganic fillers have been added to
starch-based mixtures in an attempt to cut material cost, mixtures
containing any significant portion of fillers have heretofore been
unable to yield structurally sound articles having minimally
required mechanical properties.
In general, such starch-based articles were found to be very
fragile and brittle, particularly when initially demolded, giving
them limited use. This occurred because of the need to drive off
substantially all of the free water within the starch-based
cellular matrix in order to avoid degradation or fracture due to
expansion of the newly demolded article. The starch-based cellular
matrix simply was too soft to be able to withstand the internal
pressures generated by and persisting within the cells due to the
vaporizing free water left within an undercooked article. On the
other hand, baking the articles too long led to carmelization,
fracturing due to shrinkage, and destruction of the binding
capability of the starch material, thereby creating a narrow window
of time in which the starch-based articles could be baked without
yielding a highly defective article.
Moreover, to improve the flexibility and reduce the brittleness of
the starch-bound articles, it was necessary to place the articles
in a conditioning chamber for prolonged periods of time at elevated
humidity and temperature in order for the starch matrix to absorb
adequate levels of moisture. This "conductive step" often took
several minutes, or even hours depending on the processing
conditions, which further retarded the already slow manufacturing
process. Furthermore, the additional processing step of applying a
coating to the article was usually required in order to maintain
the critical level of moisture within the starch-based cellular
matrix of the conditioned articles or make the articles
water-resistant.
Like their edible sheet counterparts, such starch-based articles
suffered from the inability to obtain the requisite materials
properties of conventional materials without greatly increasing the
thickness and mass of the articles manufactured therefrom (with
thicknesses of at least 2 mm, and usually upwards of 5 mm, being
required). Also, they were prone to spoilage if exposed to
excessive moisture, thereby creating a criticality with respect to
moisture: too little and the articles would be too brittle and
fragile to be suitable for their intended use; too much and they
would rot or spoil. Such organic-based articles usually had a poor
surface quality due to poor ventilating, inadequate viscosity, and
nonoptimized flow dynamics, which poor surface was often disguised
by forming them with a waffled surface.
Industry has repeatedly sought to develop more highly inorganically
filled materials capable of being mass-produced into a variety of
disposable articles. Inorganic materials such as clay, natural
minerals, and stone are easily accessed, non-depletable,
inexpensive, and environmentally inert. In spite of economic and
environmental pressures, extensive research, and the associated
long-felt need, the technology simply has not existed for the
economic and feasible production of highly inorganically filled
materials which could be substituted for paper, paperboard,
plastic, polystyrene, metal, or other organic-based articles.
Finally, in an attempt to strengthen the organic-based materials,
such as the aforementioned foamed, starch-based articles, fibers
have been added. Nevertheless, because of the difficulty of
dispersing fibers, particularly longer-length fibers (i.e., those
having an average length greater than about 1.5-2 mm), their
additional has resulted in only small, perhaps insignificant,
increases in the strength or toughness of the resulting foamed,
starch-bound materials. In order to obtain adequate dispersion of
fibers within organic binder solutions it has heretofore been
necessary to subject the fibers to relatively harsh mixing
conditions, such as using a beater as in the breakdown of wood
pulp, and usually by including a relatively large quantity of
water. However, even the addition of large quantities of water in
starch-based materials (up to 80% in some cases) has not resulted
in adequate dispersion of fibers having an average length greater
than about 2 mm. Moreover, the inclusion of a large amount of water
thought to be necessary to disperse the fibers greatly increases
the production costs of the articles because of the tremendous
amount of energy required to remove the excess water from the
formed product.
In addition, in a highly foamed product, the use of fibers having
an average length less than about 1.5 mm is ineffective because the
internal pore diameter averages from 0.25 mm to 1.0 mm, giving an
inadequate anchoring effect to such short fibers (i.e., when the
fiber length is less than 3 times the pore diameter.)
In light of the foregoing, what are needed are novel compositions
and methods for manufacturing novel materials that can replace
paper, paperboard, metal, plastic, polystyrene, or other organic
materials as the material of choice for producing containers and
other articles.
It would be a further improvement in the art to provide
compositions and methods for manufacturing organically-bound
materials that can be formed into containers an other articles
currently made from paper, paperboard, polystyrene, metal, plastic,
or other organic materials.
It would be a tremendous improvement in the art to provide
compositions and methods to improve the dispersion of fibers within
the above organically-bound materials without the use of large
quantities of water. It would yet be a significant improvement if
such compositions and methods allowed for the dispersion of
relatively long-length fibers (i.e., those having an average length
greater than about 1.5-2 mm) within the organically-bound materials
used to make containers or other articles.
It would also be an improvement in the art if the above
organically-bound materials were to include a relatively large
percentage of inorganic aggregate filler, particularly a filler
which is compatible with and commonly found in the earth.
It would be a significant improvement in the art if such
compositions and methods yielded highly inorganically filled,
organically-bound articles that had properties similar, or even
superior, to paper, paperboard, metal, polystyrene, plastic, or
other organic materials.
It would yet be an improvement in the art if such compositions and
methods provided for the manufacture of containers and other
articles without the need for prolonged, high-humidity conditioning
in order to obtain the required flexibility or toughness.
It would be an additional improvement in the art to provide
compositions and methods that yielded starch bound articles that
did not require the application of a coating to maintain adequate
moisture within the cellular matrix or to make the cellular matrix
water resistant.
It would be an additional improvement in the art to provide
compositions and methods for manufacturing highly inorganically
filled, organically-bound materials into containers and other
articles having a smoother, more uniform surface compared to
existing organically-bound articles.
It would also be an improvement in the art if such articles could
be formed using existing manufacturing equipment and techniques
presently used to form such articles from paper, paperboard,
metals, polystyrene, plastic, or other organic materials. It would
further be an improvement if such compositions and methods did not
result in the concomitant generation of wastes involved with the
manufacture of articles from such material.
It would be yet an advancement in the art if such compositions and
methods required the use of less water that had to be removed
during the manufacturing process (as compared to the manufacturer
of paper or other organically-based materials) in order to shorten
the processing time and reduce the initial equipment capital
investment.
From a practical point of view, it would be a significant
improvement if such compositions and methods made possible the
manufacture of containers and other articles at a cost that is
comparable or even superior to existing methods of manufacturing
containers or other articles from paper, paperboard, metal,
plastic, polystyrene, or other organic materials. Specifically, it
would be an advancement in the art if such materials resulted in a
reduction in the consumption of energy, valuable natural resources,
and initial start-up capital presently expended in making articles
from conventional materials, such as paper, metals, polystyrene,
plastic, or other organic materials.
It would further be a significant improvement in the art if such
compositions and methods yielded containers and other articles
having a similar cross-section and comparable mechanical properties
of e.g. insulation, strength, toughness, etc. compared to paper,
paperboard, polystyrene, plastic, or other organic materials.
From a manufacturing perspective, it would be a significant
advancement in the art to provide compositions and methods that
allowed for the mass-production of highly inorganically filled,
organically-bound articles that could be rapidly formed and ready
to use within a matter of minutes from the beginning of the
manufacturing process.
It would also be a tremendous advancement in the art to provide
compositions and methods that allowed for the production of highly
inorganically filled, starch-bound materials having greater
flexibility, flexural strength, toughness, moldability,
mass-producibility, product stability, and lower environmental
impact compared to conventionally manufactured starch-based
materials.
Such compositions and methods, as well as articles made therefrom,
are disclosed and claimed herein.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention is directed to novel compositions and methods
for manufacturing articles having a generally foamed, highly
inorganically filled, fiber-reinforced, organically-bound
structural matrix. Initially, a materials science and
microstructural engineering approach is used to develop and
appropriate particle packed, inorganically filled, moldable mixture
having well-dispersed fibers. The components of the mixture and
their amounts are selected based on an understanding of the
interrelationships between processing parameters and the properties
of the individual components, moldable mixture, and final
article.
The moldable mixture generally includes a starch-based binder, an
inorganic aggregate-filler, well-dispersed fibers, a mold releasing
agent and water to disperse the components, gelate the starch, and
act as an evaporative forming agent. The present invention includes
methods for molding such composition into articles having a foamed
structural matrix. The molding process generally includes forming
the moldable composition between heated dies in order to gelate the
starch-based binder and to cause the water-based solvent to
evaporate, thereby creating a foamed, starch-bound cellular
matrix.
It has been discovered that the long-length fibers dispersed
throughout the moldable mixture and, hence, the final molded
article serve at least two important functions. For and perhaps
most importantly, the fibers reinforce the newly foamed and gelated
starch-bound matrix, so that the molded article can be removed from
the mold while retaining adequate moisture within the structure of
the article to plasticize the starch-bound matrix. This allows the
newly demolded article to have adequate toughness and strength
immediately or shortly after being demolded for its intended
purpose without the need for conventional conditioning, as was
previously required in the manufacture of foamed starch-based
articles. Without the conditioning step to reintroduce moisture
back into the starch-based matrix, foamed starch-based articles,
even those that include quantities of shorter-length fibers, were
usually too brittle and fragile for their intended use. Moreover,
such articles could not simply be demolded without such overdrying
because of the destructive nature of the highly pressurizing water
vapor that otherwise would remain within the cellular structure of
the newly demolded article. The convenient starch-based cellular
matrix alone was simply not strong enough to withstand the internal
buildup of pressure caused by the heated molding process.
Another important benefit of including longer-length fibers within
the molded articles was the dramatic increase in fracture energy,
tensile strength, flexural strength, toughness, flexibility, and
other related properties to their nonfiber or short
fiber-containing counterparts. Because of this, the materials of
the present invention are able to have materials properties similar
or even superior to conventional materials at about the same cross
section or mass. This allows for the manufacture of thinner walled
articles having properties superior to their much thicker-walled,
starch-based counterparts, thereby greatly reducing the mass, cost,
forming time, and environmental impact of the material used to
manufacture such articles. Moreover, the shortened molding times
and the elimination of the previously required conditioning and
coating step greatly reduces the manufacturing costs, both in terms
of labor and energy.
A preferred moldable mixture is formed in two steps. The first step
comprises mixing together the fibers and a portion of the
starch-based binder and water, gelating the starch-based binder to
form a highly viscous, "preblended" mixture, and dispersing the
fibers within the preblended mixture using high shear mixing. The
starch-based binder may be pre-gelated or gelated in situ by
raising the temperature of the preblended mixture to the gelation
temperature of the particular starch-based binder being used. In
the second step, the remaining components are added to the
preblended mixture, such as the remaining ungelated starch-based
binder and water, the mold release agent, the inorganic
component(s), plasticizers, internal coating agents, and any other
desired admixtures.
It has been discovered that in sharp contrast to conventional
practices in which large amounts of water are believed to be
necessary in order to adequately disperse the fibers, thereby
creating a generally low viscosity aqueous slurry, the present
invention exploits the newly discovered ability of the high
viscosity, preblended mixture to transfer shear from the mixer to
the fibers. The inability of conventional practices to obtain
adequate dispersion of fibers within water solvated systems,
particularly fibers having an average length greater than about
1.5-2 mm, is primarily due to the inability of generally low
viscosity mixtures to transfer the shearing force or energy from
the mixer to the fibers. Instead, the energy is dissipated within
the churning aqueous solvent because of the tendency of the
nonviscous water to yield or flow in the direction of the shearing
force without transferring such energy to the fibers or fibrous
clumps. Thus, adding progressively greater amounts of water
generally will not substantially improve the ability of such
mixtures to thoroughly disperse or blend the fibers throughout the
aqueous slurry. Similarly, simply increasing the shear rate or
shear energy of the mixing apparatus does not appreciably improve
the ability to disperse fibers, particularly longer-length fibers.
Moreover, the large amount of excess water must either be removed
or the slurry continuously mixed in order to maintain adequate
dispersion of the fibers within the aqueous suspension.
The present invention solves these problems by creating a
preblended mixture having a high viscosity and yield stress which
it has been discovered is far more effective in directly imparting
the shearing forces of the mixture to the fibers. This is because
the high viscosity and yield stress of the mixture does not allow
for the water solvent to simply dissipate the shearing forces by
the normal churning action of conventional aqueous slurries. The
result is greatly increased dispersion of fibers, particularly
longer-length fibers, compared to conventional methods. In
addition, the highly viscous preblended mixture, as well as the
preferred moldable mixtures discussed below, have sufficient
viscosity to reliably maintain the fibers and other admixtures
thoroughly and evenly dispersed throughout the mixture. The use of
the preblended mixture makes possible the previously unattainable
dispersion of fibers having an average length of at least about 2
mm, and allows for the dispersion of fibers having average fiber
lengths of at least about 3.5 mm, 5 mm, or 10 mm, and even up to
about 25 mm or longer in the case of very strong fibers able to
withstand the increased shearing forces experienced by the longer
fibers.
Once the fibers have been adequately dispersed throughout the
preblended mixture, the moldable mixture is prepared by simply
blending in the remaining components or admixtures. If the
starch-based binder used in the preblended mixture was gelated by
raising the temperature of the preblended mixture to at or above
the gelation temperature, it will usually be preferable to first
cool the mixture to below the gelation temperature before adding
the remainder of the ungelated starch-based binder. Otherwise, the
remaining starch-based binder will gelate prior to the molding
procedure and generally produce inferior articles. It is generally
preferable to maintain the majority of the starch-based binder in a
nongelated state in order to keep the viscosity of the moldable
mixture within the preferred ranges and maintain adequate
flowability and moldability of the moldable mixture. The cool down
procedure may simply be performed by adding each of the remaining
components, such as the inorganic filler and the remaining water,
before the remaining starch-based binder is added. Depending on
which fraction of the water was added to the preblended mixture
initially, it may be preferable in some cases to add very cold
water or even ice when forming the moldable mixture, or it may even
be necessary to separately cool the preblended mixture using any
appropriate cooling means known in the art.
The mixing procedure used to form the final moldable mixture should
have adequate shear to thoroughly blend the components within the
moldable mixture, but not be so severe that the fibers and
aggregates are damaged, or so that unwanted air pockets are
entrained into the mixture. In addition to the components
identified above, any admixture may be added in order to improve
the moldability of the mixture, or in order to impart the desired
mechanical properties to the molded article. For example,
co-solvents, such as water soluble, volatile alcohols may be added
to aid in the removal of the water from the mixtures during the
molding process. The only limitation to the types of admixtures
that may be added is that they should preferably not unduly
interfere with the gelation process of the starch-based binder
during the heated molding process. Otherwise, a molded article in
which the starch-based binder has been inadequately gelated during
the molding process will generally have inferior mechanical
properties and will be harder to demold without damaging the
articles. If the starch-based binder has been properly gelated, the
molded article will be form stable immediately after being
demolded. The inclusion of well-dispersed fibers, particularly
longer-length fibers having an average length greater than about 2
mm, aids in the ability to obtain a demolded article having
sufficient form stability and resistance to internal pressure
caused by the small amounts of water remaining within the cellular
matrix of the newly demolded article. This in turn yields a newly
demolded article that has sufficient toughness and strength so that
it may be handled immediately or shortly after being demolded
without cracking or failing.
Other mechanical properties that can be designed into the molded
article by changing the mix design and/or molding parameters
include thickness, density, modules of elasticity, compressive
strength, tensile strength, flexural strength, flexibility, range
of strain, insulating ability, and specific heat. Because of the
ability to adjust these properties as needed, a wide variety of
articles can be made, including cups, trays, cartons, boxes,
bottles, crates, spacers, and numerous other articles used for,
e.g., packaging, storing, shipping, serving, portioning, and
dispensing almost any imaginable good, including food or
beverages.
The materials of the present invention may include a variety of
environmentally safe components, including a starch-based binder,
water, inorganic aggregates, fibers, pectins, inert organic
aggregates, mold-releasing agents, rheology-modifying agents,
cross-linkers, dispersants, plasticizers, and coatings. In order to
reduce the cost and also to improve the environmental compatibility
of the articles, the moldable mixtures are designed with the
primary considerations of maximizing the concentration of the
inorganic component, optimizing the starch, fiber, and solvent
components by only including as much of these as is necessary to
obtained the desired properties from each, and selectively
modifying the viscosity and yield stress of the moldable mixture to
produce articles quickly, inexpensively, and having the desired
properties for their intended use.
The starch-based binder acts as the binding agent and typically
includes any starch such as potato starch, corn starch, waxy corn
starch, rice starch, wheat starch, their grain predecessors, e.g.,
flour and cracked grains, or their modified counterparts.
Unmodified starches are generally preferred because they will only
gelate when the moldable mixture has been raised to elevated
temperatures during the molding process, thereby providing a means
for controlling timing, rate, and extent of gelation. In addition,
they are usually far less expensive than modified starches. In some
cases, unmodified starches such as potato starch and corn starch,
the very starches preferred in the present invention, are waste
products and are used as cattle feed or irrigation supplements. The
substitution of naturally produced, but generally overabundant and
low-valued unmodified starches, on the one hand, for the
petroleum-based or synthetically produced plastics, polystyrene,
and other polymers used in the manufacture of conventional
materials, on the other, further illustrates the tremendously
positive environmental impact of the fiber-reinforced,
inorganically-filled, starch-bound materials of the present
invention.
A solvent, typically water, or a combination of water and a
co-solvent such as alcohol, is used to disperse the components
within the mixture, control the viscosity and yield stress of the
moldable mixture, and act as an agent for gelating the starch-based
binder. In addition, other admixtures, such as the starch-based
binder, fibers, inorganic filler component, rheology-modifying
agents, plasticizers, and dispersants, help to create a mixture
having the desired rheological, or flow, properties.
The starch-based binder is preferably added in its ungelated,
granular form, although it may be pregelated, at least in part, in
the preparation of either the preblended mixture or the final
moldable mixture. As the starch-based binder is heated, the
granules rupture, thereby allowing the long, single chain, amylose
polymers located within the granules to stretch out and intertwine
and other starch polymers, such as the highly branched amylopectin
polymers. This process is referred to as gelation. Once the solvent
is removed, the resulting interconnected mesh of starch polymers
produces a solid material. However, the relatively high cost of the
starch-based binder, the excess time and energy necessary to remove
the solvent to make a form-stable article of sufficient strength
and toughness, and the time required to the condition the demolded
article using high humidity make it impractical to manufacture
articles solely out of starch.
To decrease the cost and also to impart desirable properties to the
final article, inorganic fillers or aggregates are added to the
mixture in an amount up to 90% by weight of the total solids in the
mixture. While this range applies to most aggregates of relatively
high density (greater than about 1 g/cm.sup.3), in the case of
lower density, or "lightweight", aggregates (having a density less
than about 1 g/cm.sup.3), such as expanded perlite or hollow glass
spheres, the weight proportion may be less and is dependent upon
the density of the particular aggregate in question. As a result,
it is more appropriate to express the concentration of lightweight
aggregates in terms of volume percent, which will preferably be
included in a broad range from about 5% to about 80% by volume.
To obtain mixtures having a high concentration of inorganics, the
inorganic aggregate particles are selected to have a shape and
particle size demodulation that preferably produces a high packing
density. This process is referred to as particle packing. It is
further preferred that the particles have a relatively low specific
surface area. Using fillers with a high packing density and low
specific surface are minimizes the amount of starch-based binder
and solvent needed in the mixture. By minimizing the starch-based
binder and solvent, the material costs and processing time to
produce the article are minimized. Furthermore, the selection of
aggregates having specific mechanical and physical properties can
be use to impart these properties to the final articles. For
example, the aggregate can help control the specific heat, density,
strength, and texture of the final article. One preferred inorganic
aggregate is calcium carbonate.
The addition of fibers improves the fracture energy and toughness
of the article and improves the form stability and flexibility of
the newly demolded article. One preferred fibrous material is
softwood fibers. Longer-length fibers are preferred over
shorter-length fibers for at least two reasons. Further,
longer-length fibers are better able to bridge or span the length
of the voids or pores within the foamed starch-bound matrix thus
being well-anchored in the matrix and able to have a significant
reinforcing effect. Second, longer-length fibers have a smaller
specific surface area and, hence, are less likely to interfere with
the water-induced gelation process of the starch-based binder.
Fibers may economically be included in amounts from about 2% to
about 40%.
Rheology-modifying agents, such as cellulose-based,
polysaccharide-based, protein-based, and synthetic organic
materials can be optionally added to control the viscosity and
yield stress of the moisture. However, in large amounts they can
compete with and tend to impede the gelation process of the
starch-based binder. In fact, the use of rheology-modifying agents
or thickeners known in the art other than gelated starch generally
cannot be used to attain the high viscosity and yield stress
necessary to disperse most longer-length fibers without adding them
in significantly large amounts. However, the drawback of adding
these large amounts of a thickening agent other than gelated starch
is at least two-fold. First, such thickening agents are generally
far more expensive than gelated, unmodified starches. Second, they
will compete with the gelation reaction of the starch-based binder
with water and at some point prevent the gelation reaction from
occurring altogether, thereby preventing the starch-based binder
from being the primary binding agent and undermining the purpose
for which the starch-based binder was included. By gelating at
least a portion of the starch-based binder during preparation of
the preblended mixture, as well as by increasing the concentration
of inorganic filler or decreasing the amount of water in the final
moldable mixture, the need to add a rheology-modifying agent to
obtain a mixture having the desired viscosity and yield stress can
be greatly reduced or eliminated.
In any event, the prior art only teaches the use of thickening
agents in order to improve the colloidal stability of the mixtures
and thereby retain the inorganic fillers and generally
shorter-length fibers in suspension within the mixture to be
modified. Their use in dispersing longer-length fibers, even if
possible, was not known. Therefore, to the extent that one of
ordinary skill in the art were to use a thickening agent as an aid
in dispersing fibers, particularly longer-length fibers, it would
certainly fall within the purview of the present invention.
In general, increasing the viscosity helps to prevent settling or
separation of the solid components within the moldable mixture and
aids in the formation of the foamed structural matrix. As a general
rule, mixtures that have a high viscosity produce relatively dense
articles having small cells or pores in the structural matrix. In
contrast, mixtures with a low viscosity produce lighter articles
with larger cells or pores within the structural matrix. The
formation of the foamed structural matrix is also dependent on
variables such as the solvent content and the pressure and
temperature applied to the mixture. The rheology-modifying agent
may act as a binder to some extent and can help increase the
strength of the article.
Depending on the amount and average length of fibers that are used
in the moldable mixture, it is possible for the newly demolded
article to be somewhat brittle, particularly where fewer fibers or
those of shorter fiber length are employed. Plasticizers,
humectants, porous aggregates impregnated with plasticizers or
humectants, and the aforementioned fibers may be added to the
mixture to increase the flexibility of the articles. Plasticizers
include materials that can be absorbed by the starch-based binder
to soften the structural matrix, which have a sufficiently high
vapor point so that they are not vaporized and removed from the
matrix during the molding process, and which preferably remain
stable after the article is formed. In addition to water, two
preferred plasticizers include glycerin and polyethylene glycol.
Humectants, such as MgCl.sub.2 and CaCl.sub.2, can absorb moisture
and tightly bind it within the starch-bound structural matrix even
after the molding process. This moisture tends to improve the
flexibility and resilience of the finished article. Porous
aggregates and fibers can retain the water or other plasticizing
agents during the forming process and then disperse them into the
matrix of the form-stable article to increase the flexibility of
the article. Of course, flexibility may also be imparted to the
hardened article through the use of optional high humidity
conditioning.
Hydraulically settable binders such as calcium sulfate hemihydrate
(CaSO.sub.4.1/2H.sub.2O), may be used as a water absorption agent
within the mixtures of the present invention because it reacts with
water to form calcium sulfate dihydrate (CaSO.sub.4.2H.sub.2O).
Water absorbing components may be used to more quickly increase the
viscosity and form stability of the molded article, especially
where larger amounts of water are included initially.
Other components, such as medium- or long-chain fatty acids, their
salts, and their acid derivatives may be added to improve the
release of the hardened article from the mold. Molds having a
polished metal surface, or other non-stick surface, are also useful
in improving or facilitating the release of the article.
Cross-linking agents may be added to improve the strength and
stability of the molded articles. Internal coating agents may be
added which migrate to the surface of the starch-bound matrix as
water is being removed therefrom to form a coating at or
concentrated near the surface of the molded article.
Initially, the selected components are blended into a uniform,
moldable mixture. The mixing can be carded out using a high energy
mixer or an auger extruder, depending on the viscosity of the
mixture. It is often preferred to apply a partial vacuum to the
mixture to remove unwanted air voids, which can create defects in
the final product.
In a preferred embodiment, the moldable mixture is positioned
within a heated mold cavity. The heated mold cavity may comprise
many different embodiments, including molds typically used in
conventional injection molding and die-press molding processes. In
one preferred embodiment, for example, the moldable mixture is
placed inside a heated female mold. Thereafter, a heated male mold
is complementarily mated with the heated female mold, thereby
positioning the mixture between the molds. As the mixture is
heated, the starch-based binder gelates, increasing the viscosity
of the mixture. Simultaneously, the mixture increases in volume
within the heated molds cavity as a result of the formation of
vapor bubbles from the evaporating solvent, which are initially
trapped within the viscous mixture.
Various types of heated molding apparatus known in the art can be
used to mass produce the containers and other articles contemplated
by the present invention, including those used in wafer baking.
Furthermore, conventional expanded polystyrene machines can be
modified to produce the inventive articles.
As will be discussed later in greater detail, by selectively
controlling the thermodynamic parameters applied to the mixture
(e.g., pressure, temperature, and time), as well as the viscosity
and solvent content, the mixture can be formed into a form-stable
article having a selectively designed foamed structural matrix.
That is, the size, quantity, and positioning of the pores can be
selectively designed to produce articles having desired properties
for their intended use. Furthermore, the surface texture and
configuration of the pores within the foamed structural matrix can
be controlled by selectively varying the temperature between the
molds and the temperature along the length of the molds. Besides
controlling the properties among different molded articles, the
properties of a single article can be made to vary throughout the
article, including varying thickness, varying skin thickness,
varying cell structure, and varying density. This may be
accomplished, for example, by creating within the molding apparatus
differential relative temperatures, or differential temperature
zones, throughout the molding apparatus. As a result, different
temperature and processing conditions are imparted to varying
locations throughout the same article.
In a preferred embodiment, the articles are formed from the
previously discussed fiber-containing mixtures to impart the
desired flexibility to the hardened articles without the need for
controlling in high humidity. Residual water, usually about 2-6%,
more preferably 3-4% is retained within the starch-bound matrix
even after the molded article has activated adequate form stability
and resistance to internal pressure so that it can be demolded
without significant deformation of the desired structure of the
article. It is believed that some of the water retained by the
fibers may migrate from the fibers to the hardened starch-bound
matrix over time, thereby further softening the structural matrix
of the article. In addition, further flexibility of the molded
articles may be obtained through conventional conditioning in a
high humidity chamber, where the articles are exposed to elevated
humidity and temperature over time. However, this procedure is
generally unnecessary and cost-ineffective.
Once the article has been demolded, a coating may be applied in
order to seal and provide a more finished surface to the article,
as well as providing additional strength. The coating can be
applied through various conventional processes such as spraying,
dipping, sputtering, and painting. In an alternative embodiment,
so-called "internal coating materials" may be added to the mixture
prior to the formation of the article. If an internal coating
material is used that has a similar melting point as the peak
temperature of the mixture during the molding process, the
individual particles of the internal coating agent will tend to
migrate to the surface of the article during the heated molding
process by the outward flow of the vaporizing water. Upon reaching
the surface of the molded article they are exposed to elevated
temperatures which cause the internal coating particles to melt and
coalesce together and then congeal or solidify at or near the
surface of the article upon demolding and cooling of the article.
Such internal coating materials may include any material having a
melting point that is generally above the boiling point of
superheated water within the molded article and at or below the
maximum temperature of the surface of the article while it is being
molded. They may include, for example, selected waxes, stearates,
shellac, polylactic acid, or any other plastic or polymeric
material having the stated melting criteria. In addition,
nonmigrating materials, such as latexes or polyvinyl alcohol, can
be used to create a general water resistance throughout the
cellular matrix.
The resulting articles can be designed to have properties similar
or even superior to articles made from conventional materials, such
as paper, paperboard, polystyrene, metals, plastic, or other
natural organic materials. In light of the minimal cost of
inorganic fillers and the relatively low cost of unmodified
starches and flours, the inventive articles can also be made at a
fraction of the cost of conventional articles. Finally, the
inventive articles are more environmentally friendly than
conventional articles. For example, the manufacturing process
employs no harmful chemicals, emits no harmful emissions into the
air or water, depletes no non-renewable resources as a starting raw
material for the moldable mixtures, and requires only minimal
processing energy. Furthermore, the inventive articles generally
have low mass, are easily recycled, or quickly decompose back into
the environment.
From the foregoing, an object of the present invention is to
provide novel compositions and methods for manufacturing novel
materials that can replace paper, paperboard, metal, plastic,
polystyrene or other organic materials as the material of choice
for producing containers and other articles.
Another object and feature of the present invention is to provide
compositions and methods for manufacturing organically-bound
materials that can be formed into containers and other articles
currently made from paper, paperboard, polystyrene, metal, plastic,
or other organic materials.
Another object and feature of the invention is to provide
compositions and methods to improve the dispersion of fibers within
such organically-bound materials without the use of large
quantities of water. Yet another object and feature is that such
compositions and methods allow for the dispersion of relatively
long-length fibers (i.e., those having an average length greater
than about 1.5-2 mm) within the organically-bound materials used to
make containers or other articles.
Yet another object of the present invention is to provide
compositions and methods for manufacturing organically-bound
materials that include a relatively large percentage of inorganic
aggregate filler, particularly a filler which is compatible with
and commonly found in the earth.
A further object of the present invention is to provide
compositions and methods that yield highly inorganically filled,
organically-bound articles that had properties similar, or even
superior, to paper, paperboard, metal, polystyrene, plastic, or
other organic materials.
Another object and feature of the present invention is to provide
compositions and methods that allow for the manufacture of
containers and other articles without the need for prolonged,
high-humidity conditioning in order to obtain the required
flexibility or toughness.
A further object is to provide compositions and methods which yield
starch-based articles which do not require the application of a
coating to maintain adequate moisture within the cellular matrix or
to make the cellular matrix water resistant.
An additional object of the present invention is to provide
compositions and methods for manufacturing highly inorganically
filled, organically-bound materials into containers and other
articles having a smoother, more uniform surface compared to
existing organically-bound articles.
Still a further object and feature of the present invention is to
provide compositions and methods for manufacturing articles using
existing manufacturing equipment and techniques presently used to
form such articles from paper, paperboard, metals, polystyrene,
plastic, or other organic materials. Another object is that such
compositions and methods do not result in the concomitant
generation of wastes involved with the manufacture of articles from
such materials.
A further object of the present invention is to provide
compositions and methods that require the use of less water that
has to be removed during the manufacturing process (as compared to
the manufacture of paper or other organically-based materials) in
order to shorten the processing time and reduce the initial
equipment capital investment.
Another object of the present invention is to provide compositions
and methods that make possible the manufacture of containers and
other articles at a cost that is comparable or even superior to
existing methods of manufacturing containers or other articles from
paper, paperboard, metal, plastic, polystyrene, or other organic
materials. Specifically, an important object and feature is that
such compositions and methods result in a reduction in the
consumption of energy, valuable natural resources, and initial
start-up capital presently expended in marking articles from
conventional materials, such as paper, metals, polystyrene,
plastic, or other organic materials.
Yet another object is that such compositions and methods yield
articles having a similar cross-section and comparable mechanical
properties of e.g., insulation, strength, toughness, etc. compared
to paper, paperboard, polystyrene, plastic, or other organic
materials.
An additional object and feature of the present invention is to
provide compositions and methods that allow for the mass-production
of highly inorganically filled, organically-bound articles that can
be rapidly formed and ready to use within a matter of minutes from
the beginning of the manufacturing process.
Finally, a further object and feature of the present invention is
to provide compositions and methods that allow for the production
of highly inorganically filled, starch-based materials having
greater flexibility, flexural strength, toughness, moldability,
mass-producibility, product stability, and lower environmental
impact compared to conventionally manufactured starch-based
materials.
These and other objects and features of the present invention will
become more fully apparent from the following description and
appended claims, or may be learned by the practice of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the manner in which the above-recited and other
advantages and objects of the invention are obtained, a more
particular description of the invention briefly described above
will be rendered by reference to a specific embodiment thereof
which is illustrated in the appended drawings. Understanding that
these drawings depict only a typical embodiment of the invention
and are not therefore to be considered to be limiting of its scope,
the invention will be described and explained with additional
specificity and detail through the use of the accompanying drawings
in which:
FIG. 1 is a phase diagram showing the temperature and pressure
conditions that the mixture is subject to in one embodiment of the
invention during formation of the articles;
FIG. 2 is an enlarged cross-sectional view of the skin and interior
section of a hardened article;
FIG. 2A is a microscopic picture of the cross-section of an article
having a relatively thin outer skin and an interior section
containing relatively larger cells or pores;
FIG. 2B is a microscopic picture of the cross-section of an article
having a relatively thin outer skin and an interior section
containing relatively medium cells or pores;
FIG. 2C is a microscopic picture of the cross-section of an article
having a relatively thick outer skin and an interior section
containing relatively large cells or pores, with longer-length
fibers randomly dispersed throughout the entire cellular
matrix;
FIG. 3 is a cross-sectional view of a male mold and a female mold
being mated;
FIG. 4 is a perspective view of the load cells and mixing
apparatus;
FIG. 5 is a cross-sectional view of an auger extruder
apparatus;
FIG. 6 is a cross-sectional view of a two-stage injector;
FIG. 7 is a cross-sectional view of a reciprocating screw
injector;
FIG. 8 is a perspective view of a male mold and a female mold;
FIG. 9 is a cross-sectional view of a female mold being filled with
a moldable mixture by a filling spout;
FIG. 10 is a cross-sectional view of a male mold and female mole
being mated;
FIG. 11 is a cross-sectional view of the inventive article being
baked between mated molds;
FIG. 11A is an enlarged cross-sectional view of the vent holes
between the mated male mold and female mold;
FIG. 12 is a cross-sectional view of the female mold equipped with
a scraper blade to remove excess material;
FIG. 13 is a cross-sectional view of a dual mold;
FIG. 14 is a cross-sectional view of a split mold with suction
nozzle;
FIG. 15 is a perspective view of a baking machine;
FIG. 16 is a perspective view of a mold in the filling position in
the baking machine of FIG. 15;
FIG. 17 is a perspective view of a scraper blade operating with the
baking machine of FIG. 15;
FIG. 18 is a cross-sectional view of a female mold and male mold
used in a conventional expanded polystyrene machine;
FIG. 19 is a cross-sectional view of the molds used in a
conventional expanded polystyrene machine in a mated position;
FIG. 20 shows a graph illustrating the yield stress and viscosity
of a mixture containing 50 g gelated starch and 800 g water;
FIG. 21 shows a graph illustrating the yield stress and viscosity
of a mixture containing 100 g gelated starch and 800 g water;
FIG. 22 shows a graph illustrating the effect of including varying
amounts of pregelatinized starch on yield stress;
FIG. 23 shows a graph illustrating the effect of including varying
mounts of pregelatinized starch on viscosity;
FIG. 24 shows a graph illustrating the effect of shear rate on
viscosity for a predicted mixture containing 50 g starch and 800 g
water;
FIG. 25 shows a graph illustrating the effect of shear rate on
viscosity for a preblended mixture containing 100 g starch and 800
g water;
FIG. 26 shows a graph illustrating the effect of water content in a
moldable mixture on the skin thickness of a final product;
FIG. 27 shows a graph illustrating the effect of water content in a
moldable mixture on the cell diameter of a foamed product.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
I. INTRODUCTION
The present invention is directed to novel compositions and methods
for manufacturing articles having a generally foamed, highly
inorganically filled, fiber-reinforced, organically-bound
structural matrix. The inventive materials include a variety of
environmentally safe components, including a starch-based binder,
water, inorganic aggregates, and fibers, as well as optional
admixtures such as mold-releasing agents, rheology-modifying
agents, cross-linkers, plasticizers, humectants, dispersants,
organic aggregates, and coating materials.
A materials science and microstructural engineering approach is
used to select the type, size, shape, and proportion of each
component that, when blended together, will result in a moldable
mixture and subsequent final product having the desired properties
at an optional cost. The desired properties are dependent on the
required handling and the intended use of the finished article. The
optimal cost is obtained by selecting components that will maximize
production output while minimizing material and production costs.
By using a microstructure engineering approach, the compositions
and methods of the present invention yield a variety of articles,
including plates, cups, cartons, and other types of containers and
articles having mechanical properties substantially similar or even
superior to articles manufactured using conventional materials,
such as paper, polystyrene foam, plastic, metal and glass The
inventive articles can also be made at a fraction of the cost of
their conventional counterparts due to their inclusion of a
relatively large percentage of inexpensive inorganic aggregate
fillers and lower processing energy requirements.
The manufacturing processes and resulting articles are also less
harmful to the environment compared to conventional materials and
processes. First, theoretically all of the waste associated with
the manufacturing process can be directly recycled back into the
production line. Second, once the generally disposable articles
have fulfilled their intended use, the largely starch-bound
inorganically filled matrix of the article is easily decomposed
back into the earth or recycled. Third, the inventive articles are
of generally low mass and volume.
Preferred moldable mixtures from which the articles of the present
invention are molded include a starch-based binder such as potato,
corn, waxy corn, rice, or wheat starch, an inorganic aggregate such
as calcium carbonate, well-dispersed fibers having an average
length of at least 2 mm, and water. The shape and size distribution
of the inorganic aggregate particles are selected to maximize the
packing density of the particles, thereby reducing the specific
surface area of the aggregate particles and minimizing the
starch-based binder and solvent requirements. The addition of
longer-length fibers (and optionally, significant concentrations of
inorganic aggregate filler) permits the articles to be more quickly
molded and demolded, less expensive, more environmentally safe, and
more resistant to heat compared to articles made with only minimal
amounts of inorganic filler and no longer-length fibers.
Accordingly, the materials and articles of the present invention
are often referred to as being "inorganically filled" or "highly
inorganically filled."
The preferred method for preparing the moldable mixtures of the
present invention involves a two-step process. First, a preblended
mixture is prepared including a portion of the starch-based binder
and water and substantially all of the fibers to be dispersed. The
fibers are thoroughly and evenly dispersed throughout the
preblended mixture by greatly raising the viscosity and yield
stress of the preblended mixture. This allows for a much more
efficient transfer of the shear forces produced by the mixing
apparatus compared to typical fiber slurries employing relatively
large amounts of water in order to obtain better fiber dispersion.
The viscosity of the preblended mixture is increased by gelating
the starch-based binder, which can be accomplished by raising the
temperature of the preheated mixture to the gelation temperature of
the starch-based binder, usually around 65.degree. C. for
unmodified potato starch. Alternatively, the viscosity can be
increased by using a pre-gelated starch, a modified starch that
will gelate when mixed with water at room temperature, or
thickening agents known in the art. Of course, thickening agents
are preferably used to assist rather than take the place of
gelatinized starch is preparing the high viscosity preblended
mixture. In the event that heat is used to gelate the starch-based
binder, it will usually be preferable to cool the preblended
mixture to below the gelation temperature before adding the
remainder of the starch-based binder. Finally, the moldable mixture
is prepared by simply mixing into the preblended mixture the
remaining starch-based binder, water, and other admixtures.
The fibers so dispersed within the moldable mixture increases the
form stability and resistance to internal pressure of the cellular
matrix of the molded articles, which allows them to be more easily
demolded without having to remove substantially all the water from
the starch-bound matrix. That is due in part to the lattice effect
of the fibers, which reinforces the semi-hardened, starch-bound
matrix and allows it to be demolded and handled without significant
deformation or further expansion of the desired shape of the
demolded article. In addition, the fibers are able to more tightly
hold, and thereby retain, water within the structural matrix
compared to the starch-bound binder. As a result, moisture that is
retained within the fibers can migrate into and soften the
otherwise brittle structural matrix of the starch-based binder
after the article has been demolded.
These effects imparted by the fibers allow the demolded articles to
be less brittle and have increased flexibility and resilience
immediately or shortly after being demolded. This obviates, or
greatly reduces, the need for subsequent conditioning of the
starch-bound matrix using high humidity. In addition, the fibers
increase the fracture energy and toughness of the final
articles.
Other admixtures can be combined with the mixture to impart desired
properties to the articles. For example, rheology-modifying agents
and dispersants can be added to additionally regulate the viscosity
of the mixture beyond that already imparted by the starch-based
binder and solid components. Generally, higher viscosity mixtures
yield articles having greater density and smaller pores, while
lower viscosity mixtures yield articles having lower density and
larger pores. Plasticizers and humectants can be used for important
additional flexibility to the molded articles. Other additives
include dispersants, which decrease the viscosity of the mixture
without additional solvent, and selected coating materials, which
can form a coating on the articles during the formation process or
which can be applied after formation of the articles. Aggregate
particles upon which ettringite has been formed may be used to
improve the interaction between the aggregate particles and
starch-based binder.
Once the moldable mixture has been prepared, it is positioned
within a heated mold cavity. The heated mold cavity may comprise
many different embodiments, including molds typically used in
conventional injection molding processes and die-press molding. In
a preferred embodiment, the moldable mixture is placed inside a
heated female mold. A heated male mold is then complementarily
mated with the heated female mold, thereby positioning the mixture
between the molds. By carefully controlling the temperature and
pressure applied to the mixture, as well as the viscosity and
solvent content, the mixture can be rapidly formed into form-stable
articles having a selectively designed foamed structural matrix.
Furthermore, the strength and flexibility of the molded articles
can be controlled by regulating the fiber length and content within
the structural matrix. In general, the surface texture, strength
properties, flexibility, and the formation of the pores within the
structural matrix can be selectively controlled by varying the
components and their relative concentrations within the mixture as
well as the thermodynamic processing conditions. This allows for
the manufacture of a wide variety of containers and other articles
having greatly varying thermal and mechanical properties
corresponding to the performance criteria of the article.
In the preferred embodiment, the articles are formed having the
desired flexibility for their intended use immediately or shortly
after being demolded. Nevertheless, if desired, conventional
conditioning procedures using high-humidity can be used to further
increase the flexibility of the final articles. Water is absorbed
by the hydrophilic starch-based, binder thereby softening and
rendering the structural matrix less brittle.
Finally, coatings can be applied to the surface of the articles of
the present invention in order to protect them from moisture or
otherwise render them impermeable to an attacking agent. Coatings
can be applied to the demolded article using conventional coating
means known in the art, or they may be formed in situ by the use of
internal coating materials capable of migrating to the surface of
the article during the molding process and then solidifying at or
near the surface of the article. Subsequent processing of the
articles may also include printing, stacking, and boxing.
II. DEFINITIONS
The terms "inorganically filled mixture," "mixture," "final
mixture," or "moldable mixture," as used in the specification and
the appended claims, have interchangeable meanings and shall refer
to a mixture that can be formed into the articles which are
disclosed and claimed herein. Such mixtures are characterized by
having a starch-based binder, an inorganic filler or aggregate (up
to about 80% by weight of the total solids in the mixture),
well-dispersed fibers, and a solvent such as water. The mixture may
also include other admixtures, such as mold-releasing agents,
organic aggregates, dispersants, cross-linkers, rheology-modifying
agents, plasticizers, humectants, or internal coating materials.
The mixture can have a wide range of viscosities, from as low as 2
Pas to as high as 10,000 Pas measured at a shear rate of 1
s.sup.-1.
As used in the specification and the appended claims, the terms
"solids" or "total solids" includes all admixtures that are in a
solid or semi-solid state when before being blended with the water
solvent, whether they are suspended or dissolved in the mixture.
Hence, the "total solids" includes the starch-based binder or any
other admixture dissolved within the water solvent. The volume of
the total solids does not include the interstitial voids between
the solids in the final hardened article, but is calculated by
subtracting out the volume of the interstitial voids.
The term "preblended mixture," as used in the specification and the
appended claims, shall refer to any high-viscosity mixture
generally containing gelatinized starch, water, and dispersed
fibers. The viscosity of the preblended mixture is generally at
least about 10 Pas at a shear rate of 1 s.sup.-1, more preferably
above about 50 Pas at a shear rate of 1 s.sup.-1. The viscosity of
the preblended mixture must be sufficient to be able to disperse
the fibers throughout the preblended mixture.
The terms "inorganically filled cellular matrix", "cellular
matrix", "foamed structural matrix" or "starch-bound," as used in
the specification and the appended claims, are interchangeable and
shall refer to the substantially hardened structure of the article
formed by heating the moldable mixture as described herein. The
terms also refer to any starch-bound material in which there has
been an increase in the gross volume of the final molded article
compared to the initial volume of the moldable mixture, such
increase can be as low as 2%, but can be as high as 10 times (100%)
or more.
Both the moldable mixture and the starch-bound matrix formed
therefrom constitute "inorganically filled cellular materials,"
"inorganically filled foamed materials," or "starch-bound
materials." These terms as used in the specification and the
appended claims are interchangeable and shall refer to starch-bound
or starch-containing materials or compositions without regard to
the mount of the solvent or moisture that has been removed from the
moldable mixture and without regard to the extent of gelation of
the starch-based binder.
Because the inclusion of the inorganic filler is optional, though
preferred, the use of the adjectives "inorganic" or
"inorganically-filled" may not apply to all materials made
according to the present invention.
The term "hardening," as used in this specification and the
appended claims, refers to the process of gelation of the
starch-based binder and simultaneous removal of solvent from the
moldable mixture to produce a form-stable article. The term
"hardening," however, is not limited by the extent of gelation or
the amount of solvent removed.
The term "form-stable," as used in the specification and the
appended claims, means that the article has a structural matrix
strong enough to be removed from the mold, support its own weight
against the force on gravity, of the newly demolded starch-bound
matrix, and resist significant deformation when exposed to
subsequent processing and handling. Furthermore, the term
"form-stable" means that the article has sufficient solvent removed
from its matrix so that the article will not bubble or crack as a
result of vapor expansion once the article is removed from the
molds.
III. CONCEPTUAL OVERVIEW OF FORMATION PROCESS
A. Microstructural Engineering Design
The starch-bound materials of the present invention are developed
from the perspective of microstructural engineering in order to
build into the microstructure of the material certain desired,
predetermined properties, while at the same time remaining
cognizant of costs and other manufacturing complications.
Furthermore, this microstructural engineering analysis approach, in
contrast to the traditional trial-and-error, mix-and-text approach,
has resulted in the ability to design starch-bound materials with
those properties of strength, weight, flexibility, insulation,
cost, and environmental neutrality that are necessary for the
production of functional and useful containers and other
articles.
The number of different raw materials available to engineer a
specific product is enormous, with estimates ranging from between
fifty thousand and eighty thousand. They can be drawn from such
disparately broad classes as metals, polymers, elastomers,
ceramics, glasses, composites, and cements. Within a given class,
there is some commonality in properties, processing, and
use-patterns. Ceramics, for instance, have a high modulus of
elasticity, while polymers have a low modulus; metals can be shaped
by casting and forging, while composites require lay-up or special
molding techniques; hydraulically settable materials, including
those made from hydraulic cements, historically have low flexural
strength, while elastomers have high flexural strength and
elongation before rupture.
Compartmentalization of material properties, however, has its
dangers; it can lead to specialization (the metallurgist who knows
nothing of ceramics) and to conservative thinking ("we use steel
because that is what we have always used"). It is this
specialization and conservative thinking that has limited the
consideration of using starch-bound materials for a variety of
products, such as in the manufacture of containers and other
packaging materials.
Nevertheless, once it is realized that starch-bound materials have
such a wide utility and can be designed and microstructurally
engineered to have desired properties, then their applicability to
a variety of possible products becomes appreciable. Such materials
have an additional advantage over other conventional materials, in
that they gain their properties under relatively gentle,
nondamaging, inexpensive conditions. (Other materials require high
energy, severe heat, or harsh chemical processing that
significantly affect the material components and cost of
manufacturing.) Moreover, certain conventional materials, or
components thereof, can be incorporated into the materials of the
present invention with surprising synergistic properties or
results.
The design of the compositions of the present invention has been
developed and narrowed, first by primary constraints dictated by
the design, and then by seeking the subset of materials which
maximizes the performance of the components. At all times during
the process, however, it is important to realize the necessity of
designing products which can be manufactured in a cost-competitive
process.
Primary constraints in materials selection are determined by the
properties necessary for the article to function successfully in
its intended use. With respect to a food and beverage container,
for example, those primary constraints include minimal weight,
strength (both compressive and tensile), flexibility, and toughness
requirements, while simultaneously keeping the cost comparable to
its paper, plastic, polystyrene or metal counterparts.
In its simplest form, the process of using materials science to
microstructurally engineer and design an inorganically filled
article requires an understanding of the interrelationships between
each of the mixture components, the processes parameters (e.g.
time, temperature, pressure, humidity), the mixture properties, and
the properties of the final articles. By understanding the
interrelationships between the variables at both the macro and
micro level, one skilled in the art can select proportions of
desired components that can be processed under selected conditions
to produce articles that have desired properties for an intended
use at a minimum cost.
The interrelationships between the variables will be discussed at
selected locations hereafter where the variables are introduced and
defined. Specific compositions are set forth in the examples given
below in order to demonstrate how the selection of variables can
optimize properties.
B. Articles of Manufacture
The terms "article," "molded article," and "starch-bound article,"
and "article of manufacture," as used in the specification and the
appended claims, are intended to include any article that can be
formed using the disclosed compositions and processes. Examples of
such articles of manufacture include containers, such as food and
beverage containers and packaging containers. Articles within the
scope of this invention also include such disparate objects as
cutlery, flower pots, mailing tubes, light fixtures, ash trays, and
game boards.
The terms "container" or "containers," as used in the specification
and the appended claims, are intended to include any receptacle or
vessel utilized for, e.g., packaging, storing, shipping, serving,
portioning, or dispensive various types of products or objects
(including both solids and liquids), whether such use is intended
to be for a short-term or a long-term duration of time.
Containers within the scope of this invention include, but are not
limited to, the following: cartons, boxes, sandwich containers,
hinged or two-part "clam-shell" containers, dry cereal boxes,
frozen food boxes, milk cartons, fruit juice containers, carriers
for beverage containers, ice cream cartons, cups (including, but
not limited to, disposable drinking cups and cone cups), french fry
scoops, fast-food carry out boxes, packaging, support trays (for
supporting products such as cookies and candy bars), cans, yogurt
containers, sleeves, cigar boxes, confectionery boxes, boxes for
cosmetics, plates, vending plates, pie plates, trays, baking trays,
bowls, breakfast plates, microwaveable dinner trays, "TV" dinner
trays, egg cartons, meat packaging platters, disposable single use
liners which can be utilized with containers such as cups or food
containers, cushioning materials (i.e., "peanuts"), bottles, jars,
cases, crates, dishes, and an endless variety of other objects.
The container should be capable of holding its contents, whether
stationary or in movement or handling while maintaining its
structural integrity and that of the materials contained therein or
thereon. This doe not mean that the container is required to
withstand strong or even minimal external forces. In fact, it may
be desirable in some cases for a particular container to be
extremely fragile or perishable. The container should, however, be
capable of performing the function for which it was intended over
the intended duration of time. The necessary properties may always
be designed into the material and structure of the containers
beforehand using a microstructural engineering approach.
Containment products used in conjunction with the containers are
also intended to be included within the term "containers." Such
products include, for example, lids, straws, interior packaging,
such as partitions, liners, anchor pads, corner braces, corner
protectors, clearance pads, hinged sheets, trays, funnels,
cushioning materials, and other objects used in packaging, storing,
shipping, portioning, serving, or dispensing an object within a
container.
The containers within the purview of the present invention may or
may not be classified as being "disposable" (i.e., manufactured for
a single-service or one-time use). In some cases, where a stronger,
more durable construction is required, the container might be
capable of repeated use. On the other hand, the container might be
manufactured to be economical for a single use and then be
discarded. If produced en mass and then discarded, the articles of
the present invention have a composition that is easily degraded
into environmentally neutral components compatible with earth into
which they may be placed. The starch-bound matrix is quickly
destroyed when exposed to moisture and the components easily
recycled or composted.
The articles within the scope of the present invention can have
greatly varying thicknesses depending on the particular application
for which the article is intended. They can be as thin as about 1
mm for use in e.g., a cup; however, they may be as thick as needed
where strength, durability, and or bulk are important
considerations. For example, the article may be up to about 10 cm
thick or more to act as a specialized packing container or cooler.
Nevertheless, most articles will preferably have a thickness in a
range from about 0.5 mm to about 5 mm, more preferably from about 1
mm to about 3 mm.
The phrases "mass-producible" or manufactured in a "commercial" or
"economically feasible" manner, as used in the specification and
the appended claims, shall refer to the capability of rapidly
producing articles at a rate that makes their manufacture
economically comparable or even superior compared to articles made
from conventional materials, such as paper, paperboard,
polystyrene, plastic or metal.
The containers and other articles made from inorganically filled
materials are intended to be competitive in the marketplace with
such articles currently made of various materials, such as paper,
plastic, polystyrene, or metals. Hence, the articles of the present
invention must be economical to manufacture (i.e., the cost will
usually not exceed a few cents per item). Such cost restraints thus
require automated production of thousands of the articles in a very
short period of time. Hence, requiring the articles of the present
invention to be economically mass-produced is a significant
limitation on the qualities of the materials and products.
C. Processing Concepts and Variables
The present section discusses the underlying concepts and
processing variables used in manufacturing the articles of the
present invention. A detailed description of the mechanical
apparatus and systems used in the manufacturing process will be
provided in a subsequent section.
The mixture of the present invention is prepared by combining
selected components and blending them in a two-step process until a
homogeneous, moldable mixture having well-dispersed components is
formed. The first step involves the preparation of a preblended
mixture having high viscosity in order to more thoroughly disperse
the fibers, particularly longer-length fibers, within the
preblended mixture. The ability to thus include the fibers that
were difficult, if not impossible, to adequately disperse in the
past is a key inventive feature that greatly improves the final
strength and other performance properties of the molded articles.
The inclusion of fibers, particularly long fibers having an average
length greater than about 2 mm, greatly increases the strength and
flexibility of the formed articles, and aids in creating a form
stable and internal pressure resistant product without removing all
of the water from the article as it is being molded. This results
from the reinforcing effect of the long-length fibers forming a
fiber matrix, lattice structure, or skeleton that strengthens the
newly formed starch-bound structural matrix of the articles. In
order to take full advantage of the properties added by the fibers,
it is greatly preferred that the fibers be uniformly dispersed
throughout the moldable mixture and have an average length that is
approximately 2-10 times greater than the cross section of the wall
of the article.
Before it was discovered that increasing the viscosity of the
mixture rather than the water content would result in better
transfer of shear to disperse the fibers, it was particularly
difficult to get a uniform dispersion of long fibers throughout a
starch-based mixture. Only a reduced amount of fiber loading was
possible, and only shorter fibers having an average length less
than about 1.5 mm could be adequately dispersed, which resulted in
inferior molded articles. If one attempted to disperse longer
fibers within a typically nonviscous aqueous slurry, the shear
forces imparted by the mixer to the water did not transfer down to
the fiber level because of the low viscosity of the liquid. Simply
increasing the shear rate of the mixing apparatus was ineffective
and usually led to the degradation of fiber quality before adequate
dispersion was achieved.
For example, in the paper industry, wood pulp fibers are dispersed
in an aqueous slurry having a suspension of 4% by weight of fiber
and 96% by weight of water. Even if dispersion is achieved, a large
amount of energy is then required in order to remove the water from
such slurries, which often contain water in mounts up to about
99.5% by volume. Because so much water must be removed from paper
slurries, it is necessary to literally suck water out of the slurry
even before the drying process is begun.
Such an approach as used in the paper industry would not work in
trying to disperse fibers in a starch-based mixture since there
remains the expensive procedure of removing the large excess of
water. The process of removing the water would result in large
fiber modules rather than the desired dispersion of the fibers. In
contrast to the way fibers are dispersed in the paper industry
using a very high water content, the method of the present
invention uses a lower water content and increased viscosity and
yield stress caused by gelating the portion of the starch-based
binder used in the preblended mixture.
In preparing the preblended mixture, a fibrous material having
individual fibers with an average length greater than about 2 mm
and up to 25 mm is mixed with a portion of the water to form an
initial mixture. A portion of the starch-based binder is then added
to the initial mixture to form a preblended mixture. The
starch-based binder in the preblended mixture is gelated by heating
the mixture to the gelation temperature to greatly increase the
viscosity and yield stress of the preblended mixture, which aids in
the dispersion of the fibers. The preblended mixture is then mixed
at high shear for an effective amount of time to disperse the
fibers therein. The increased viscosity has been found to aid in
transfer of the shearing energy from the mixer to the fibers. In
fact, low viscosity, high water mixtures are unable to impart the
requisite shear energy necessary to completely disperse the fibers,
which energy is mostly dissipated into the water.
The preblended mixture is then cooled to below the gelation
temperature of the starch. The remaining starch-based binder,
water, and other admixtures (including, optionally, an inorganic
filler) are then added to and thoroughly mixed within the
preblended mixture to form a moldable mixture. The moldable mixture
can then be used to produce an article having a desired shape and a
foamed structural matrix, with the article usually being
form-stable within about 30 seconds to about 2 minutes after the
molding process has begun.
A more detailed description of the above methods for preparing the
preblended mixture is as follows. A fibrous material having long
fibers is mixed with a portion of the total water to be added to
form an initial mixture. The fibrous material includes the fibers
having an average length greater than about 2 mm and up to about 25
mm in length. Preferred fibers include softwood fibers from dry
pulp sheets that have an average fiber length of about 3.5 mm and
abaca fibers having an average length of about 6.5 mm. The fibers
are added in an amount in a range from about 2% to about 40% by
weight of the total solids of the final mixture, and preferably in
a range from about 5% to about 30% by weight, and more preferably
in a range from about 10% to about 20% by weight of the total
solids. The portion of water that is added to the initial mixture
is in a range from about 10% to about 90% by weight of the total
water to be added, with about 25% to about 75% by weight being more
preferred, and from about 40% to about 60% being most preferred.
The amount of total water that will be added is selected based on
the desired density of the final product and will preferably be
included in a broad range from about 15% to about 80% by weight of
the final moldable mixture depending on the desired viscosity and
yield stress of the final mixture. Generally, the density of the
final product is inversely proportional to the water content so
that less water results in a higher density final product, while
more water results in more foaming and a lower density final
product.
An initial portion of the starch-based binder is then added to the
initial mixture and then gelated, thereby forming the preblended
mixture. The fraction of the starch-based binder that is added to
form the preblended mixture is determined by the desired level of
viscosity, which should be large enough to adequately transfer
sufficient shearing forces to disperse the particular fiber being
used. Generally, the longer the average fiber length, the greater
the viscosity that is required to adequately disperse the fibers.
Preferably, the fraction of the starch-based binder added to form
the preblended mixture will comprise from about 5% to about 70% by
weight of the total starch-based binder to be added to the final
moldable mixture, with form about 10% to about 50% by weight being
more preferred and from about 10% to about 30% being most
preferred. The amount of starch-based binder added to the preheated
mixture is often roughly equal to about one half the weight of the
fibrous material being dispersed. For example, if 200 g of fibers
were used, then a typical preblended mixture might include about
100 g of starch-based binder. This, however, is more illustrative
and is by no means critical, or even required in many cases.
The starch-based binder in the preblended mixture is then gelated
by heating the mixture to above the gelation temperature of the
starch-based binder, which is usually greater than about 65.degree.
C. for unmodified starches, such as potato starch. The preblended
mixture may be heated by using microwaves when forming the
preblended mixture on a small scale, or by adding preheated water
to the initial mixture. In an industrial setting, it may be more
preferable to mix the fibrous material with the initial portion of
the starch-based binder. This dry mixture is placed into a large
high shear mixer and then preheated water is pumped into the large
mixer, thereby gelating the starch-based binder as mixing
proceeds.
In alternative embodiments, the starch-based binder added to form
the preblended mixture can be pregelated, or a mixture of
pregelated and ungelated starch can be used. The resulting
preblended mixture increases in viscosity and yield stress as the
starch-based binder gelates and thickens the mixture. The viscosity
of the preblended mixture can be controlled by varying the
respective amounts of starch-based binder and water that are used
but will preferably be greater than about 10 Pas at a shear rate of
1 s.sup.-1, and more preferably greater than about 50 Pas, and most
preferably greater than about 100 Pas at the same shear rate. The
preblended mixture is then mixed at high shear for at least about
10 minutes and up to about 2 hours, and preferably from about 10 to
30 minutes, in order to thoroughly disperse the fibers. The length
of the mixing time depends on the viscosity of the preblended
mixture as well as the amount of fibers, with more fibers generally
requiring a longer mixing time.
The preblended mixture is then cooled down to below the gelation
temperature of the starch-based binder, preferably below about
40.degree. C. This may advantageously be performed in some cases by
simply adding the remaining water and other components to the
mixture prior to adding the remaining starch-binder. In other
cases, it may be necessary to add cooler water to further lower the
temperature of the mixture to prevent gelation of the remaining
starch-based binder to be added. The other components such as the
inorganic filers, mold releasing agents, humectants, plasticizers,
and internal coatings or sealing compounds are added at this time
to form the final mixture. The mixture is then mixed for a few
minutes until homogeneous in order to form the desired moldable
mixture, which is then suitable for molding an article having a
foamed structural matrix. It should be noted that the less water
there is in the final mixture, the greater will be the viscosity of
the final mixture and the resulting mixing time required to
disperse the remaining solid components. Preferably, the viscosity
of the moldable mixture can fall within a broad range from about 2
Pas to about 10,000 Pas, and more preferably in a range from about
100 Pas to about 2000 Pas, at a shear rate of 1 s.sup.-1.
In mixing together the components of the moldable mixture it is
important that the remaining part of the starch-based binder not be
subjected to shearing forces large enough to break or rupture the
starch granules, in the case where an unmodified starch is used. It
is also important to maintain the mixture at a temperature below
the gelation temperature of the starch-based binder to avoid
premature gelation of the binder before the molding process has
begun. Otherwise the viscosity of the moldable mixture will become
too high for use in further processing. The moldable mixture needs
to remain sufficiently fluid to be pumped to and flow into a mold
to form a desired article. Pregelatinizing a substantial portion of
the starch-based binder prior to molding would yield a very rigid
gel that would prevent the moldable mixture from flowing into a
mold. By only allowing the initial portion of the starch-based
binder to gelate (e.g., about 10-30% of the starch-based binder),
the moldable mixture maintains a suitable fluidity to flow into the
mold. Once heated within the mold, however, the ungelated
starch-based binder will quickly gelate in order to greatly
increase the viscosity and yield stress of the moldable mixture,
thereby helping to create a form stable molded article that can be
more easily demolded.
The key to getting the fibers to disperse in the preblended mixture
is to obtain a transfer of the shearing force from the mixer to the
liquid in contact with the fibrous material. The shearing force is
an internal force tangential to the material on which the force
acts. When fibers are mixed with low viscosity, high water
mixtures, the fibers are not dispersed since the requisite shearing
force from the mixer is dissipated into the water and does not
transfer to the fibers. Since the water has a lower viscosity, the
water has a tendency to segregate from the fibers and not provide
any shear thereto. Thus, improving the transfer of shear from the
mixer to the liquid in contact with the fibrous material is
necessary in order to disperse the fibers.
The mechanism for obtaining this transfer of shear is through the
higher viscosity of the preblended mixture, which transfers shear
properties from the mixer down to the fibrous material, which
generally results in the dispersion of the fibers within about 10
to 30 minutes with removal of all fiber nodules. This increase in
viscosity by the thickening of the preblended mixture allows a much
greater transfer of the shearing force from the mixer to the liquid
in contact with the fibrous material. This results in the
application of the shearing force to the connections between the
fibers in the fibrous material, which causes the fiber nodules to
be torn apart. The level of transfer of shear by means of the
highly viscous preblended mixtures of the present invention results
in a markedly improved dispersion of fibers compared to
conventional methods. In addition to gelating a portion of the
starch-based binder, various rheology-modifying or thickening
agents can be used to increase the viscosity of the preblended
mixture, such as the commercial thickener Tylose.RTM.. It has been
found, however, that Tylose.RTM. has a very high affinity toward
water, which interferes with the starch-water reaction. Hence,
adding relatively large quantities of rheology-modifying agents
such as Tylose.RTM. is generally not preferred.
The addition of long fibers to the moldable mixture, which are
dispersed throughout the mixture by the method of the present
invention, allows a product to be molded without the need for a
subsequent conditioning step. Unlike prior processes, the products
of the invention can be demolded before all of the water has been
removed from the mixture. The final demolded product maintains an
appropriate amount of water so that the product is not brittle and
can be handled without shattering or cracking.
In addition to fibers, zeolites can be added to the compositions of
the invention and act as internal conditioning components. Zeolites
are aluminum silicates and have a tendency to absorb moisture from
the atmosphere into the structural matrix. Magnesium chloride can
also be used in the compositions of the invention in order to
absorb moisture from the atmosphere and act as an internal
conditioning agent.
Once the mixture has been prepared, it may be formed or molded into
the shape of the desired article. In one embodiment, the forming
steps include positioning and locking the mixture between a heated
male mold having a desired shape and a heated female mold having a
complementary shape. The heat from the molds causes the mixture to
expand within the molds. Excess material and vapor is expelled from
between the molds through small vent holes. Once a sufficient
amount of the solvent has been removed, the molds are opened, and
the form-stable article having a foamed structural matrix is
removed for subsequent processing.
The process is more accurately defined through the use of a phase
diagram. Depicted in FIG. 1 is a phase diagram for water. FIG. 1
illustrates, by way of a general example, the pressure and
temperature stages that a mixture using water as a solvent
undergoes during formation of the article. Between points A and B
along line 1, the mixture is locked between the molds and is
rapidly heated at first at constant ambient pressure to a
temperature of about 100.degree. C. The portion of the mixture
closest to the molds is heated at a faster rate and thus reaches a
temperature of 100.degree. C. before the interior section of the
mixture. As the mixture begins to heat, the starch-based binder
begins to gelate, increasing the viscosity of the mixture. (The
process of gelation is discussed later in the section on
starch-based binders.)
Once the temperature of the water within the moldable mixture in
contact with the mold surface reaches 100.degree. C., the water
begins to vaporize, thereby forming air pockets or voids within the
mixture. As a result of these expanding pockets, the volume of the
mixture expands, causing the mixture to "rise" and momentarily fill
the mold and clog the small vent holes. The water within the
portion of the moldable mixture closest to the molds is quickly
vaporized and driven off from the mixture at or near the region
closest to the mold, as represented in FIG. 1 by point B, thereby
hardening that portion of the mixture into a thin, dense skin. The
skin is believed to be formed almost instantaneously and acts as an
insulation barrier for the remaining portion of the moldable
volume, thereby slowing down the rate of heating. With the vent
holes plugged, and due to the restricted flow, the pressure begins
to increase between the molds, as shown by line 2, preventing the
transformation of the remaining solvent into vapor at the boiling
point, which is usually 100.degree. C. for water. Instead, as also
shown by line 2, the solvent in the moldable mixture is super
heated as a result of the restricted flow. Eventually, the material
blocking the vent holes ruptures, allowing excess material to
escape from between the molds. However, as a result of the small
size of the vent holes, the flow of the escaping mixture is
restricted, thereby allowing the pressure and temperature within
the mold to further increase to point C on FIG. 1.
The foamed structural matrix is formed when sufficient excess
material has escaped to cause the pressure to drop between the
molds. Under high pressure the solvent vapor which forms is
nucleated because of superheating. The drop in pressure causes the
superheated solvent to transform rapidly into the gaseous state
through an adiabatic expansion, thereby forming a distribution of
voids or cells throughout the structural matrix of the article. The
tendency of the solvent vapor to become nucleated at individual
points throughout the superheated mixture yields a fairly
well-distributed cell or pore structure. The transformation of the
solvent to vapor is an endothermic reaction that absorbs heat from
the moldable mixture, thereby substantially decreasing the
temperature of the moldable mixture inside the mold. The drop in
temperature and pressure of the moldable mixture is depicted by
line 3 extending from point C to point B. The illustration that the
temperature of the mixture returns to 100.degree. C. is simply by
way of example. In actuality, the temperature of the mixture may
drop below 100.degree. C. The drop in pressure of the solvent is
depicted as line 5 extending from point C to point D.
With the vent holes open and the pressure reduced, the mixture then
begins to heat up again to the boiling point of the solvent,
allowing the remaining solvent to freely evaporate until sufficient
solvent has been removed for the article to become form-stable.
This process is depicted by line 4 extending from point B. This
analysis of the cellular formation is supported by the fact that
producing articles under low pressure results in articles having
minimal voids. For example, gradually evaporating the solvent from
the mixture at a low temperature or heating the mixture rapidly on
top of a single mold results in a product having a lower
concentration of air voids and high density.
Depicted in FIG. 2 is a cross-section 8 of a formed article. The
figure reveals the present articles as having an outside skin 10
with small cells 12 and an interior section 14 containing large
cells 16. Small cells 12 are defined as having an average diameter
of less than about 250 .mu.m. The material between adjacent cells
is referred to as a cell wall 18. Fibers 21 are distributed
throughout outside skin 10 and interior section 14. The
distribution and size of the cells within the structural matrix are
dependent on several variables including the viscosity of the
mixture, temperature of the molds, and composition of the mixture,
e.g. , the types and amounts of solvent, starch-based binder,
inorganic aggregate, fibers, and other admixtures.
Articles can be made having a desired structural matrix by
controlling the related variables. For example, FIG. 2A is a
microscopic picture of the cross-section of an article having a
thin outside skin 10 and large cells 16 located in interior section
14. FIG. 2B is a microscopic picture of the cross-section of an
article a thin outside skin 10 and medium cells 19 located in
interior section 14. Finally, FIG. 2C is a microscopic picture of
the cross-section of an article having a thick outside skin 10,
large cells 16 located in interior section 14, and small cells 12
located near the surface of the article. In general, the insulation
ability and the strength of the structural matrix of the article
increase as the cells become more evenly dispersed throughout the
matrix. Increasing the overall volume of the cellular space also
would tend to improve the insulation ability, although it would be
expected to have an adverse effect on the strength of the matrix.
The insulation ability can also be improved without significantly
sacrificing strength by adding an efficiently particle packed,
lightweight aggregate to the matrix. The strength is increased by
including fibers that are at least about 1.5 times larger than the
cross section of the article, more preferably 5 times longer, and
most preferably at least about 10 times longer.
The size of the cells within the structural matrix is influenced by
the viscosity and/or of hardening of the article. As previously
discussed, outside skin 10 is formed early on in the process and is
important for the structural integrity of the article. Accordingly,
when the pressure drops and the cells are formed within the
mixture, it is much easier for the vapor to expand within interior
section 14 than in outside skin 10. Thus, the cells are much larger
within interior section 14. It is also possible that the cells in
outside skin 10 are formed at the same time the skin is formed.
That is, as the solvent vaporizes within the portion of the mixture
forming outside skin 10, small bubbles begin to form within the
skin. However, the outside portion of the mixture is heated so
quickly that the skin becomes hard before the cells have a chance
to enlarge.
As stated above, it is important to remove enough solvent so that
the article is sufficiently form stable to be removed from the mold
and subsequently handled. In general, the structural matrix of the
molded articles will contain about 5% or less solvent at the point
where the article has adequate strength and form stability to be
demolded. If excess water vapor remains within the cells of the
heated article, it will cause internal pressure within the
structural matrix of the molded article. This water within the
cellular matrix can further expand after the demolding step,
thereby causing an inadequately dried article to "blow up" or
explode upon being demolded. On the other hand, overdrying,
especially overheating, the article can permanently damage and
weaken the starch-bound structural matrix of the molded
article.
Fortunately, it has been found that the addition of well-dispersed,
longer-length fibers (and optionally, inorganic fillers) creates a
moldable mixture having a much smaller window of error or,
conversely, a much larger window of processing time. That is, these
admixtures facilitate and greatly reduce the time needed to remove
of water in order to create a form stable article, while also
preventing burning or otherwise damaging the starch-bound
structural matrix for a significant period of time during the
molding process.
The processing variables associated with the formation of the
inventive articles and the foamed structural matrix include mold
temperature, time for removing the solvent, filling volume, and
vent hole size. The articles of the present invention are
preferably removed from the locked molds after most, but not all,
of the solvent has been removed. While the mixture is locked
between the molds, the outside edges of the articles are supported
by the opposing molds. Vapor formed by the evaporation of the
solvent is thus forced to travel under pressure to the vent holes,
where it is expelled. The outside walls of the article are the
first to form and are brittle as a result of the loss of water.
Separation of the molds prior to removing a sufficient amount of
the solvent permits the vapor to expand between the article walls,
resulting in bubbling, cracking, or deformation of the outside
walls of the articles. Furthermore, attempts to remove the article
from the molds prior to removal of a sufficient amount of moisture
can result in the article sticking to the molds and damage to the
structural matrix.
Since the article cannot be removed until a sufficient amount of
solvent has been removed, it is preferable to have the mold
temperature as high as possible. This minimizes the time for
removal of the solvent and permits the quickest production of
articles. Studies have found, however, that temperatures greater
than about 240.degree. C. can result in dextrification or breaking
down of the starch molecules in the surface of the article.
Dextrification caramelizes the starch, produces a brown color on
the article, and reduces the structural integrity of the article.
Temperatures above about 240.degree. C. can also burn certain
organic fibers, as well as overdrying the molded articles.
In contrast, it is difficult to form an article having a foamed
structural matrix at mold temperatures below about 120.degree. C.
At such low temperatures, there is little pressure build-up and
only slow evaporation of the solvent. Studies have found that
increasing the processing temperature to between about
140.degree.-240.degree. C. decreases the production time and the
density of the article. With temperatures ranging between
140.degree.-180.degree. C., the decrease in production time is
substantial. After about 180.degree. C., however, the decrease in
processing time is less dramatic. Again, this finding is consistent
with the cellular formation model. The higher temperatures result
in only a marginal decrease in the formation time because they only
marginally shorten the incubation period before the drop in
pressure and they only marginally shorten the time for removing the
moisture after the cellular structure is formed. The temperature of
the molds has little, if any, significant effect on the rate of
formation of the cells after the drop in pressure.
As the temperature increases, the size of the cells also increases.
The size of the cells within the structural matrix, and thus the
strength and insulating capability of the articles, can thus be
selected in part by adjusting the temperature of the molds.
Furthermore, by varying the temperature differential between the
male and female molds, the cell size can be selectively varied
between the walls of the article. For example, by making the female
mold hotter than the corresponding male mold, a cup can be formed
having relatively large cells and higher insulating capability at
its outside surface where the cup is held. In contrast, the cup
will be more dense and be more water tight at its inside surface
where liquid will be held.
A temperature of 200.degree. C. is preferred for the rapid
production of thin-walled articles, such as cups. Thicker articles
require a longer time to remove the solvent and are preferably
heated at somewhat lower temperatures to reduce the propensity of
burning the starch-based binder and fiber. Leaving the articles
within the locked molds too long can also result in cracking or
deformation of the articles. It is theorized that removing greater
than about 98% of the solvent within the mixture results in
shrinking of the structural matrix, which in turn can crack the
article. Accordingly, the article is optimally removed from the
mold when approximately 2%-5% of the moisture remains within the
article, more preferably about 2.5%-4%. It should be understood,
however, that these figures are only approximations.
The temperature of the mold can also affect the surface texture of
the molds. Once the outside skin is formed, the solvent remaining
within the interior section of the mixture escapes by passing
through minute openings in the outside skin and then travelling
between the skin and the mold surface to the vent holes. If one
mold is hotter than the other, the laws of thermodynamics would
predict, and it has been empirically found, that the steam will
tend to travel to the cooler mold. As a result, the surface of the
article against the hotter mold will have a smoother and more
uniform surface than the surface against the cooler mold.
The temperature of the molds can also be varied along the length of
the molds. Depicted in FIG. 3 is a male mold 15 mated with a female
mold 17, with a moldable mixture being positioned therebetween. In
general, the male mold includes a top end 6 and a bottom end 7.
Likewise, the female mold includes a top end 9 and a bottom end 11.
Located near top ends 6 and 9 are vent holes 13, through which the
excess material and vapor can escape. Studies have found that for
deep recessed articles such as cups, a smoother surface and more
uniform structural matrix can be obtained if the mixture is
hardened sequentially from the point furthermost from the vent hole
to the point closest to the vent holes. For example, referring to
FIG. 3, it is preferable in some cases for the temperature of the
molds to be the highest at bottom ends 7 and 11, with the
temperature gradually decreasing toward top ends 6 and 9, where the
temperature is the lowest.
Such a temperature zone differential within the molds helps to
direct the vapor and air out the vent holes. As the solvent is
vaporized at the bottom end of the molds, the vapor is absorbed
into the adjacent mixture. The vapor thus gradually travels to the
vent holes. Furthermore, since the mixture closest to the vent
holes is the last to harden, the excess material is more easily
expelled from between the molds. In contrast, if the molds were
hottest near top ends 6 and 9, the vapor near bottom ends 7 and 11
would be forced to travel over the already hardened surface of the
article, thereby possibly damaging the surface texture. Likewise,
the excess material would already be hardened and its removal could
result in disrupting the structural integrity of the article.
The mold temperature and the time for removing the solvent are
interdependent and are further dependent on the thickness of the
article and the amount of solvent present. The mold temperature of
the present invention is preferably in a range from about
150.degree. C. to about 220.degree. C., with about 170.degree. C.
to about 210.degree. C. being more preferred, and from about
190.degree. C. to about 200.degree. C. being most preferred. The
time in which the solvent is preferably removed from the mixture
ranges from about 1 second to about 15 minutes, with about 15
seconds to about 5 minutes being more preferable, and from about 30
seconds to about 2 minutes being most preferable. It should be
noted that in light of the endothermic process of the vaporization
of the solvent and the rather short period of time that the molds
are in contact with the mixture, the mixture within the interior of
the molded article generally does not get as hot as the molds.
Typically, the temperature of the mixture will not exceed about
130.degree. C. during the molding procedure.
The volume of material positioned between the molds for subsequent
heating also affects the resulting density of an article. If
insufficient material is introduced into the mold to form a
completed article (no excess material is discharged) the resulting
material will have a higher density and moisture content. This
results from a lack of pressure build up and subsequent expansion.
When sufficient material is added to produce the desired pressure
(a minimum of excess material) the density of the article
dramatically decreases.
Further increases in the amount of material will decrease the
density of the article up to a point. Past this point, the addition
of more material will have little or no further effect on the
resulting density. For example, in the production of 12 oz. cups,
the addition of 1 gram of extra material resulted in a decrease in
density of about 0.005 g/cm.sup.3. However, adding more than 35
grams of material resulted in no further decrease in the density
and was merely wasted.
The pressure buildup within the molds is dependent both on the
temperature of the molds and the size of the vent holes. The larger
the vent holes are, the less pressure that builds within the
moldable mixture and the more easily the vapor and excess material
can escape, resulting in less expansion and a more dense structural
matrix of the molded article. Accordingly, the larger the vent
holes, the smaller the cells within the structural matrix. However,
if the vent holes are too large, the mixture will not be able to
plug the vent holes, thereby preventing the required pressure
buildup for the formation of the desired cell structure. (Such an
arrangement may be preferred, however, if a more dense article is
desired.) Another drawback to large vent holes is that they can
create large deformities on the surface of the articles at the
point where the excess material is removed. The size of the
deformities can be reduced by decreasing the size and increasing
the number of the vent holes.
The smaller the vent holes are, the greater is the expansion force
that the vapor can apply on the moldable mixture. If the vent holes
are too small, an excessive pressure will build up, resulting in
deformation or even explosion of the article upon release of the
pressure. The size of the cells can further be regulated by
controlling the release of pressure. For example, by slowing down
the rate of pressure drop, the sudden expansion force caused by
vaporization of the solvent is decreased. This results in articles
having smaller cells and thicker cell walls, which together produce
a stronger article.
As previously discussed, by regulating the size of the vent holes,
the size of the cells in the structural matrix can be regulated.
The exact size and number of vent holes depends on the size of the
article being produced. Larger articles require more vent holes.
Examples of vent sizes and numbers to produce articles are shown
later in the application in the Example Section. In the production
of most articles of the present invention the vent sizes will
preferably range from about 0.05 mm.sup.2 to about 15 mm.sup.2,
more preferably from about 0.2 mm.sup.2 to about 5 mm.sup.2, and
most preferably from about 0.5 mm.sup.2 to about 2 mm.sup.2. The
number of vent holes will preferably be in a range from about 1 to
about 10, with about 2 to about 8 being more preferred, and about 4
to about 6 being most preferred. In a preferred method for
manufacturing cups, it has been found that using 4 vent holes, each
having a vent hole of about 1.9 mm.sup.2, is preferred.
In addition, it is generally preferable to use molds having smaller
vent holes for moldable mixture having a higher water content. When
more water is used, a more violent reaction ensues, which must be
controlled. If the vent holes are too large then material may be
blown out of the vent holes during the molding process. When a low
water content mixture is used, the vent hole size is less
important.
As discussed herein, the inclusion of fibers, particularly
long-length fibers, as well as other softening or conditioning
agents such as humectants or plasticizers within the moldable
mixtures of the present invention, yields demolded articles that
immediately or shortly after demolding possess the desired
flexibility and resiliance. This reduces and, in most cases, even
obviates the need for conventional conditioning in high humidity as
is generally required in the case of molding articles without
fibers and/or inorganic aggregate fillers. Nevertheless, if it is
desired to further soften or condition the starch-bound matrix of
the molded articles, it is possible, although not preferable in
most cases, to condition the articles by placing them in a high
humidity chamber at elevated temperatures for a period of time.
Using the above processes in conjunction with the mixture
components outlined below, the cellular articles of the present
invention will preferably have a density in a range from about 0.05
g/cm.sup.3 to about 1 g/cm.sup.3, with about 0.1 g/cm.sup.3 to
about 0.5 g/cm.sup.3 being more preferred, and about 0.15
g/cm.sup.3 to about 0.25 g/cm.sup.3 being most preferred.
The remaining processing steps include optional steps, such as
printing and coating. These steps, along with stacking, bagging,
and boxing, are performed substantially identically to that of
conventional articles made from materials such as paper, plastic,
polystyrene foam, and other organic materials.
IV. COMPOSITIONAL EFFECTS ON FORMATION
To facilitate implementation of the microstructural engineering
approach, each of the components in the moldable mixture is
discussed below. The discussion includes the properties and
preferred proportions of each of the components, along with how
each component is interrelated with processing parameters,
properties of the moldable mixture, and properties of the final
article.
A. Starch-based binders
The moldable mixtures used to manufacture the inorganically filled,
foamed articles of the present invention develop their strength
properties through the gelation and subsequent drying out of a
substantially solvated starch-based binder. Starch is a natural
carbohydrate chain comprising polymerized sugar molecules
(glycose). Plants manufacture and store the starch as food for
itself and for seeds. Starch is formed in granules that comprise
two types of glucose polymers: the single-chain amylose that is
generally soluble in water and other solvents and the branched
amylopectin that are generally insoluble in water.
In general, starch granules are insoluble in cold water; however,
if the outer membrane has been broken by, e.g. , grinding, the
granules can swell in cold water to form a gel. When the intact
granule is treated with warm water, the granules swell and a
portion of the soluble starch (amylose) diffuses through the
granule wall to form a paste. In hot water, the granules swell to
such an extent that they burst, resulting in gelation of the
mixture. The exact temperature at which a starch-based binder
swells and gelates depends on the type of starch-based binder.
Gelation is a result of the linear amylose polymers, which are
initially compressed within the granules, stretching out and
intertwining with each other and with the amylopectin chains. After
the water is removed, the resulting mesh of inter-connected polymer
chains forms a solid material that can have a tensile strength up
to about 40-50 MPa. The amylose polymers can also be used to bind
individual aggregate particles and fibers within the moldable
mixture (thereby forming a highly inorganically filled matrix).
Through careful microstructural engineering, highly inorganically
filled containers and other articles can be designed having desired
properties including flexural strengths up to with 8 MPa or
more.
Although starch is produced in many plants, the most important
sources are seeds of cereal grains (e.g., corn, waxy corn, wheat,
sorghum, rice, and waxy rice), which can also be used in the flour
and cracked state. Other sources include tubers such as potatoes,
roots such as tapioca (i.e., cassava and maniac), sweet potato, and
arrowroot, and the pith of the sago palm.
As used in the specification and the appended claims, the term
"starch" or "starch-based binder" includes unmodified starches
(amylose and amylopectin) and modified starches. By modified, it is
meant that the starch can be derivatized or modified by typical
processes known in the art such as, e.g. esterification,
etherification, oxidation, acid hydrolysis, cross-linking, and
enzyme conversion. Typical modified starches include esters, such
as the acetate and the half-esters of dicarboxylic
acids/anhydrides, particularly the alkenyl-succinic
acids/anhydrides, ethers, such as the hydroxyethyl and
hydroxypropyl starches; oxidized starches, such as those oxidized
with hypochlorite; starches reacted with cross-linking agents, such
as phosphorus oxychloride, epichlorohydrin, hydrophobic cationic
epoxides, and phosphate derivatives prepared by reaction with
sodium or potassium orthophosphate or tripolyphosphate, and
combinations thereof. Modified starches also include seagel,
long-chain alkylstarches, dextrins, amine starches, and dialdehyde
starches.
Pre-gelatinized starch-based binders can also be added to the
moldable mixture. Pregelatinized starch-based binders are starches
that have previously been gelated, dried, and ground back into a
powder. Since pre-gelatinized starch-based binders gelate in cold
water, such starch-based binders can be added to the moldable
mixture to increase the mixture viscosity prior to being heated.
The increased viscosity prevents settling and helps produce thicker
cell walls as will be discussed later in greater detail. In such
cases, the pre-gelated starch-based binder might be considered to
be acting as a rheology-modifying agent.
Unmodified starch-based binders are generally preferred over
modified starch-based binders because unmodified starches are
significantly less expensive and produce comparable articles. These
starches are very inexpensive and are often treated as a useless
waste product that is discarded on a large scale. Hence, the use of
unmodified starches in the present invention provides a tremendous
economic advantage and a useful outlet for such previously
discarded materials. Preferred starch-based binders include
unmodified starches that gelate and produce a high viscosity at a
relatively low temperature. For example, one preferred starch is
potato starch, which quickly gelates and reaches a maximum
viscosity at about 65.degree. C. The viscosity of potato starch
then decreases as the temperature is raised further. Waxy corn
starch acts in a similar fashion and is also preferred. Both potato
starch and waxy corn starch have a high viscosity and yield stress
when gelated. The high viscosity and yield stress of the gelated
starch greatly enhances the ability of the preblended mixture to
disperse the fibers, as previously discussed.
The high viscosity of potato starch and waxy corn starch when
gelated also aids in holding back steam to form a product having a
foamed structural matrix when the moldable mixture is placed in a
mold. An equation describing the velocity (V) of gas bubbles (such
as steam) toward the surface of a viscous material (such as the
moldable mixtures of the present invention) is set forth as
follows: V.uparw.=d.sup.2(k)/.eta. where d is the diameter of the
bubbles, k is a constant, and .eta. is the overall cohesion or
viscosity of the material. This can be considered an inverse Stokes
sedimentation equation. If the material is more cohesive or
viscous, then the velocity of the bubbles toward the surface will
be reduced. Also, if the bubbles are smaller, the bubbles will have
less of a tendency to migrate toward the surface of the material.
Thus, if the viscosity of a material is increased it has a higher
capacity for holding steam inside and increasing the foaming of the
moldable mixture.
Starch is the dominant water affinity component in the composition
of the present invention and includes many hydroxyl groups. In a
totally dry product, the hydroxyl groups of the individual starch
molecules form hydrogen bonds, which creates a rigid and brittle
structure. When water is added, a portion of the water is tightly
bound to the starch matrix through hydrogen bonding, which is a
very strong force. The water associates with the hydroxyl groups on
the starch, which gives elasticity and toughness to the material.
The water thus acts as a plasticizer that is built into the
moldable mixture of the invention.
A pure starch composition will absorb water such that, at
equilibrium, the water is present in an amount of about 10-12% by
weight of the composition. When inorganic aggregates and fibers are
included in the starch composition, the water will be present in an
amount of about 3-6% by weight at equilibrium because of the less
total starch in the composition.
In order to obtain a more dense material, less starch is used
whereas to obtain a less dense material more starch is needed. The
viscosity of the final moldable mixture can be maintained by
varying the amount of starch added and by varying the total amount
of water and/or fiber. Once a product has been formed, there is a
continuous film of starch and fiber throughout the foamed
structural matrix. The final water content in the formed product is
from about 10 to 15% by weight of the starch. The minimum amount of
starch required in the composition of the present invention is
about 20% by weight.
It may be preferred to combine different types of starch-based
binders to regulate the foamed structural matrix. In contrast to
potato starch, the viscosity of a mixture containing corn starch
gradually increases as the temperature increases. Accordingly, corn
starch produces a relatively low viscosity mixture compared to
potato starch at 65.degree. C., but produces a relatively high
viscosity mixture compared to potato starch at 95.degree. C. By
combining both corn starch and potato starch within the same
mixture, the viscosity of the mixture at the interior section of
the article is increased at the point when the cells are formed.
The increased viscosity decreases the cell size and increases the
cell wall thickness, thereby increasing the fracture toughness of
the article.
The concentration of starch-based binder within the moldable
mixtures of the present invention are preferably in a range from
about 10% to about 80% by weight of total solids, more preferably
in a range from about 30% to about 70%, and most preferably from
about 40% to about 60% by weight. Furthermore, combinations of
different starches may be employed to more carefully control the
viscosity of the mixture throughout a range of temperatures, as
well as to affect the structural properties of the final hardened
article.
B. Solvent
A solvent is added to the moldable mixture in order to lubricate
the particles, solvate or at least disperse the starch-based
binder, and act as an agent for gelating the starch-based binder. A
preferred solvent is water, but can include any liquid that can
disperse and gelate the starch-based binder and be subsequently
removed from the moldable mixture.
The amount of heat energy required to remove the solvent must be
great enough to overcome the boiling point of the solvent being
used. Besides boiling at 100.degree. C., water has a relatively
large heat of vaporization compared to most other solvents,
including alcohols. Both the boiling point and the heat of
vaporization of water can be reduced through the addition of
alcohol co-solvents with the water. Alcohols, such as ethanol and
isopropyl alcohol, are preferable because they form lower boiling
point azeotropic mixtures with water and are relatively inexpensive
and readily available. Production costs may be optimized by using a
mixture of water and alcohol as long as the benefits of using
alcohol co-solvents, such as the savings in time and energy, are
not outweighed by the increased cost of the alcohol.
The solvent also serves the function of creating a moldable mixture
having the desired rheological properties, including viscosity and
yield stress. These properties are general ways of approximating
the "workability" or flow properties of the moldable mixture. The
viscosity of the mixtures of the present invention may range from
being relatively low (similar to that of a thin batter) up to being
very high (similar to paste or clay). Where the viscosity is so
high that the material is initially moldable and dough-like in the
green state, it is generally better to refer to the yield stress,
rather than the viscosity, of the mixture. The yield stress is the
amount of force necessary to deform the mixture. As will be
discussed later, the amount of solvent required to impart a certain
viscosity and/or yield stress to the mixture is highly dependent on
the packing density and specific surface area of the aggregate
material. These are also dependent on the addition of admixtures,
such as rheology-modifying agents and dispersants.
At a minimum, a sufficient amount of the solvent should be added to
disperse and uniformly gelate the moldable mixture. The solvent
content should also be sufficient to function with the processing
equipment. As will be discussed below in greater detail, moldable
mixtures with high viscosity and yield stress may require an auger
apparatus to mix and convey the mixture to the mold. In contrast,
low viscosity mixtures can use conventional mixers to combine the
components and pumps to transfer the mixture.
Increasing the solvent content also increases the number and size
of the cells in the structural matrix and lowers the density of the
resulting article. In theory, the more solvent in a mixture, the
more vapor that is produced, and thus, the more cells that are
formed. Furthermore, the more solvent in a mixture, the lower the
viscosity of the mixture, and thus, the larger the size of the
cells. However, the more solvent added to a mixture, the more time
and energy required to remove the solvent, and thus, the slower and
more expensive the process. In addition, if the solvent content
gets too high, the mixture may be unable to produce form-stable,
crack free articles. In contrast, using low water yields a more
dense product having smaller cells.
Very low viscosity mixtures can also result in settling of the
components, most notably the ungelated starch-based binder and
aggregate particles. Settling may occur in the mixing stage,
transfer stage, or forming stage. Settling can yield articles
having varying properties from batch to batch or within the
structural matrix of a single article. Experiments have also found
that very low viscosity mixtures can splash out of the female mold
during mating with the male mold. This is especially true for
shallow articles such as plates.
Based on the above discussion, the percentage of solvent in the
mixture depends, in part, on the processing equipment, the desired
viscosity, and the desired properties. The amount of water that is
added to the mixtures of the present invention will preferably be
in a range from about 15% to about 80% by total weight of the
mixture, the exact amount depending on the desired viscosity of the
moldable mixture.
As stated above, the viscosity of the moldable mixture is dependent
on several variables such as the water content, the presence of
admixtures such as rheology-modifying agents and dispersants,
whether the starch-based binder has been pre-cooked, and the
packing density of the aggregate. Functional articles can be made
from moldable mixtures having a large range of viscosities, from as
low as about 0.05 Pas to as high as about 10.sup.10 Pas. Low
viscosity mixtures can be poured into the molding apparatus while
high viscosity mixtures may be placed into the molds by auger or
piston insertion. Furthermore, high viscosity mixtures having a
consistency similar to that of clay or dough can be cut into small
portions, which can then be mechanically placed between the
molds.
In general, the moldable mixtures of the present invention will
preferably have a viscosity in a range from about 2 Pas to about
10,000 Pas, and more preferably from about 100 Pas to about 2,000
Pas at a shear rate of 1 s.sup.-1. The rheology of the moldable
mixtures may also be described in terms of yield stress, which will
preferably be greater than about 100 Pa, more preferably greater
than about 400 Pa.
C. Aggregates
The terms "aggregate" and "fillers" as used in the specification
and the appended claims include both inorganic and inert organic
particles but do not typically include fibers. The term "inert
organic particles" is further defined to include organic components
that are not intended to primarily chemically or mechanically act
as a binding agent within the moldable mixture. Examples of inert
organic particles include seeds, grains, cork, and plastic spheres.
Although most aggregates within the scope of the present invention
are insoluble in water, some aggregates are slightly soluble in
water, and some aggregates can be formed in situ by precipitation
or polymerization. (However, many seeds contain starch, proteins,
or other polymeric materials in high enough quantities that they
may be released into the moldable mixture and impart a binding
force within the mixture.)
Although inorganic fillers are generally optional, articles with a
high filler or aggregate content will usually have a lower cost,
improved mechanical and structural properties, better health
safety, and smaller environmental impact. Studies have found that
functional articles of the present invention can be made using no
fliers at all or up to about 80% by weight of the final
article.
From a materials cost stand point, it is more economical to replace
the relatively expensive starch-based binder with a less expensive
aggregate. Typically, the density and weight of an article increase
with increased filler. As the density of the mixture increases, the
volume of material used to make the article also increases. For
example, holding all other variables constant, a 40% increase in
the concentration of calcium carbonate results in about a 30%
savings in the consumption of starch-based binder. It is believed
that as the percentage of filler increases, however, the ability of
the cells within the starch-bound matrix to expand is decreased,
thereby increasing the density and requiring more material to make
the same article. Nevertheless, even with the increase in density,
it may be more economical to produce articles having a higher
filler content compared to those having a relatively low filler
content.
Increasing the filler is also beneficial from a processing
standpoint. Starch has a natural affinity for water (the most
common solvent used). Accordingly, more energy is required to
remove water from the starch-based binder than from a filler. By
increasing the filler content, there is less starch-based binder to
absorb the water and less water is needed to gelate the
starch-based binder. Furthermore, more of the water is absorbed by
the filler. Accordingly, processing costs are decreased by using
high concentrations of filler, since less solvent, time, and energy
is required to produce a form-stable article. Furthermore, the
inorganic aggregate can also be used as a means for conducting heat
quicker and more uniformly throughout the entire structural matrix.
As a result, form-stable articles can be made quicker and with a
more uniform cross-section. The ability of the aggregate to conduct
heat is, of course, a function of the type of aggregate and can be
selected by those skilled in the art.
By selecting an appropriate filler, the specific heat of the final
article can also be decreased. For example, articles made with
calcium carbonate were found to have a lower specific heat than
those that contain only starch. As a result, such articles can be
used for heating up food or other items without significantly
heating up the article. For example, the present articles can be
used for heating up or cooking food in an oven or microwave without
destruction of the article. By selecting fillers with low specific
heat, the articles of the present invention can be made having a
specific heat in a range from about 0.3 J/gK to about 2.0 J/gK at a
temperature of 20.degree. C., with about 0.5 J/gK to about 1.5 J/gK
being more preferred, and about 0.7 J/gK to about 1.0 J/gK being
most preferred.
Increasing the filler content is also beneficial in varying the
shape of the structural matrix of the article. As previously
discussed, if insufficient moisture is removed from the mixture
during formation of the article, the remaining solvent can cause
the mixture to stick to the mold and may also cause the article to
crack or bubble. Likewise, the article can also crack if too much
moisture is removed from the mixture. There is, therefore, a margin
of time (dependent on variables such as the heat of the molds and
amount of solvent in the mixture) within which the articles should
be removed from the heated molds to prevent cracking or sticking of
the articles. This margin of time becomes narrower as the
concentration of starch-based binder within a moldable mixture is
increased. As the margin of time for removal of the article from
the mold decreases, it becomes more difficult to manufacture
articles having cross-sections of varying thicknesses.
In contrast, studies have found that as the percentage of
inorganics increases and the percentage of starch-based binder
decreases, the margin of time in which the articles can be removed
form the molds without sticking or cracking increases. As a result,
articles having a high concentration of inorganics can be used to
more effectively manufacture articles having varying cross-section
thickness. Articles have been made in which the thickness of the
article varies by a factor of three.
There are also health benefits to using higher concentrations of
filler. Increasing the amount of aggregate or filler in a mixture
decreases the amount of water that must remain within the
structural matrix to impart the desired level of flexibility.
Minimizing the amount of water in an article is preferred since it
minimizes the chance for bacterial growth. Accordingly, increasing
the filler content decreases the required moisture content in the
final product, as well as the propensity of the article to absorb
even more water from the atmosphere over time.
By selecting the type of filler used, the properties of the filler
can be transferred to the finished article. The aggregate materials
employed in the present invention can be added to increase the
strength (tensile modulus and, especially, compressive strength),
increase the modulus of elasticity and elongation, decrease the
weight, and/or increase the insulation ability of the resultant
inorganically filled article. In addition, plate-like aggregates
having flat surfaces, such as mica, talc, dolomite, and kaolin, can
be used in order to create a smoother surface finish in the
articles of the present invention. Typically, larger aggregates,
such as calcium carbonate, give a matte surface, while smaller
particles give a glassy surface.
Finally, there are also environmental benefits to having a high
filler content. Articles with a high filler content are more easily
decomposed back into their natural components, thereby minimizing
visual blight. Furthermore, minimizing the starch-based binder
reduces the amount of starch that is consumed from starch-bearing
plants or that must be recycled or composted upon discarding a
disposable article.
Particle packing is a preferred process that can be used to
maximize the amount of inorganics within the mixture and thus
optimize the above discussed properties. Studies have found that
the packing density of a mixture is increased where two or more
types of aggregate having a difference in their average particle
size diameter are used. Particle packing is the processes of
selecting different sizes, shapes, and concentration of the
aggregates to minimize the interstitial space between the particles
and maximize the packing density. By minimizing the interstitial
space, less solvent and starch-based binder needs to be added to
the mixture to fill the interstitial space.
To form an article having a more form-stable, crack-free structural
matrix, the starch-based binder must usually be added in an amount
sufficient to bind the aggregate together. The volume of solvent
and starch-based binder that remains within the final molded
article must be sufficient to coat the aggregate particles and fill
the interstitial voids between the particles so that the
starch-based binder can bind the aggregate particles together. If
insufficient quantities of the starch-based binder are added,
minute pores can form between the aggregate particles. These minute
pores are different from the cells which are preferably designed
within the structural matrix. Whereas the cells result from the
expansion of the solvent during the processing step, the pores
result from an insufficient amount of starch-based binder to bind
the aggregate particles together. If the volume of starch-based
binder is further decreased, the volume of the binder becomes so
minute that either the structural matrix will crack during the
formation process or the mixture will never consolidate into a
form-stable article.
The ability of the starch-based binder to hold the aggregate
particles together is a function of its intrinsic bond strength,
covering power, and its ability to bond with the surface of a
particular material. In the manufacture of articles in which a
binder matrix holds together a very large concentration of matter,
the binder preferably envelops each of the matter particles.
The volume of starch-based binder required to fully envelope the
aggregate particles is related to the volume of interstitial space
between the particles. The volume of interstitial space increases
in a mixture as either the packing density of the aggregate
decreases or the percentage of the aggregate in the mixture
increases. Accordingly, by holding the concentration of
starch-based binder and aggregate constant by weight of the solids
within a mixture and decreasing the packing density of the
aggregate, the interstitial space will increase to a point in which
the volume of starch-based binder is insufficient to adequately
fill the interstitial space. Likewise, by adding a higher
concentration of aggregates, although the percentage of
interstitial space remains relatively constant, the total volume of
interstitial space increases. As a result, more starch-based binder
must be added to the mixture to adequately fill the spaces. As more
starch-based binder is added, however, the concentration of
inorganics decreases in the final articles, thereby increasing the
cost and minimizing the above discussed benefits.
In contrast, as the packing density of the aggregate increases, the
interstitial space between the particles decreases. As a result,
less starch-based binder and solvent are needed to fill the
interstitial space. By decreasing the amount of starch-based binder
to only the minimum amount needed to bind the aggregate particles
and impart the desired physical properties, the percentage of
inorganics in the final articles may be increased without
sacrificing the desired strength and rheological properties. As
such, the cost of the articles is decreased and the above discussed
properties are enhanced.
The volume of starch-based binder required is also dependent on the
size and shape of the aggregate. Aggregates having a large specific
surface area compared to aggregates of equal volume having a small
specific surface area require more starch-based binder to coat the
particles. Coating the aggregate with the gelated starch-based
binder is necessary to bind the aggregate together. In addition,
the greater specific surface area utilizes more of the available
water within the mixture in the coating of the particle surfaces,
resulting in less water being available to react with and gelate
the starch.
Accordingly, in order to maximize the inorganics and minimize the
volume of starch-based binder, it is preferable for the aggregates
to have a smaller specific surface area. The highly inorganically
filled articles of the present invention preferably employ
aggregates having a specific surface area in a range from about 0.1
m.sup.2/g to about 400 m.sup.2/g, with about 0.15 m.sup.2/g to
about 50 m.sup.2/g being more preferred, and about 0.2 m.sup.2/g to
about 2.0 m.sup.2/g being most preferred. Particles having a
relatively small specific surface area typically have a large
average diameter and are spherical in shape.
The following illustrates how increasing the packing density
decreases the amount of solvent and starch-based binder needed to
fill the interstitial space. If the particle packing density of the
moldable mixture is 0.65, a solvent will be included in an amount
of roughly 35% by volume in order to substantially fill the
interstitial voids between the particles. On the other hand, a
moldable mixture having a particle-packing density of 0.95 will
only require solvent in an amount of about 5% by volume in order to
substantially fill the interstitial voids. This is a seven-fold
decrease in the amount of solvent which must be added in order to
substantially fill the interstitial voids. Reducing the amount of
solvent that would otherwise be required to fill the interstitial
space permits the articles to be made more quickly and with a lower
energy consumption.
In order to optimize the packing density, differently sized
aggregates with particle sizes ranging from as small as about 0.05
.mu.m to as large as about 2 mm may be used. To maximize the
strength of the cell walls, it is preferred that the particles not
be greater than 1/4 the thickness of the cell walls. Spherical
particles having minimal fractured surfaces are preferred since
they can be packed to a higher density and have the lowest specific
surface area. In order to obtain an optimized level of particle
packing, it is preferable for the average particle size within one
size range to be roughly 10 times the particle size of the next
smallest particle range. (In many cases, the ratio will differ and
is dependent on the relative natural packing densities of the
different aggregates to be combined.) For example, in a
two-component system, it will be preferable for the average
particle size of the coarse component to be at about 10 times the
average particle size of the fine component. Likewise, in a
three-component system, it will be preferable for the average
particle size of the coarse component to be about 10 times the
average particle size of the medium component, which will likewise
preferably be about 10 times the size of the free component.
Nevertheless, as more differently sized particles are added, the
ratio between the particle size magnitudes need not always be this
great and may only be two-fold in some cases.
In a preferred embodiment, the aggregates are selected to obtain a
desired packing density based on the particle packing process as
disclosed in the following article coauthored by one of the
inventors of the present invention: Johansen, V. & Andersen, P.
J., "Particle Packing and Concrete Properties," Materials Science
of Concrete II at 111-147, The American Ceramic Society (1991).
Further information is available in the Doctoral Dissertation of
Andersen, P. J., "Control and Monitoring of Concrete Production--A
Study of Particle Packing and Rheology," The Danish Academy of
Technical Sciences. The preferred process of particle packing is
also discussed in detail in U.S. patent application Ser. No.
08/109,100, entitled "Design Optimized Compositions and Processes
for Microstructurally Engineering Cementitious Mixtures", to Per
Just Andersen and Simon K. Hodson, filed on Aug. 18, 1993. For
purposes of disclosure, the foregoing article, doctoral
dissertation, and patent application are incorporated herein by
specific reference.
There are a variety of types of aggregates that can be used in the
present invention. Inorganic materials commonly used in the paper
industry, as well as more freely ground aggregate materials used in
the concrete industry, may be used in the moldable mixtures of the
present invention. The size of the aggregate or inorganic filler
will usually be many times greater than the inorganic filler
materials typically used in the paper industry.
Examples of useful aggregates include perlite, vermiculite, sand,
gravel, rock, limestone, sandstone, glass beads, aerogel, xerogels,
seagel, mica, clay, synthetic clay, alumina, silica, fly ash, fused
silica, tabular alma, kaolin, microspheres, hollow glass spheres,
porous ceramic spheres, gypsum (calcium sulfate dihydrate), calcium
carbonate, calcium aluminate, lightweight polymers, xonotlite (a
crystalline calcium silicate gel), lightweight expanded clays,
hydrated or unhydrated hydraulic cement particles, pumice,
exfoliated rock, and other geologic materials. Even discarded
inorganically filled materials, such as discarded containers or
other articles of the present invention can be employed as
aggregate fillers and strengtheners. It will also be appreciated
that the containers and other articles of the present invention can
be easily and effectively recycled by simply adding them to fresh
moldable mixtures as an aggregate filler.
A dry-milled calcium carbonate is a preferred organic aggregate,
since it can be obtained at one-third the cost of calcium carbonate
obtained through wet-milling. A preferred calcium carbonate is
R040, which has a particle size range from about 10 to 150 microns,
with an average particle size of about 42 microns, and a low
specific surface area. Both clay and gypsum are particularly
important aggregate materials because of their ready availability,
extreme low cost, workability, ease of formation, and because they
can also provide a degree of binding and strength if added in high
enough amounts (in the case of gypsum hemihydrate). Because gypsum
hemihydrate can react with the water within the moldable mixture,
it can be employed as a means for hardening, or at least increasing
the form stability of, the moldable mixture.
Gypsum is also a useful aggregate material since it does not affect
the starch-water reactions in the compositions of the invention.
Gypsum dehydrates when heated to about 190.degree. C. to form the
hemihydrate. Upon hydrating, it can harden into a rigid structure
depending on its concentration, thereby imparting delayed, but
additional, binding strength to the final product. Other potential
binders such as hydraulic cement or Tylose.RTM. are not preferred
because they disrupt the gelation reaction between starch and
water.
In some cases, it may be desirable to form ettringite on the
surface of the aggregate particles in order to improve the
interaction and bond interface between the aggregate particles and
the starch-based binder.
Because of the nature of the moldable mixtures and articles made
therefrom, it is possible to include lightweight aggregates having
a high amount of interstitial space in order to impart an
insulation effect within the molded articles. Examples of
aggregates which can add a lightweight characteristic and higher
insulation to the molded articles include perlite, vermiculite,
glass beads, hollow glass spheres, synthetic materials (e.g.,
porous ceramic spheres, tabular alumina, etc.), cork, pumice, and
lightweight expanded clays, sand, gravel, rock, limestone,
sandstone, and other geological materials.
Porous aggregates can also be used to remove unwanted air bubbles
from the article during formation. Solvents escape from the
moldable mixture by first traveling to the surface of the molds and
then traveling along the mold surface to the vent holes. At times,
air bubbles get trapped between the male mold and the outside
surface of the article, thereby pocking the surface. A porous
aggregate within the moldable mixture can be used to absorb a
significant portion of this entrapped gas, thereby helping to
reduce the incidence of pocking. Of course, the entrapped gas
bubbles can be removed through the application of a vacuum.
Porous, lightweight aggregates, including zeolites, can be used as
a means for conditioning the article during the forming process.
Porous aggregates can be presoaked in a solvent or held in the
mixture for a sufficient period of time to absorb the solvent. As
the mixture containing the presoaked aggregate is heated to form
the article, the solvent is released more slowly from within the
porous aggregate than from the remainder of the mixture. As a
result, a portion of the solvent will remain within the porous
aggregate in the form-stable article. Once the article is formed
and removed from the heated molds, the solvent within the porous
aggregate can diffuse into the surrounding structural matrix,
thereby conditioning and softening the structural matrix.
Another class of aggregates that may be added to the inorganically
filled mixture includes gels and microgels such as silica gel,
calcium silicate gel, aluminum silicate gel, and the like. These
can be added in solid form as any ordinary aggregate material
might, or they may be precipitated in situ. Because they tend to
absorb water, they can be added to reduce the water content (which
will increase the viscosity and yield stress) of the moldable
mixture.
In addition, the highly hygroscopic nature of silica-based gels and
microgels allows them to be used as moisture regulation agents
within the final hardened article. By absorbing moisture from the
air, the gels and microgels will cause the articles to retain a
predetermined amount of moisture under normal ambient conditions.
(Of course, the rate of moisture absorption from the air will
correlate with the relative humidity of the air). Controlling the
moisture content of the articles allows for more careful control of
the elongation, modulus of elasticity, bendability, foldability,
flexibility, and ductility of the articles.
It is also within the scope of the present invention to include
polymerizable inorganic aggregate materials, such as polymerizable
silicates, within the moldable mixture. These may be added to the
mixture as ordinary silica or silicates, which are then treated to
cause a polymerization reaction in situ in order to create the
polymerized silicate aggregate. Polymerized inorganic aggregates
are often advantageous in certain applications because of their
increased flexibility compared to most other inorganic aggregate
materials.
The thermal conductivity or "k-factor" (defined as W/mK) of the
present articles can be selected by controlling the foamed
structural matrix. Articles can be made having a low k-factor by
having a higher concentration of cells within the structural
matrix. In embodiments in which it is desirable to obtain a
container or other article having an even higher insulation
capability, it may be preferable to incorporate into the highly
inorganically filled matrix a lightweight aggregate which has a low
thermal conductivity. Generally, aggregates having a very low
k-factor also contain large amounts of trapped interstitial space,
air, mixtures of gases, or a partial vacuum which also tends to
greatly reduce the strength of such aggregates. Therefore, concerns
for insulation and strength tend to compete and should be carefully
balanced when designing a particular mixture.
Preferred insulating, lightweight aggregates include expanded or
exfoliated vermiculite, perlite, calcined diatomaceous earth, and
hollow glass spheres--all of which tend to contain large amounts of
incorporated interstitial space. However, this list is in no way
intended to be exhaustive, these aggregates being chosen because of
their low cost and ready availability. Nevertheless, any aggregate
with a low k-factor, which is able to impart sufficient insulation
properties to the container or other article, is within the scope
of the present invention. In light of the foregoing, the amount of
aggregate which can be added to the moldable mixture depends on a
variety of factors, including the quantity and types of other added
components, as well as the particle packing density of the
aggregates themselves. By controlling the cellular structure and
the addition of lightweight aggregate, articles can be made having
a preferred k-factor in a range of about 0.03 W/mK to about 0.2
W/mK. Insulating articles can have a more preferred k-factor in a
range of about 0.04 W/mK to about 0.06 W/mK. Non-insulating
articles can have a more preferred k-factor in a range of about 0.1
W/mK to about 0.2 W/mK.
The inorganic aggregates may be included in an amount in a range
from about 0% to about 80% by weight of the total solids within the
inorganically filled moldable mixture, with the preferred amount
depending on the desired proper times of the final molded article
and/or the desired rheology of the moldable mixture. If included,
inert organic aggregates will preferably be included in an amount
in a range from about 5% to about 60% by weight of the total
solids. If included lightweight aggregates, defined as those having
a density lower than about 1 g/cm.sup.3, are preferably included in
an amount in a range from about 5% to about 85% by volume of the
inorganically filled moldable mixture.
D. Fibers
As used in the specification and the appended claims, the terms
"fibers" and "fibrous materials" include both inorganic fibers and
organic fibers. Fibers have successfully been incorporated into
brittle materials, such as ceramics, to increase the cohesion,
elongation ability, deflection ability, toughness, fracture energy,
and flexural, tensile, and, on occasion, compressive strengths of
the material. In general, fibrous materials reduce the likelihood
that the highly inorganically filled containers or other articles
will shatter when cross-sectional forces are applied.
As was previously discussed, the formed articles of the present
invention have a foamed or cellular structural matrix. As a result,
there is a limited amount of interfacial surface area for load
transfer between the fibers and structural matrix. That is, the
fibers are connected to the structural matrix of the formed
articles only by the walls dividing the cells, with the remainder
of the fibers suspended in the cells. When short fibers are used,
these can be small enough to reside within the cell completely. As
a result of the minimal contact between the short fibers and the
structural matrix of the article, only a limited portion of the
properties of the short fibers are incorporated into the structural
matrix. Therefore, long fibers having a length of greater than
about 2 mm are preferred for use in the present invention. In
general, it is preferable to include fibers that have an average
length that is at least twice the wall thickness of the article,
and preferably up to 10 times greater or more.
Fibers that may be incorporated into the inorganically filled
matrix preferably include naturally occurring organic fibers, such
as cellulosic fibers extracted from hemp, cotton, plant leaves,
sisal, abaca, bagasse, wood (both hardwood or softwood, examples of
which include southern hardwood and southern pine, respectively),
or stems, or inorganic fibers made from glass, graphite, silica,
ceramic, or metal materials.
Recycled paper fibers can be used, but they are somewhat less
desirable because of the fiber disruption that occurs during the
original paper manufacturing process. Any equivalent fiber,
however, which imparts strength and flexibility is also within the
scope of the present invention. The only limiting criteria is that
the fibers impart the desired properties without adversely reacting
with the other constituents of the inorganically filled material
and without contaminating the materials (such as food) stored or
dispensed in articles made from the material containing such
fibers. For purposes of illustration, sisal fibers are available
from International Filler, abaca fibers are available from Isarog
Inc. in the Philippines, while glass fibers, such as Cemfill.RTM.,
are available from Pilkington Corp. in England.
Studies have found that fibers having a relatively higher diameter
or width are more effective in increasing the energy to failure and
the displacement to failure. For example, sisal fibers having an
average diameter of about 100 .mu.m were far more effective in
increasing the above properties than the wood fibers having an
average diameter of 10 .mu.m. The addition of the sisal fibers also
dramatically decreased the stiffness in the dry cups.
Larger diameter fibers result in less surface area than small
diameter fibers of equal volume. As the exposed surface area of the
fiber decreases, less solvent is adsorbed by the fibers, and,
accordingly, the solvent is removed quicker with less energy. The
fibers used in the present invention preferably have an average
diameter in a range from about 10 .mu.m to about 100 .mu.m, with
about 50 .mu.m to about 100 .mu.m being more preferred, and about
75 .mu.m to about 100 .mu.m being most preferred. Furthermore, the
fibers should have an average aspect ratio (length-to-width ratio)
of at least about 10:1.
The fibers are added to the composition of the present invention to
increase the strength and flexibility of the final product. The
fibers aid in forming a tough skin on the outside of the product by
increasing the flexibility of the skin. The fiber content is
uniform throughout the foamed structural matrix of the final
product, but appears higher in the skin because the skin is higher
in density than the foamed interior portion. Also, a certain amount
of fibers could migrate toward the surface as the product is
forming since the interior portion stays fluid longer than the skin
portion.
The aspect ratio (length/diameter) of the fibers is an important
feature, with a higher average aspect ratio being preferred. The
fibers preferably have an average aspect ratio of about 40:1 to
about 2500:1, and preferably about 200:1 to about 500:1. The total
length of the fibers is also important, with longer fiber lengths
preferred in the present invention. Long fibers that are useful
generally preferably have an average length greater than about 1.5
mm, and more preferably greater than about 2 mm and up to about 25
mm in length. The diameter of the fibers can be about 10 microns to
about 50 microns. Long fibers have a much greater tendency of being
in contact with the structural matrix of the formed articles.
While shorter fibers of less than about 1.5 mm can also be used,
these are less preferred in the present invention. Short fibers,
particularly of less than about 0.5 mm in length, do not work as
well because of their high specific surface area, which absorbs a
lot of moisture, and, especially, their inability to provide
increased strength due to inadequate anchoring to the shorter
fibers within the starch-bound cellular matrix. The high specific
surface area of short fibers interferes with the water-starch
interaction during processing of the moldable mixture by taking
water away from the starch. In addition, the pore size in the
foamed structural matrix of the formed articles is about 0.25 mm,
so when short fibers are used, the fibers will only expand across a
few of the pores. Thus, short fibers would not contribute to
strengthening of the product, but can be used as a filler material
if desired and are preferably used in combination with long
fibers.
Particularly preferred fibers include softwood fibers from dry pulp
sheets that have an average fiber length of about 3.5 mm, and abaca
fibers with an average fiber length of about 6.5 mm. The number of
fibers per unit volume will increase for fibers having smaller
diameters when compared to fibers of the same length with larger
diameters. Having an increased number of fibers per unit volume is
preferred to provide increased strength to the formed articles, and
longer fibers provide more toughness than the same volume percent
of shorter fibers.
The fibers used in the composition of the invention have very
specific effects on the moldable mixture and foamed articles formed
therefrom. There is a toughening effect that can be measured by
peak load. Young's modulus, strain, and fracture energy. Numeric
examples of these properties are given for compositions of the
invention hereafter under the Examples section. The fibers also
have a rheological effect on the compositions related to yield
stress and viscosity. The addition of fibers increases the yield
stress and the viscosity since more energy is needed to get the
moldable mixture to flow.
The fibers also allow an increased or decreased time of the mixture
in a mold without damaging effects such as cracking of the
material. Even if all of the water is taken out of the mixture
during molding by overbaking, the fibers will prevent cracking of
the formed structural matrix, since the fibers reinforce the entire
matrix even while sitting in the mold and prevent the product from
shrinking. The moldable mixture can also be understood without
damage to the product. Underbaking leaves some of the water in the
formed article so that a subsequent conditioning step is not
necessary. Furthermore, when the mold is opened after a shorter
baking time, the formed product can withstand the stresses of the
release of steam because of the internal strength provided by the
fibers. Fibers aid in the ability of the final demolded article to
maintain an appropriate amount of water so that the product is not
brittle and can be handled without cracking. The fibers make the
final product much more resilient and allow the product to be
handled straight out of the mold with little or no damage. The
fibers will also absorb a certain amount of moisture that can later
be released into the starch-bound structural matrix of a formed
article.
In addition, the fibers allow a change in water content in order to
change the density of the final product, whereas pure starch
materials do not have this ability. The water works as a foaming
agent, so if more water is added to the moldable mixture, more foam
will be created and the final product will be less dense. If less
water is used, then less foam will be created and the final product
will be more dense. Thus, the density of the final product can be
changed just by varying the amount of water in the moldable
mixture. The fibers increase the working range of the water in the
moldable mixture by increasing the viscosity thereof, which in turn
allows for use of larger amounts of water while maintaining
adequate post-molding strength.
The amount of fibers added to the moldable mixture will vary
depending upon the desired properties of the final product. The
flexural strength, toughness, flexibility, and cost are the
principle criteria for determining the amount of fiber to be added
in any mix design. The concentration of fibers within the final
hardened article will preferably be in the range from about 2% to
about 40% by weight of the total solids content, more preferably
from about 5% to about 30% by weight, and most preferably from
about 10% to about 20% by weight.
Fiber strength is a consideration in determining the amount of the
fiber to be used. The greater the flexural strength of the fiber,
the less the amount of fiber that must be used to obtain a given
flexural strength in the resulting article. Of course, while some
fibers have a high flexural, tear and burst strength, other types
of fibers with a lower flexural strength may be more elastic. A
combination of two or more fibers may be desirable in order to
obtain a resulting product that maximizes multiple characteristics,
such as higher flexural strength, higher elasticity, or better
fiber placement.
It should also be understood that some fibers, such as southern
pine and abaca, have high tear and burst strengths, while others,
such as cotton, have lower strength but greater flexibility. In the
case where better placement, higher flexibility, and higher tear
and burst strength are desired, a combination of fibers having
varying aspect ratios and strength properties can be added to the
mixture.
It is known that certain fibers and inorganic fillers are able to
chemically interact with and bind with certain starch-based
binders, thereby adding another dimension to the materials of the
present invention. For example, it is known that many fibers and
inorganic fillers are anionic in nature and have a negative charge.
Therefore, in order to maximize the interaction between the
starch-based binder and the anionic fibers and inorganic materials,
it may be advantageous to add a positively charged organic binder,
such as a cationic starch.
Better water resistance can be obtained by treating the fibers with
rosin and alum (Al.sub.2(SO.sub.4).sub.3) or NaAl(SO.sub.4).sub.2,
the latter of which precipitates out the rosin onto the fiber
surface, making it highly hydrophobic. The aluminum floc that is
formed by the alum creates an anionic adsorption site on the fiber
surface for a positively charged organic binder, such as a cationic
starch.
Finally, the fibers may be coated with a variety of substances in
order to improve the desires properties of the final product. For
example, the fibers may be coated in order to make them more
resistant to water absorption. In addition, ettringite can be
formed on the surface of the fibers in order to improve the
interaction or interface between the fibers and the starch-based
binder.
E. Mold-Releasing Agents
To assist in removing the form-stable article from the molds, a
mold-releasing agent can be added to the moldable mixture. Medium-
and long-chain fatty acids, their salts, and their acid derivatives
can be used as mold-releasing agents. The preferred medium and long
chain fatty acids typically occur in the production of vegetable
and animal fats and have a carbon chain greater than C.sub.12. The
most preferred fatty acids have a carbon chain length from C.sub.16
to C.sub.18. The fats and salts used herein need not be in a pure
form but merely need to be the predominant component. That is, the
shorter or longer chain length fatty acids, as well as the
corresponding unsaturated fatty acids, can still be present.
Preferred mold-releasing agents for use in the present invention
include stearates, which have hydrophobic properties and are not
soluble in water. Stearates are salts of stearic acid and have the
general formula of CH.sub.3(CH.sub.2).sub.16COO.sup.-X.sup.+, where
X.sup.+ can be an ion of Al, Mg, Na, K, or Ca. Stearates have
specific melting points that vary depending on what salt is used.
Aluminum stearate is one preferred mold release agent that has been
approved by the FDA. Aluminum stearate has a lower melting point of
110.degree. C. and gives a smoother surface finish to a formed
article. On the other hand, zinc stearate is a health hazard and
should be avoided, especially when forming food or beverage
containers. Generally, a lower melting point or increased amount of
stearate will give a smoother surface to a formed article.
Stearates are grease repellant or resistant, allow the baking time
of a product to be reduced, give a better surface content, provide
heat transfer, and produce a continuous phase. When a clean mold is
used to form products, a seasoning process takes place by using the
stearates in the composition to be formed. The formed products
improve in their surface finish appearance with each molding during
the first few runs. It appears that the stearates on the surface of
the product are getting transferred to the mold surface during the
first few rims to provide the seasoning effect to the mold.
Silicones can also be used as mold releasing agents. Lecithin,
which is a mixture of phosphatides and glycerides, can contribute
to lessening of the stickiness of the moldable mixture, providing
mold-releasing properties, and can improve the flexibility of the
formed articles.
Various waxes such as paraffin and bees wax, and Teflon-based
materials can also be used as mold-releasing agents. One of the
added benefits of using wax is that it can also act as an internal
coating material, as discussed later. Other materials, such as CaS,
calcium silicate and Lecithin, have also been found to work as
mold-releasing agents. To further assist in releasing the articles
from the molds, the molds can be polished, chrome plated, or coated
with, e.g., nickel, Teflon, or any other material that limits the
tendency of the articles to stick to the molds.
The above mold-releasing agents are preferably added to the mixture
in a range from about 0.05% to about 15% by weight of the total
solids, more preferably in a range from about 0.1% to about 10% by
weight, and most preferably in a range from about 0.5% to about 1%
by weight. It is preferred to use a smaller amounts of
mold-releasing agents since agents such as stearates are generally
very expensive.
F. Rheology-Modifying Agents
Rheology-modifying agents can be added to increase the viscosity or
cohesive nature of the moldable mixture in the case where large
amounts of water are included relative to the amount of
starch-based binder used to form the preblended mixture. As
previously discussed, increasing the viscosity decreases the size
of the cells and increases the size of the cell walls within the
structural matrix. Increasing the viscosity also prevents the
natural tendency of the aggregates and starch-based binder
particles to settle within a less viscous mixture. As a result,
during the time period between the preparation and heating of the
mixture to the point of gelation, the aggregate and any ungelated
starch granules may begin to settle, thereby producing an article
having non-uniform properties. Depending on the density of the
aggregate, one of ordinary skill in the art can select the type and
amount of rheology-modifying agent to be added to the mixture to
prevent settling. Nevertheless, it is generally preferred to
include an amount of rheology-modifying agent that will not
substantially interfere with the gelation of the starch-bound
binder.
A variety of natural and synthetic organic rheology-modifying
agents may be used which have a wide range of properties, including
viscosity and solubility in water. Suitable rheology-modifying
agents include cellulose-based materials such as
methylhydroxyethylcellulose, hydroxymethylethylcellulose,
carboxymethylcellulose, methylcellulose, ethylcellulose,
hydroxyethylcellulose, hydroxyethylpropylcellulose,
hydroxypropylmethylcellulose, etc. The entire range of possible
permutations is enormous and shall not be listed here, but other
cellulose materials which have the same or similar properties as
these would also work well.
Other natural polysaccharide-based rheology-modifying agents
include, for example, alginic acid, phycocolloids, agar, gum
arabic, guar gum, locust bean gum, gum karaya, and gum tragacanth.
Suitable protein-based rheology-modifying agents include, for
example, Zein.RTM. (a prolamine derived from corn), collagen
(derivatives extracted from animal connective tissue such as
gelatin and glue), and casein (the principle protein in cow's
milk).
Finally, suitable synthetic organic rheology-modifying agents that
are water dispersible include, for example, polyvinyl pyrrolidone,
polyethylene glycol, polyvinyl alcohol, polyvinylmethyl ether,
polyacrylic acids, polyacrylic acid salts, polyvinyl acrylic acids,
polyvinyl acrylic acid salts, polyacrylamides, ethylene oxide
polymers, polylactic acid, and latex (which is a broad category
that includes a variety of polymerizable substances formed in a
water emulsion; an example is styrene-butadiene copolymer).
Synthetic organic polymers, especially the polyvinyl compounds, are
also used as film binders to produce a hydrophobic surface on the
starch-based binder. The hydrophobic surface slows down the rate of
water absorption by the starch-based binder in the mixing process,
thereby permitting quicker formation of form-stable articles.
G. Dispersants
The term "dispersant" shall refer in the specification and the
appended claims to the class of materials which can be added to
reduce the viscosity and yield stress of the moldable mixture. A
more detailed description of the use of dispersants may be found in
the Master's Thesis of Andersen, P. J., "Effects of Organic
Superplasticizing Admixtures and their Components on Zeta Potential
and Related Properties of Cement Materials" (The Pennsylvania State
University Materials Research Laboratory, 1987). For purposes of
disclosure, the foregoing Master's Thesis is incorporated herein by
specific reference.
Dispersants generally work by being adsorbed onto the surface of
the aggregate particles and/or into the near colloid double layer
of the particles. This creates a negative charge on or around the
surfaces of the particles causing them to repel each other. This
repulsion of the particles adds "lubrication" by reducing the
friction or attractive forces that would otherwise cause the
particles to have greater interaction. This increases the packing
density of the material somewhat and allows for the addition of
less solvent while maintaining the workability of the moldable
mixture. Dispersants can be used to create low viscosity, workable
mixtures having a low concentration of solvent. Such mixtures are
suited for the production of high density articles.
H. Other Admixtures
A variety of other components can be added to the moldable mixture
to impart desired properties to the final article. For example,
enzymes such as carbohydrase, amylase, and oxidase produce holes in
the surface of starch granules permitting the starch-based binder
to gelate faster in the case where ungelated starch is used. As a
result, the viscosity of the mixture increases at a faster rate,
thereby producing articles with a stronger and more uniform cell
structure.
Articles can initially be formed having a desired flexibility (as
opposed to obtaining flexibility through the use of a humidity
chamber) by adding components that will tightly bind the water
within the starch molecules. This can be achieved with the addition
of humectants or deliquescent chemicals, such as MgCl.sub.2,
CaCl.sub.2, NaCl, or calcium citrate. Because all of these
chemicals are readily water soluble, they are able to distribute
and retain water within the starch molecules to provide a more
uniform distribution of moisture. In turn, the moisture improves
flexibility.
Flexibility can also be obtained by adding softeners or
plasticizers to the moldable mixture. Such plasticizers include
Polysorbate 60, SMG, mono and diglycerides and distilled
monoglycerides. Other specialized plasticizers having a boiling
point above the maximum temperature reached by the mixture during
the forming process can also be used. These chemicals, which
include polyethylene glycol (below 600 MW), glycerin, and sorbitol,
tend to take the place of water and function as plasticizers with
moisture as low as 5%. They are believed to attach themselves to
the hydroxyl groups of starch molecules and form a hinge-like
structure. Since the plasticizers do not vaporize during the
forming process, they remain within the form-stable article,
thereby softening the starch-bound matrix. Internal coating
materials that generally have a melting point above the boiling
point of superheated water within the molded article, but below the
maximum temperature achieved at or near the surface of the molded
article while in the mold can be used. These include waxes,
polylactic acid, shellac, or other polymers. In addition, internal
sealing materials such as polyvinyl alcohol and latexes can be
added to generally make the cellular matrix more water
resistant.
Finally, cross-linking admixtures such as dialdehydes, methylureas,
and melamine formaldehyde resins can be added to the mixture to
produce a less water soluble starch-based binder. The cross-linking
admixtures bind to the hydroxyl ions of the starch-based binder,
which slow down the water reabsorption rate of the starch-based
binder. As a result, the final articles obtain form stability at a
faster rate, have higher strength, and are able to retain liquids
longer before failure (e.g., a cup can hold water longer before it
starts to leak).
The above-listed admixtures are typically added in a range between
about 0.5% to about 15% by weight of the total solids in the
mixture, or preferably about 1% to about 10%, and more preferably
from about 1% to about 5%.
V. PROCESSING APPARATUS, CONDITIONS, AND RESULTS
The articles of manufacture of the present invention are produced
through a multistep process. The steps include preparing the
mixture, forming the mixture into the desired articles, and
optionally conditioning the resulting articles. Additional steps
can selectively include the printing, coating, the packaging of the
final articles. The apparatus used in the processing steps are
discussed below. The inventive articles can be prepared using
conventional equipment well known to those skilled in the arts of
polystyrene foam, paper, plastic, cement, and edible wafers. The
equipment, however, must be uniquely combined and arranged to form
a functional system that can manufacture the present articles.
Furthermore, slight modification of the equipment may be required
to optimize production of the articles. The arrangement,
modification, and operation of the equipment needed to manufacture
the inventive articles can be performed by those skilled in the art
of using the conventional equipment in light of the present
disclosure.
A. Preparing the Mixture
As depicted in FIG. 4, the moldable mixture is preferably prepared
in a mixing tank 20 fed by bulk storage cells 22. The number of
storage cells 22 is dependent on the number of components to be
incorporated into the mixture. Storage cells 22 typically comprise
dry load cells 24 and liquid load cells 26. Dry load cells 24 house
solid components such as the starch-based binder, fillers, and
fibers. Dry material metering units 28, typically consisting of
some form of auguring system, automatically and accurately measure
and feed the desired amount of dry mixture into mixing tank 20.
Liquid load cells 26 house liquid components such as the solvent
and different liquid rheology-modifying agents. When appropriate,
automatic stirrers can be positioned within the liquid load cells
26 to help prevent separation or settling of a liquid. Metering
pumps 30 automatically and accurately measure and feed the liquids
into mixing tank 20.
Mixing tank 20 is preferably a high energy mixer capable of quickly
blending the components into a homogenous, moldable mixture. Such
high energy mixers include the TMN turbo batter mixers that are
available from Franz Haas Waffelmaschinen of Vienna,
Industriegesellschaft M.B.H. of Vienna Austria. Alternative high
energy mixers are disclosed and claimed in U.S. Pat. No. 4,225,247
entitled "Mixing and Agitating Device", U.S. Pat. No. 4,552,463
entitled "Methods and Apparatus for Producing a Colloidal Mixture";
U.S. Pat. No. 4,889,428 entitled "Rotary Mill"; U.S. Pat. No.
4,944,595 entitled "Apparatus for Producing Cement Building
Materials"; and U.S. Pat. No. 5,061,319 entitled "Process for
Producing Cement Building Material". For purposes of disclosure,
the foregoing patents are incorporated herein by specific
reference.
Alternatively, a variable speed mixer can be used to provide low
energy mixing. Variable speed mixers include the Eirlch Rv-11.
Where fragile fliers or aggregates, such as glass spheres, are
being incorporated into a mixture, it is preferred to use low
energy mixing so as not to crush the aggregate. Low energy mixing
is more important for high viscosity mixtures. As the viscosity
increases, the shear force applied to the mixture increases,
thereby increasing the damage to the fragile aggregates.
As further depicted in FIG. 4, once the mixture is prepared, it is
pumped through an oscillating screen 32 to a storage mixer 34.
Oscillating screen 32 helps to separate out and disperse unmixed
clumps of the solids. Storage mixer 34 functions as a holding tank
to permit continuous feeding of the moldable mixture to the forming
apparatus. The moldable mixture is fed to the forming apparatus via
a conventional pump 36.
In one embodiment, storage mixer 34 is sealed closed and a vacuum
pump 38 is attached thereto. Vacuum pump 38 applies a negative
pressure to the mixture to remove air bubbles entrained in the
mixture. As previously discussed, air bubbles can cause surface
defects within the final products.
Storage mixer 34 continuously stirs or mixes the moldable mixture
at low energy to prevent settling within the moldable mixture.
Where the forming apparatus operates on batch processing, as
opposed to continuous processing, storage tank 34 can be eliminated
and the mixture fed directly from mixing tank 20 to the forming
apparatus. A complete automated system of load cells and mixers
includes the DANMIX moldable batter mixing system that can be
purchased from Franz Haas Waffelmaschinen Industriegesellschaft
M.B.H. of Vienna, Austria.
Where a thicker or more viscous moldable mixture is desired, it may
be necessary to use an auguring system to mix and transfer the
moldable mixture. In one embodiment, the materials incorporated
into the moldable mixture are automatically and continuously
metered, mixed, and desired by a dual chamber auger extruder
apparatus. FIG. 5 depicts a dual chamber auger extruder 40, which
includes a feeder 42 that feeds the moldable mixture into a first
interior chamber 44 of extruder 40. Within first interior chamber
44 is a first auger screw 46 which both mixes and exerts forward
pressure advancing the moldable mixture through first interior
chamber 44 toward an evacuation chamber 48. Typically, a negative
pressure or vacuum is applied to evacuation chamber 48 in order to
remove unwanted air voids within the moldable mixture.
Thereafter, the moldable mixture is fed into a second interior
chamber 50. A second auger screw 52 advances the mixture toward the
article forming apparatus. Auger screws 46 and 52 can have
different flight pitches and orientations to assist in advancement
of the mixture and performing low and high shear energy mixing.
Auger extruder 40 can be used to independently mix the components
for the moldable mixture, or, as shown in FIG. 5, can be fed by a
mixer 54. A preferable twin auger extruder apparatus utilizes a
pair of uniform rotational augers wherein the augers rotate in the
same direction. Counter-rotational twin auger extruders, wherein
the augers rotate in the opposite directions, accomplish the same
purposes. A pugmil may also be utilized for the same purposes.
Equipment meeting these specifications are available from
Buhler-Miag, Inc., located in Minneapolis, Minn.
High viscosity, moldable mixtures are typically fed into the
forming apparatus by either a two-stage injector or a reciprocating
screw injector. As depicted in FIG. 6, a two-stage injector 56 has
separate compartments for mixing or advancing and injecting. The
mixture is conveyed to an extruder screw 58, which feeds the
mixture to a shooting pot 60. Once shooting pot 60 is filled, an
injection piston 62 pushes a defined quantity of the mixture into a
flow channel 64 that feeds the forming apparatus.
As depicted in FIG. 7, a reciprocating screw injector 66 comprises
a chamber 68 having a screw auger 70 longitudinally positioned
therein. The moldable mixture is fed into chamber 68 and advanced
by screw auger 70. As screw auger 70 rotates, it retracts and feeds
the mixture to injection end 72 of screw auger 70. When the
required volume of the mixture has accumulated at end 72, screw
auger 70 stops rotating and moves forward to inject the mixture
into flow channel 64 and subsequently to the forming apparatus.
B. Forming the Mixture into the Desired Article
Once the mixture is prepared, it is preferably formed into the
desired shape of the article through the use of heated molds. FIG.
8 depicts a heated male mold 74 having a desired shape and a heated
female mold 76 having a complementary shape. Female mold 76
comprises a mold body 78 having a flat mold face 80 with a
receiving chamber 82 bored therein. Receiving chamber 82 has a
mouth 84 through which it is accessed. Male mold 74 comprises an
attachment plate 86, a die head 88 having a shape substantially
complementary to the shape of receiving chamber 82, and a venting
ring 90 extending between attachment plate 86 and die head 88.
Venting ring 90 is slightly larger than mouth 84 of receiving
chamber 82 and contains a plurality of venting grooves 92 that are
longitudinally aligned with die head 88.
In the preferred embodiment, the molds are vertically aligned with
female mold 76 being positioned below male mold 74. In this
orientation, as shown in FIG. 9, receiving chamber 82 acts as a
container for receiving the moldable mixture from a filling spout
94. Once the mixture is positioned within female mold 76, the molds
are mated, as shown in FIG. 10, by inserting die head 88 into
receiving chamber 82 until vent ring 90 comes to rest on mold face
80 around mouth 84. Die head 88 is slightly smaller than receiving
chamber 82 so that when the molds are mated, a mold area 96 exists
between male mold 74 and female mold 76. As previously discussed,
the amount of moldable mixture positioned in female mold 76
preferably only fills a portion of mold area 96.
In the mated position as shown in FIGS. 11 and 11A, vent grooves 92
communicate with mold area 96 to form vent holes 98. Furthermore, a
venting gap 100 is formed between mold face 80 and attachment plate
86 as a result of venting ring 90 resting on mold face 80. During
operation, the heated molds cause the moldable mixture to expand
and dry into a solid article according to the process and
parameters as previously discussed. Excess material 102 and vapor
is expelled from mold area 96 through vent holes 98 and into
venting gap 100. Once the mixture becomes form-stable in the
desired shape of the article, male mold 74 and female mold 76 are
separated. As depicted in FIG. 12, a scraper blade 103 can then be
pressed along the length of mold face 80 to remove excess material
102.
The molds can have a variety of shapes and sizes to form the
desired article. However, there are two general types of molds:
dual molds and split molds. As shown in FIG. 13, dual mold 104
comprises a single male mold 74 and a single female mold 76. This
type of mold is used for making shallow articles, such as plates
and lids, that are easily removed from the molds. Split molds 106,
as shown in FIG. 14, comprise a single male mold 74 and a female
mold 76 that can be separated into mold halves 106. Mold halves 108
are separated after the article is formed to permit easy removal of
the article. Split molds 106 are used for the production of deep
recessed articles such as cups and bowls that can be difficult to
remove from a mold.
One method for removing articles from the mold is by a suction
nozzle 110. As shown in FIG. 14, suction nozzle 110 has a head 112
with vacuum ports 114 located thereon. Head 112 is designed to
complementarily fit within the hardened article. Accordingly, by
inserting head 112 into the article and applying a slight negative
pressure through vacuum ports 114, the article can be picked up and
moved to a conveyor belt for subsequent processing.
The molds are preferably made of metals such as steel, brass, and
aluminum. Polished metals, including chrome and nickel, along with
Teflon coatings, make it easier to remove the articles from the
molds and create a smoother finish. The material of the molds must
be able to withstand the temperatures and pressures, as previously
discussed, encountered during the manufacturing process.
The molds can be heated in a variety of ways. For example, external
heating elements, such as gas burners, infrared light and
electrical heating elements, can be attached or directed at the
molds. Alternatively, heated liquids, such as oils or heated gases,
such as steam, can be piped through the molds to heat them. Various
types of heating can also be used to vary the temperature of the
molds along the length of the molds in order to vary the properties
of the hardened matrix within the molded article. It is also
possible to heat the mixtures without heating the molds. For
example, the molds can be made out of ceramic and microwaves be
applied to heat the mixture.
By varying the temperature and processing time it is possible to
affect the density, porosity, and thickness of the surface layer,
or skin. Generally, in order to yield a molded article having a
thinner but more dense surface layer, the molding temperature is
lower, the molds have fewer vents, and the moldable mixture has a
higher viscosity. The viscosity of the mixture can be increased by
adding a rheology-modifying agent, such as Tylose.RTM., including
less water, or by using an aggregate material having a higher
specific surface area.
One method for mass producing the articles of the present invention
is by means of the baking machine depicted in FIG. 15. As depicted
in FIG. 15, baking machine 116 has a forming station 118 attached
to and communicating with a baking oven 120. Baking oven 120
includes an insulation wall 122 that defines an oven chamber 124.
Heating elements 126 are positioned within oven chamber 124 for
heating oven chamber 124. A track system 128 extends through both
forming station 118 and oven chamber 124 in a continuous, circular
fashion. Track system 128 includes an upper track 130 and a lower
track 132. Riding on tracks via wheels 134 are a plurality of
interconnected, hingedly attached baking molds 136. As best shown
in FIG. 16, each mold has a top plate 138 and a bottom plate 140
with the plates being connected together at one end by a hinge 142.
Top plate 138 and bottom plate 140 include a male mold 74 and a
female mold 76, respectively, as previously described.
Baking machine 116 functions as a continuous process to mass
produce desired articles. Production of the articles is performed
in several stages that are simultaneously being performed by
different baking molds 136 in the chain of molds. As shown in FIG.
16, in the first stage, baking molds 136 are open and positioned
under a filling spout 144 for receiving the moldable mixture.
Baking molds 136 are opened by separating the upper and lower
tracks 130 and 132 on which the top and bottom plates 138 and 140
ride, respectively. Filling spout 144 is used to discharge a
selected quantity of the moldable mixture into female mold 76.
Once female mold 76 is filled, baking molds 136 advance and are
closed as a result of upper and lower tracks 130 and 132 closing
together. To facilitate cyclic separation of the molds, as
previously discussed, the tracks can be designed to cyclicly
diverge and converge as shown at point C on FIG. 15, thereby
repeatedly opening and closing the molds. Once cyclic separation is
completed, the molds are locked and the forming process is
continued.
One preferred mechanism for locking the molds is described in U.S.
Pat. No. 4,953,453, issued Sep. 4, 1990, to Franz Haas, Sr. and
entitled "Apparatus for Operating Locks of Baking Tongs for
Producing Rotatable, Preferably Edible Wafers from Wafer Dough in a
Water Baking Oven or an Automatic Wafer Baking Machine"
(hereinafter the "Haas '453 patent"). For purpose of disclosure,
the above patent is incorporated herein by specific reference. The
Haas '453 patent discloses a locking mechanism that prevents the
forcing of the lock or disruption of the process when the molds
fall to properly align and close. More conventional locking
mechanisms can be used; however, they must be able to withstand the
pressures produced by the heated mixtures.
Baking mold 136 travels the length of baking oven 120, rotates to
an inverted position, and then travels back to forming station 118.
In accordance with the present invention, heating elements 126 are
positioned within oven chamber 124 for heating baking molds 136 as
they travel through oven chamber 124. By way of example and not by
limitation, heating element 126 can include electrical heating
elements, gas burners, and infrared lights.
The speed at which the molds travel through baking oven 120 is in
part limited by the required time it takes to stop and fill baking
molds 136. The filling time is, of course, dependent on the size of
the article being molded. The time that the mixture remains in the
oven is dependent on several variables, including the solvent
content, oven temperature, and filing volume, as previously
discussed. To permit the adjustment of the forming time without
modifying the speed of the molds, baking oven 120 is built to
include unit sections 146. Unit sections 146 can be removed from
baking oven 120 or new sections can be added to baking oven 120 so
as to permit selective adjustment of the length of baking oven 120.
The forming time and temperature are selected to that when baking
molds 136 return to forming station 118, the article can be removed
from the molds in a form-stable condition.
Referring again to FIG. 15, once the molds return to forming
station 118, baking molds 136 are again opened by separating upper
and lower tracks 130 and 132. A scraper blade 148, depicted in FIG.
17, can then be passed over female mold 76 to remove excess
material 102 that may have exited through vent holes 98 during the
heating process. The article can then be removed from female mold
76.
The articles can be removed from the molds in a variety of
different manners. For example, as shown in FIG. 16, when dual
molds 184 are used, as the separated molds pass through forming
station 118, the molds are again rotated so as to invert back into
their original orientation. As the molds are rotated, the force of
gravity causes the article to fall out of baking molds 136. A
conveyer belt can then be used to catch and transfer the article
for subsequent processing. When split molds 106 are used, the
removal process entails separating of mold halves 108 and allowing
the articles to fall down a collection chute 149 under the force of
gravity, as shown in FIG. 15. The articles then continue along a
conveyor belt through the remaining processing steps. With the
articles removed form the molds, the molds return to filling spout
144 and the process is repeated.
A typical baking machine 116 may be selected from a variety of
commercially available baking machines, such as the SWAK T. SWAK I,
and SWAK wafer baking machines, and the STAK, STAZ and STA ice
cream cone machines. These baking machines can be purchased from
Franz Haas Waffelmaschinen Industriegesellschaft M.B.H. of Vienna,
Austria. Although the above-listed machines have been used in the
past primarily for the production of edible wafers and ice cream
cones, the listed machines can be used in the present invention by
inserting the proper mold shapes, which have been selectively
modified as previously discussed, depending on the desired
processing parameters and the type of article to be produced.
As an alternative to the Haas baking equipment, conventional
expanded polystyrene manufacturing equipment (hereinafter "EPS
machine") can be modified to produce the articles of the present
invention. As depicted in FIG. 18, a conventional EPS machine
comprises a male mold 150 and a female mold 152, the molds being
vertically aligned with female mold 152 being on top. Female mold
152 includes a mold body 154 having a receiving chamber 156 defined
by a mold wall 158. At one end of mold wall 158 is a mounting lip
160. Located within mold wall 158 is a female wall cavity 162.
Communicating with receiving chamber 156 is a filling channel 164
that is selectively opened and closed by a piston 166. Finally,
communicating with filling channel 164 is a filling tube 168 that
is also opened and closed by piston 166.
Male mold 150 has a die head 170 having a shape substantially
complementary to receiving chamber 156. Die head 170 has a base
172, a side wall 174, and a top 176. Circumferentionally located
within die head 170 near top 176 is a chamber 178. Positioned
within chamber 178 is an expandable vent spring 179. Chamber 178
communicates with a pressure tube 180 positioned within die head
170. Chamber 178 also communicates with the environment through a
venting slot 181 that extends between chamber 178 and the exterior
of male mold 150. Located at base 172 is a venting groove 182 that
is complementarily aligned with mounting lip 160. Finally, a male
wall cavity 184 is positioned within die head 170 near side wall
174 and top 176.
During typical operation of the EPS machine, the molds are
initially mated, as shown in FIG. 19, to form a mold area 186
between the molds. Air is blown through filling channel 164 into
mold area 168 and exits through a vent gap 188 located between
mounting lip 160 and venting groove 182. The blowing air causes a
suction that pulls polystyrene beads located in filling tube 168
into mold area 186. Venting gap 188 is sufficiently small to
prevent the polystyrene beads from escaping.
Once the mold area is filled with the polystyrene beads, filling
channel 164 is closed by piston 166. Steam is passed into female
wall cavity 162 and male wall cavity 184 heating female mold 152
and male mold 150. Steam is also blown into mold area 186 through
pressure tube 180 and venting slot 181. As the steam enters
chambers 178 through pressure tube 180, the pressure resulting from
the steam causes vent spring 179 to expand, permitting the steam to
pass through venting groove 182. Once the steam is stopped, venting
spring 179 retracts, preventing material from in mold area 186 from
entering into chamber 178.
As a result of the heated steam, the polystyrene beads heat,
expand, and melt together forming the desired article. Cold water
is then passed through female wall cavity 162 and male wall cavity
184 to cool the molds and subsequently harden the polystyrene
article. Once the article is formed, the molds are separated and
the article removed. The article is most easily removed by blowing
air through chamber 178 which pushes the article off male mold
150.
A conventional EPS machine can be used in a couple of different
methods to produce the articles of the present invention. In the
first method, the EPS machine is used in substantially its normal
configuration. By using a mixture having a consistency similar to
that of a wet powder, the mixture can be sucked into mold area 186
by passing air through filling channel 164. However, since the
mixture of the present invention hardens upon being heated, as
opposed to cooled, the wall cavities 162 and 184 should be
continually heated by steam or other heated liquids like oil. It is
also preferred to insulate and cool filling tube 168. Heating of
filling tube 168 can result in the gelation and hardening of the
starch-based binder, thereby clogging tube 168. Nevertheless, by
providing a cool-down cycle after the heating cycle, it is possible
to demold the articles while maintaining enough moisture within the
structural matrix to keep it flexible without the need for a
subsequent conditioning step.
By regulating the size of vent gap 188, pressure can be built up
within mold area 186, thereby producing the foamed articles in the
same manner as previously discussed. One advantage of using the EPS
machine in its normal configuration is that the final articles
remain on male mold 150 after the molds are separated. The article
can then be easily removed by blowing air through pressure tube
180.
In an alternative method, the molds of the EPS machine can be
inverted so that female mold 152 is vertically aligned below male
mold 150 and acts as a receptacle for the moldable mixture. The
mixture can then be poured into female mold 152 through an external
spout while the molds are open. The molds can then be closed and
the article formed in the same manner as previously discussed.
A modified expanded polystyrene (EPS) machine can be used in
forming articles from the compositions of the present invention.
The modified EPS machine is an injection molding system having thin
wall with a lower heat capacity so the heat can be removed easier
during hot and cold cycling, which occurs through the use of hot
steam and cold water. In using this system, the mold is opened and
the mixture is injected therein. The mold is then closed and
sealed, and the mixture is heated to about 200.degree. C. The
starch in the mixture gelates, becomes plastic, and flows in the
heated mold. The vent holes are then opened to expand the material
and create a foamed structural matrix. The mold is then cooled
before removal of the product, and the starch gel solidifies and
maintains conditioning water in the structural matrix. The mold is
then opened to remove the finished product which has form
stability.
C. Coatings and Coating Apparatus
It is within the scope of the present invention to apply coatings
or coating materials to the articles. Coatings can be used to alter
the surface characteristics of the articles in a number of ways,
including sealing and protecting the article. Coatings may provide
protection against moisture, base, acid, grease, and organic
solvents. Coatings may also fill in voids on the surface of the
article and provide a smoother, glossier, or scuff-resistant
surface. Furthermore, coatings can help prevent aggregate and fiber
"fly away." Coatings may also provide reflective, electrically
conductive, or insulative properties. They may even reinforce the
article, particularly at a bend, fold, edge or corner. Some of the
coatings can also be utilized as laminating materials or as
adhesives.
Application of a coating may also be used to regulate the moisture
content of the present articles. It is theorized that the moisture
content of an article will eventually reach a point of equilibrium
with its environment. That is, relatively dry articles will adsorb
moisture in a humid climate and conditioned articles will lose
moisture in a dry climate. The application of a coating after
conditioning the article to the proper moisture content can prevent
the exchange of moisture between article and the surrounding
environment.
The object of the coating process is usually to achieve a uniform
film with minimal defects on the surface of the article. Selection
of a particular coating process depends on a number of substrate
(i.e., article) variables, as well as coating formulation
variables. The substrate variables include the strength,
wettability, porosity, density, smoothness, and uniformity of the
article. The coating formulation variables include total solids
content, solvent base, surface tension, and rheology.
The coating can be applied either during the forming process or
after the article is formed. The coating can be formed during the
forming process by adding a coating material that has approximately
the same melting temperature as the peak temperature of the
mixture. As the mixture is heated, the coating material melts and
moves with the vaporized solvent to the surface of the article
where it coats the surface. Such coating materials include selected
waxes and cross-linking agents.
The coatings may be applied to the article after formation by using
any coatings means known in the art of manufacturing paper,
paperboard plastic, polystyrene, sheet metal, or other packaging
materials, including blade, puddle, air-knife, printing, Dahlgren,
gravure, and powder coating. Coatings may also be applied by
spraying the article with any of the coating materials listed below
or by dipping the article into a vat containing an appropriate
coating material. The apparatus used for coating will depend on the
shape of the article. For example, cups will usually be coated
differently than flat plates.
As the articles having a starch-based binder have a high affinity
for water, the preferred coatings are non-aqueous and have a low
polarity. Appropriate coatings include paraffin (synthetic wax);
shellac; xylene-formaldehyde resins condensed with
4,4'-isopropylidenediphenolepichlorohydrin epoxy resins; drying
oils; reconstituted oils from triglycerides or fatty acids from the
drying oils to form esters with various glycols (butylene glycol,
ethylene glycol), sorbitol, and trimethylol ethane or propane;
synthetic drying oils including polybutadiene resin; natural fossil
resins including copal (tropical tree resins, fossil and modern),
damar, elemi, gilsonite (a black, shiny asphaltite, solbule in
turpentine), glycol ester of damar, copal, elemi, and sandarac (a
brittle, faintly aromatic translucent resin derived from the
sandarac pine of Africa), shellac Utah coal resin; rosins and rosin
derivatives including rosin (gum rosin, tall oil rosin, and wood
rosin), rosin esters formed by reaction with specific glycols or
alcohols, rosin esters formed by reaction formaldehydes, and rosin
salts (calcium resinate and zinc resinate); phenolic resins formed
by reaction of phenols with formaldehyde; polyester resins; epoxy
resins, catalysts, and adjuncts; coumarone-indene resin; petroleum
hydrocarbon resin (cyclopentadiene type); terpene resins;
urea-formaldehyde resins and their curing catalyst;
triazine-formaldehyde resins and their curing catalyst; modifiers
(for oils and alkyds, including polyesters); vinyl resinous
substances such as polyvinyl chloride, polyvinyl actete, polyvinyl
alcohol, etc.; cellulosic materials (carboxymethylcellulose,
cellulose acetate, ethylhydroxyethylcellulose, etc.); styrene
polymers; polyethylene and its copolymers; acrylics and their
copolymers; methyl methacrylate; ethyl methacrylate; waxes
(paraffin type I, paraffin type II, polyethylene, sperm oil, bees,
and spermaceti); melamine; polyamides; polylactic acid; Biopol.RTM.
(a polyhydroxybutyrate-hydroxyvalerate copolymer); soybean protein;
other synthetic polymers including biodegradable polymers; and
elastomers and mixtures thereof. Biopol.RTM. is manufactured by ICI
in the United Kingdom. Appropriate inorganic coatings include
sodium silicate, calcium carbonate, aluminum oxide, silicon oxide,
kaolin, clay, ceramic and mixtures thereof. The inorganic coatings
may also be mixed with one or more of the organic coatings set
forth above.
In some cases, it may be preferable for the coating to be
elastomeric or deformable. Some coatings may also be used to
strengthen places where the articles are severely bent. In such
cases, a pliable, possibly elastomeric, coating may be preferred. A
waterproof coating is desirable for articles intended to be in
contact with water. If the articles are intended to come into
contact with foodstuffs, the coating material will preferably
comprise an FDA-approved coating.
Polymeric coatings such as polyethylene are useful in forming
generally thin layers having low density. Low density polyethylene
is especially useful in creating containers which are liquid-tight
and even pressure-tight to a certain extent. Polymeric coatings can
also be utilized as an adhesive when heat sealed.
Aluminum oxide and silicon oxide are useful coatings, particularly
as a barrier to oxygen and moisture. The coatings can be applied to
the article by any means known in the art, including the use of a
high energy electron beam evaporation process, chemical plasma
deposition and sputtering. Another method of forming an aluminum
oxide or silicon oxide coating involves the treating of the article
with an aqueous solution having an appropriate pH level to cause
the formation of aluminum oxide or silicon oxide on the article due
to the composition of the article.
Waxes and wax blends, particularly petroleum and synthetic waxes,
provide a barrier to moisture, oxygen, and some organic liquids,
such as grease or oils. They also allow an article such as a
container to be heat sealed. Petroleum waxes are a particularly
useful group of waxes in food and beverage packaging and include
paraffin waxes and microcrystalline waxes.
The various products made from the composition of the present
invention are porous so a coating needs to be used for water
resistance. If there is moisture contact with an uncoated product,
such as contact from food or beverages, the material of the product
will be softened. While solvent based coatings can be used, it is
preferable to use water based coatings. Preferred coatings that can
be used include acrylic based coatings such as various acrylic
emulsions, and vinyl based coatings including waxes such as
paraffin wax, shellac, polyvinyl alcohol, and polylactic acid. When
water based coatings are used, the water is removed to coalesce the
coating particles on the surface of a formed product.
Both external and internal coating methods can be used on the
articles formed from the compositions of the present invention. In
the external coating method, two different systems can be used. The
first is a sprinkle system in which freely powdered wax is
dispensed or sprinkled onto the surface of a newly formed product
sitting in an open mold, which causes the wax to melt over the
surface of the product. The mold temperature is about 200.degree.
C. and the temperature on the exposed surface of the product in the
open mold is about 100.degree. C. Since the melting point of wax is
about 50.degree. C., the wax is easily melted on the surface of the
product when sprinkled thereon.
The second system for external coating that may be used is a spray
system in which wax is first melted and then sprayed at a
temperature higher than the wax melting point so that molten wax is
dispersed on the surface of a formed article. The spray system can
be used to apply wax to the inside surfaces of a product in a mold
can be used to spray one or both sides of a product that has been
demolded and placed on a conveyer. The spray system can be used to
apply water based or hot melt coatings such that small droplets of
the coating are applied to a product surface and coalescence of the
coating particles takes place.
When water is added with the coating or a water-based coating is
used, an additional conditioning component is added to the formed
product. The structural matrix of the product will absorb the water
from the coating into the matrix to provide additional moisture
thereto. The coating can also be flash dried on the surface and at
the same time leave the moisture on the inside of the product for
conditioning of the matrix.
In one preferred internal coating method of the present invention,
polyvinyl alcohol (PVA), latex, or other plastics are used as
internal coatings. These coating materials are dissolved in water
and built into the moldable mixture so that when a product is
formed, the coating material will be dispersed throughout the
formed structural matrix. When using PVA, which is made from
polyvinyl acetate, a PVA with a higher hydrolysis is easier to
dissolve in water. The dissolving of PVA into solution is also a
function of temperature and time. A 2% solution of PVA has a long
dissolution time of 15 minutes, a high molecular weight and a high
hydrolysis rate.
Another internal coating method that can be utilized is to disperse
waxes, stearates, polylactic acid, shellac, latex, or other
plastics internally in a moldable mixture, followed by migration of
a secondary phase of coating particles to the skin at the surface
of a product during molding where the coating particles coalesce to
form a coating over the surface of the product.
D. Printing
It may be desirable to apply print or other indicia, such as
trademarks, product information, container specifications, or
logos, on the surface of the article. This can be accomplished
using any conventional printing means or processes known in the art
of printing paper or cardboard products, including planographic,
relief, intaglio, porous, and impactless printing. Conventional
printers include offset. Van Dam, laser, direct transfer contact,
and thermographic printers. However, essentially any manual or
mechanical means can be used.
The type of printing and printer used depends in part on the shape
of the article. For example, flat plates will require a different
printing apparatus than a cup. In addition, the molds can be
specially designed to provide embossing on the surface of the
article. The article can also be provided with a watermark. Because
the articles have a relatively high porosity, the applied ink will
tend to dry rapidly. One skilled in the art will appreciate that
the article porosity and ink quantities must be compatible. In
addition, decals, labels or other indicia can be attached, or
adhered to the article using methods known in the art.
E. Physical Properties of the Articles
In view of the foregoing, it is possible, by using a
microstructural engineering approach, to obtain a wide variety of
articles of varying shapes, strengths, flexibilities, stiffness,
insulation, and other physical properties. In general, the flexural
strength of the articles will preferably be in a range of about 0.5
MPa to about 8 MPa, more preferably in a range from about 0.75 MPa
to about 6 MPa, and most preferably in a range from about 1 MPa to
about 4 MPa. The range of strain of the articles (i.e., the amount
of strain before rupture) will preferably be in a range from about
1% to about 15%, more preferably from about 1% to about 10%, and
most preferably from about 1% to about 5%. The specific strength of
the articles will vary in a range from about 2 MPa-cm.sup.3 to
about 80 MPa-cm.sup.3. The fracture energy of the articles will
preferably be in a range from about 5 J/m.sup.2 to about 3000
J/m.sup.2, more preferably from about 15 J/m.sup.2 to about 1500
J/m.sup.2, and most preferably from about 25 J/m.sup.2 to about 600
J/m.sup.2.
The products that are made from the composition of the invention
have a laminate-type structure formed in situ. There is an outer
skin layer on both sides having a higher density and an interior
foam portion with a lower density. The outer skin layer is created
instantaneously when the moldable mixture is contacted with the
mold. The pores formed in the interior foam portion have a diameter
of about 0.25 mm. The interior foam portion is a viscous liquid
during the molding process and includes a starch gel that is
plasticized under high temperature and pressure between the outer
skin layers. The interior foam portion hardens when the moisture is
removed during the molding process. By increasing the water
content, the density of the final product will be lowered, but a
longer baking time is required since more water must be driven
off.
VI. EXAMPLES OF THE PREFERRED EMBODIMENTS
Outlined below are a number of examples showing the manufacture of
articles from the inorganically filled, starch-bound, moldable
mixtures of the present invention. The examples compare the
properties of the articles for varying compositions and processing
conditions. In the first group of examples, articles were formed
with inorganic fillers but without fibers, which articles required
conditioning to obtain adequate flexibility.
Examples 1-13
Drinking cups were formed from moldable mixtures containing
different types of inorganic aggregates to determine the effects of
the different aggregates. Each of the moldable mixtures had the
following basic mix design measured by weight:
TABLE-US-00001 39.8% Stalok 400 (modified potato starch) 9.95%
inorganic aggregate 49.75% water 0.5% magnesium stearate
Each moldable mixture was prepared in a small Hobart mixer. First,
the dry ingredients (including the inorganic aggregate, starch, and
magnesium stearate) were completely mixed. Then the water was added
slowly while the dry materials were being mixed until a homogeneous
mixture was obtained. The mixtures were extracted from the Hobart
mixing bowl using a syringe. The weight of the moldable material
used to manufacture a cup for each mixture was determined by first
weighing the syringe containing the moldable mixture, expelling the
contents of the syringe into the molding apparatus, and then
weighing the syringe.
The molding system included a male mold made out of tooled brass
and a female mold made out of tooled steel, the molds being
configured substantially according to FIG. 8. The molds were
designed to produce 12 oz. drinking cups having a smooth surface
and a thickness of about 4 mm. The male mold contained four vent
grooves that formed four vent holes.
The cups of Examples 1-13 were obtained by heating each selected
moldable mixture between the molds at a temperature of about
200.degree. C. Once the articles became significantly form-stable,
they were removed from the molds and placed in an oven for about
1.5 hours at a temperature of 105.degree. C. to remove the
remaining moisture. The moisture was removed so that subsequent
testing of the cups would better reflect the effects of the
component as opposed to the effects of the starch-based binder
moisture content. It was assumed that the weight loss of the cup
during drying in the oven was a loss of water. The measured weight
loss was thus used to determine the moisture of cups upon being
removed from the mold. The cups were then sealed in plastic bags to
maintain a constant humidity until the cups could be tested.
Summarized below is a list of the selected inorganic aggregates and
the resulting properties of the cups formed from each of the mix
designs:
TABLE-US-00002 Moisture Thermal Cup Out of Thermal Resist.
Inorganic Density Mold Conduct. (ft.sup.2-h-.degree. F./ Example
Aggregate (g/cc) (% W/W) (W/m K) BTU-in) 1 Gamma Sperse 0.190 3.0
0.046 3.15 2 Carbital 50 0.185 2.5 0.044 3.25 3 R040 0.215 2.7
0.045 3.20 4 Mica 4k 0.205 2.6 0.048 3.10 5 Glass Bubbles 0.190 4.9
0.047 3.15 B38/4000 6 Polymica 400 0.195 2.0 0.049 2.90 7 Aerosil
R972 0.125 4.2 0.040 3.68 8 Aerosil 130 0.135 4.0 0.054 2.70 9
Aerosil 200 0.145 4.1 0.046 3.15 10 Aerosil 380 0.155 4.3 0.048
3.10 11 Cabosil EH5 0.140 2.8 0.041 3.60 12 Wollastonite 0.195 2.1
N/A N/A 13 Sil-co-sil 0.200 2.1 N/A N/A Silica Sand Displace-
Energy to ment to Peak Inorganic Failure Failure Load Stiffness
Example Aggregate (mJ) (%) (N) (N/m) 1 Gamma Sperse 6.0 3.1 5.00
2.5 2 Carbital 50 9.0 3.5 5.10 2.7 3 R040 7.0 3.1 5.05 2.6 4 Mica
4k N/A N/A N/A N/A 5 Glass Bubbles 9.5 3.2 5.20 3.4 B38/4000 6
Polymica 400 10.0 2.7 5.15 2.4 7 Aerosil R972 7.0 4.0 4.95 1.9 8
Aerosil 130 7.0 3.5 4.90 1.8 9 Aerosil 200 9.0 3.5 5.00 2.1 10
Aerosil 380 6.0 3.1 4.95 2.2 11 Cabosil EH5 7.0 3.4 4.95 2.0 12
Wollastonite 8.5 3.1 5.10 2.9 13 Sil-co-sil 8.0 2.8 5.05 3.0 Silica
Sand
The properties analyzed include thermal properties and mechanical
properties. The thermal properties include thermal conductance and
thermal resistivity which were determined by a transient hot-wire
method. Three measurements were recorded for the thermal
conductivity of the side walls of the cups and the average value
was reported. Mechanical properties were defined by developing a
test that would simulate the pinching between the thumb and the
other four fingers that a cup might experience during use. The
results served as a means to compare cups produced from different
compositions and under different conditions. The strength and
ductility were not easily quantifiable due to the complex geometry.
Instead the data is reported without normalization to the
cross-sectional area.
The cups were positioned on an inclined platform. The inclination
was adjusted so that the side edge of the cups was normal to the
loading direction. The area below the top rim of the cup was chosen
as the point of load application. This resulted in the most
reproducible results. Loads were applied to the cups at the rate of
15 mm/min. until a clear failure was observed. The displacements
and the corresponding loads were recorded.
The test provided a qualitative evaluation of the mechanical
properties. Using the defined testing method, a comparison was made
on the basis of peak load, maximum displacement before failure,
energy absorbed during fracture, and stiffness. The energy of
failure is the area under the load displacement curve measured from
the origin to the point of first fracture. Each of the above
properties are based on a statistical average of seven identical
tests.
The tests showed that the fumed silica aggregate (Aerosil R972,
130, 200, 380 and Cabosil EH5) resulted in a density of about 30%
lower compared to those where a different inorganic aggregate was
added. The other inorganic aggregates had a limited effect on the
density of the cups, with the exception of Polymica which also
decreased the density by about 30% relative to cups using the other
inorganic aggregates.
The dry peak load and stiffness of the cups containing fumed silica
were affected to the same extent as the density; approximately 30%
of each was lost compared to cups produced without fumed silica.
The dry displacement-to-failure and energy-to-failure measurements
exhibited little or no change due to the addition of inorganic
materials.
The addition of Mica 4 k glass bubbles, Wollastonite, Polymica 400,
and silica sand, did not affect the energy-to-failure
displacement-to-failure, peak load, and stiffness to any
significant degree. The one exception was Mica 4 k which had a 30%
increase in peak load. The value for thermal properties were found
to be in a band width of about .+-.10% of the value for cups
produced with no starch-based binder substitute. The values were
independent of the type of inorganic aggregate used.
Based on the above tests, fumed silica aggregates appear to be less
preferred since they adversely affect the mechanical properties of
the articles. In contrast, the other inorganic aggregates can be
used to replace at least 20% by weight of the starch-based binder
without significantly affecting the mechanical properties of the
articles. It is believed that fumed silicas produce a detrimental
effect as a result of their low strength in comparison to the other
inorganic aggregates.
Example 14-18
Cups were made using collamyl starch with different concentrations
of calcium carbonate to determine the effect of using collamyl
starch. The same procedures and apparatus set forth in Examples
1-13 were used to make and test the cups of Examples 14-18. A base
mixture was first prepared by combining the following components by
weight:
TABLE-US-00003 49.75% collamyl starch and RO40 calcium carbonate
49.75% water 0.5% magnesium stearate.
The calcium carbonate was added to the mixture in amounts of 20,
40, 50, and 60% by total weight of the calcium carbonate and
starch-based binder. Summarized below are the properties of the
articles made using different percentages of calcium carbonate.
TABLE-US-00004 Calcium Dis- Carbonate Thermal place- Ex- Aggregate
Den- Conduct. Energy ment to Peak Stiff- am- (weight sity (W/m to
Fail. Failure load ness ple %) (g/cc) K.) (mJ) (%) (N) (N/m) 14 0
0.17 0.043 6 3.5 4.5 1.9 15 20 0.17 0.043 7 4.3 4.5 1.7 16 40 0.24
0.046 7 3.5 5.2 2.2 17 50 0.27 0.045 7 3.2 5.8 2.5 18 60 0.32 0.053
7 2.6 6.5 3.5
The increase in density was negligible for the first 20% of RO40
calcium carbonate that was added. For higher concentrations, the
increase was substantial, being about 2% for each weight percent of
added R040. Increases in the thermal conductivity followed a
similar pattern as for the density. The increase in thermal
conductivity for concentrations of R040 exceeding 20% was about
0.5% per percent of added RO40. The energy and
displacement-to-failure for the cups was largely unaffected by the
addition of RO40. The peak load increased linearly at the rate of
about 1% per percent of added RO40. The stiffness curve was similar
to the density curve; a relatively flat region up to 20% RO40 and a
linear increase for higher concentrations. The rate of increase in
stiffness was approximately 1% for each percent of added RO40 in
mixtures exceeding 20% RO40.
Based on the above observations, collamyl starch can be used to
make the articles of the present invention. Furthermore, relatively
high concentrations of calcium carbonate can be added to mixtures
containing collamyl starch without significantly reducing the
desired mechanical properties.
Examples 19-26
Cups were made using different types of admixtures to determine
their effects, if any, on the properties of the mixtures. The same
procedures and apparatus set forth in Examples 1-13 were used to
make and test the cups of the present examples. A base mixture was
first prepared by combining the following components by weight:
TABLE-US-00005 39.8% Stalok 400 (modified potato starch) 9.95% RO40
calcium carbonate 49.5% water 0.5% magnesium stearate.
Admixtures, include Methocel.RTM. 240, Tylose.RTM. 15002 and
polyvinyl alcohol (PVA), were then combined to the mixture by
weight percentage of the total solids in the mixture. Summarized
below is a list of the moldable mixtures and the properties
resulting from their use.
TABLE-US-00006 Dis- Ad- Thermal place- Ex- mixtures Den- Conduct.
Energy ment to Peak Stiff- am- (weight sity (W/m to Fail. Failure
load ness ple %) (g/cc) K.) (mJ) (%) (N) (N/m) 19 None 0.26 0.045 4
2.2 4.5 2.8 PVA 20 1.9 0.26 0.046 6 3.1 5.5 2.7 21 2.9 0.27 0.048 5
2.6 5.5 3.3 22 3.4 0.26 0.044 4 2.8 5.0 2.8 Methocel .RTM. 240 23
0.5 0.19 0.045 6 3.4 5.5 2.3 24 1.0 0.18 0.052 8 6.0 4.5 0.9 Tylose
.RTM. 15002 25 0.5 0.23 0.044 7 4.1 5.0 1.8 26 1.0 0.19 0.049 3 3.1
3.5 1.7
The addition of PVA was shown to have little effect on the
densities, thermal conductivities, or mechanical properties of the
cups made therefrom. Methocel.RTM. 240 and Tylose.RTM. 15002
affected the density slightly. The density decreased just over 20%
per each addition of 1% of either admixture. The thermal
conductivity increased about 10% for the same additions.
Methocel.RTM. 240 had a positive effect on the energy and
displacement-to-failure measurements for dry cups. The
energy-to-failure values doubled for each 1% addition, whereas the
displacement-to-failure values showed an improvement of 2.5 times.
The peak load dropped about 20% for each 1% addition of
Methocel.RTM. 240, while the stiffness fell more than 70%. A 0.5%
addition of Tylose.RTM. 15002 increased the energy-to-failure by
60%, the displacement-to-failure by 80% and the peak load by 10%.
These increases disappeared with a further (0.5%) addition of
Tylose.RTM. 15002. The stiffness of dry cups was halved by
additions of 1% of either Methocel.RTM. or Tylose.RTM..
Generally, PVA was found to have a minimal impact on the properties
of the formed cups. Methocel.RTM. 240 and Tylose.RTM. 15002 were
found to either maintain or improve the properties of the cups at
lower concentrations. The benefits, however, were lost as the
concentrations of each was increased.
Examples 27-31
To study the synergistic effect of some admixtures, moldable
mixtures were prepared containing varying amounts of RO40 calcium
carbonate, both with and without the additives Dispex.RTM.A40 and
Methocel.RTM. 240. The same procedures and apparatus set forth in
Examples 1-13 were used to make and test the cups of the following
examples. The cups were made from five different mixtures. Mixture
1 contained the following components by weight: 49.75% water, 0.5%
magnesium stearate, 19.9% RO40 calcium carbonate, and 29.85% Stalok
400 (modified potato starch). Mix 1 further contained 2% Dispex and
0.5% Methocel.RTM. 240 by weight of the combined starch-based
binder and calcium carbonate. Mixture 2 was similar to Mixture 1,
except that the percentage of calcium carbonate was increased to
29.85%, while the starch-based binder was decreased to 19.9%. In
Mixture 3, the calcium carbonate was further increased to 39.8%,
the starch-based binder decreased to 9.95%, and the other
components kept the same as in Mixture 1. Mixture 4 was similar to
Mixture 1, except that Dispex was not added. Finally, Mixture 5 was
similar to Mix 3, except that Methocel.RTM. 240 was not added.
Summarized below are the properties of the cups made from the five
mixtures:
TABLE-US-00007 Dis- Thermal place- Ex- Den- Conduct. Energy ment to
Peak Stiff- am- sity (W/m to Fail. Failure load ness ple Mixture
(g/cc) K.) (mJ) (%) (N) (N/m) 27 Mixture 1 0.23 0.049 5 2.9 4.0 1.7
28 Mixture 2 0.25 0.049 3 2.9 3.0 1.3 29 Mixture 3 0.32 0.057 -- --
-- -- 30 Mixture 4 0.26 0.044 7 3.5 5.5 2.3 31 Mixture 5 0.32 0.052
4 2.1 3.0 2.1
The tests demonstrate that the densities of the articles increased
as the concentration of calcium carbonate was increased. The
densities of the articles increased, however, if either Dispex A40
or Methocel.RTM. 240 was not included in the mix design. The
thermal conductivity exhibited a similar increased with increasing
calcium carbonate concentration. The energy-to-failure and
displacement-to-failure decreased as higher levels of R040 were
included. The samples without Dispex A40 displayed about 30% higher
values, whereas the samples produced from a mixture without
Methocel.RTM. 240 had slightly lower levels of performance. The
peak load and stiffness both exhibited inferior levels when Dispex
A40 and Methocel.RTM. 240 were added to the mixtures.
Although the admixtures were useful in producing articles having
higher concentrations of inorganic aggregates, both Dispex A40 and
Methocel.RTM. 240 produced articles having lower densities and
inferior mechanical properties, perhaps due to their interfering
with the gelation of the unmodified starch binder.
Examples 32-36
Cups were made using different amounts of the crosslinking
admixture Sunrez 747 to determine its effect on the moldable
mixture. The same procedures and apparatus set forth in Examples
1-13 were used to make and test the cups of the following examples.
A base mixture was first prepared by combining the following
components by weight:
TABLE-US-00008 28.15% Stalok 400 (modified potato starch) 19.9%
RO40 calcium carbonate 1.7% PVA 49.75% water 0.5% magnesium
stearate.
The base mixture was then varied by incrementally increasing the
concentration of Sunrez 747 by weight of total solids in the
mixture over a range from 2% to 20%. Summarized below are the
percentages of Sunrez 747 and the corresponding properties of the
resulting cups.
TABLE-US-00009 Dis- Sunrez Thermal place- 747 Den- Conduct. Energy
ment to Peak Stiff- Exam- (weight sity (W/m to Fail. Failure load
ness ple %) (g/cc) K.) (mJ) (%) (N) (N/m) 32 0 0.26 0.044 4 2.8 4.8
2.5 33 2 0.25 0.048 5 2.8 5.0 2.6 34 5 0.24 0.048 4 2.8 4.8 2.5 35
10 0.23 0.048 7 4.4 4.2 1.5 36 20 0.24 0.046 4 3.4 4.0 1.8
The tests showed that Sunrez 747 had limited effect on the cup
density. Initially, the density decreased about 2% for each percent
of added Sunrez 747. This relationship persisted up to about 5% of
the admixture, after which the cup density leveled off. The thermal
conductivity showed an initial increase of approximately 4% for the
first 2% of added Sunrez 747, but then leveled out. The mechanical
properties of the cups also peaked early with the addition of
Sunrez 747.The energy and displacement-to-failure of cups showed
only minor increases up to 10% and then fell off slightly again.
The peak load was fairly level with an apex at 2%. The stiffness
curve approximates a step function. There was a plateau where there
was no effect of Sunrez 747 addition up to 5%. There was a dramatic
decreased in stiffness, roughly 50%, between 5 and 10%; thereafter
the stiffness was not affected. In general, moderate improvements
in the various properties were found where lower concentrations of
Sunrez 747 were added.
Examples 37-44
Five mix designs were evaluated using varying concentrations of
calcium carbonate (RO40), and different types of starch, in order
to determine the minimum processing time and filing weight at four
processing temperatures (160.degree. C., 180.degree. C.,
200.degree. C., and 220.degree. C). As used in the examples,
specification, and appended claims, the term "processing time"
refers to the time necessary to heat the mixture into a form-stable
article. The compositions of the five mixtures were as follows:
TABLE-US-00010 Stalok 400 Hylon VII RO40 Mg Stearate Water (g) (g)
(g) (g) (g) Mixture 1 500 0 0 5 500 Mixture 2 350 50 100 5 450
Mixture 3 300 50 150 5 440 Mixture 4 250 50 200 5 425 Mixture 5 200
50 250 5 410
Hylon VII is a type of modified corn starch that was substituted
for part of the Stalok 400. The moldable mixtures were prepared
using the procedures set forth in Example 1-13. Once the mixtures
were prepared, a HAAS LB-STA machine was used to make 16 oz. cups
having thicknesses of about 4 mm and waffled exteriors. The
resulting filling weights and processing times at the selected
temperatures are summarized as follows:
TABLE-US-00011 Processing Time (sec) Temp. Mixture Mixture Mixture
Mixture Mixture Example (.degree. C.) 1 2 3 4 5 37 220 40 40 40 40
40 38 200 50 50 50 45 45 39 180 75 75 75 75 75 40 160 170 170 170
165 160 Filling Weight (g) Temp. Mixture Mixture Mixture Mixture
Mixture Example (.degree. C.) 1 2 3 4 5 41 220 30.5 32.2 34.4 37.9
41.6 42 200 33 31.5 35.6 39.3 43.9 43 180 31.4 33.5 35.5 37.6 44.1
44 160 31.7 33.7 34.1 39.7 43.9
As expected, the tests revealed that the processing times decreased
as the processing temperatures increased. Although the decrease in
processing time was greatest for increases in processing
temperatures at the lower ranges, the decrease in processing time
was most dramatic where calcium carbonate was included at the
higher concentration ranges. The tests also revealed that the
minimum filling weight increased with higher concentrations of
calcium carbonate. However, the filling weight was independent of
the mold temperature.
Examples 45-49
Using the same process as in Examples 1-13, 12 oz. cups were made
using dies at a temperature of 200.degree. C. The mixture for
manufacturing the cups consisted of the following components by
weight:
TABLE-US-00012 24.95% Stalok 400 (modified potato starch) 19.9%
RO40 calcium carbonate 4.9% Hylon VII (modified corn starch) 49.75%
water 0.5% magnesium stearate.
The dried cups were placed in a high humidity chamber having a
relative humidity of about 95% and a temperature of about
45.degree. C. The cups were removed after varying levels of
moisture had been absorbed by the starch-bound structural matrix of
the cups and tested to determine their mechanical properties. The
respective moisture contents and corresponding mechanical
properties are outlined below:
TABLE-US-00013 BASE MIXTURE-10% Hylon-40% CaCO3 Moisture Peak Load
Displacement to Energy Example Content (N) Failure (%) (mJ) 45 0
5.5 2.9 5 46 2 8.5 3.7 12 47 5.5 10.5 11.8 45 48 7.5 9.0 23.5 65 49
9.5 -- 24.3 40
The test results reveal a roughly linear correlation between the
moisture content and the mechanical properties for low moisture
contents. As the moisture content increased, the mechanical
properties improved.
Examples 50-52
Using the same processing parameters set forth in Examples 1-13, 12
oz. cups were made from moldable mixtures having varying
percentages of calcium carbonate and relatively constant
viscosities to determine the effect of calcium carbonate on the
required water content and time for removing the water. Summarized
below are the compositions tested and the required times to produce
a form-stable article having a finished surface.
TABLE-US-00014 Calcium Starch-based Magnesium Process Carbonate
binder Stearate water Time Example (g) (g) (g) (g) (sec) 50 250 250
10 425 50-55 51 350 150 10 350 35-40 52 400 100 10 285 30
The results show that with increased concentrations of calcium
carbonate, less water was needed to obtain a mixture having a
constant viscosity. Furthermore, as a result of having less water,
the required processing time to produce a form-stable article was
decreased.
Examples 53-59
Articles were made using different types of calcium carbonate to
determine the effect of the particle size and packing density of
the inorganic aggregate. Mixtures were made from three different
types of calcium carbonate. Carbital 75, RO40, and Marblend. The
basic chemical composition for each type of calcium carbonate was
the same; however, the particle size distribution, average particle
size, and natural packing density (or non compressed packing
density), as shown below, varied greatly.
TABLE-US-00015 Type of Calcium Average Particle Size Carbonate
(.mu.m) Natural Packing Density Carbital 75 2.395 0.3593 RO40
40.545 0.6869 Marblend 68.468 0.7368
The gradation for each type of calcium carbonate was as
follows:
TABLE-US-00016 Sieve Opening Retained Passing (.mu.m) % % Gradation
of Carbital 75 18.000 0.00 100.00 5.470 10.00 90.00 3.043 25.00
75.00 1.583 50.00 50.00 0.862 75.00 25.00 0.490 90.00 10.00
Gradation of RO40 275.000 0.00 100.00 134.700 10.00 90.00 82.150
25.00 75.00 41.308 50.00 50.00 14.190 75.00 25.00 2.782 90.00 10.00
Gradation of Marblend 1000.00 0.00 100.00 338.100 10.00 90.00
212.200 25.00 75.00 36.190 50.00 50.00 12.160 75.00 25.00 3.761
90.00 10.00
These tables show that, of the three types of calcium carbonate
tested, Carbital 75 had by far the smallest average particle size
and the smallest particle size distribution. Marblend had the
largest, and RO40 was intermediate. Each mixture contained one type
of calcium carbonate, Stalok 400 potato starch and water, while no
mold releasing agent was used. The mixtures were prepared according
to the procedures set forth in Examples 1-13 and then placed
between molds having a temperature of about 200.degree. C. The
articles were removed from the molds once they had obtained
form-stability. The molds were nickel-Teflon coated and had
complementary shapes defined to produce a platter. The formed
platters were approximately 25 cm long, 18 cm wide, and 3 mm thick.
Outlined below are the components for each mixture, the weight of
the final platter, and the processing time.
TABLE-US-00017 Calcium Platter Processing Carbonate Stalok 400
Water Weight Time Example (g) (g) (g) (g) (sec) Calcium Carbonate
Carbital 75 53 100 900 800 31.6 40 54 200 800 800 32.5 40 55 300
700 800 NA NA Calcium Carbonate RO40 56 700 300 800 30.2 40 57 800
200 800 NA NA Calcium Carbonate Marbland 58 700 300 800 30.2 40 59
800 200 800 NA NA
Examples 53 and 54 produced form-stable articles having negligible
cracks or defects, although the plates of Example 53 were of
somewhat higher quality than those of Example 54. In example 55,
where the Carbital 75 was increased to 30% by weight of the total
solids, crack-free, form-stable articles could not be made,
regardless of the processing time. Examples 56 and 58 produced
form-stable articles having negligible cracks or defects using 70%
by weight of total solids RO40 and Marblend. The best articles were
formed in Example 58. Crack-free, form-stable articles could not be
made in Examples 57 and 59 where the concentration of RO40 and
Marblend was increased to 80% by weight of the solids.
The above examples teach that functional articles can be made with
higher concentrations of inorganic aggregate by using an aggregate
material which (1) has a larger average diameter (which yields an
aggregate material having a lower specific surface area), and (2)
which has a greater particle size distribution (which yields an
aggregate material having a higher particle packing density). The
maximum amount of Carbital 75 that could be used to produce
functional articles was 20% by weight of the solids. In comparison,
functional articles could be made using 70% by weight of either
RO40 or Marblend. The difference in the concentration of aggregate
that could be used is attributed to the fact that RO40 and Marblend
had a natural packing density approximately twice that of Carbital
75. The difference is further attributed to the fact that RO40 and
Marblend had an average particle size that was approximately twenty
to thirty times larger than Carbital 75.
To illustrate, Carbital 75 had a relatively low packing density of
about 0.36. As the concentration of Carbital 75 increased and the
concentration of starch-based binder decreased, respectively, the
volume of interstitial space between the particles increased. As a
result, more of the starch-based binder and water was being used to
fill the interstitial space as opposed to coating the particles.
Furthermore, since the Carbital 75 had a relatively small average
particle size (and, hence, a larger specific surface area), more
water and starch-based binder were needed to coat the aggregate
particles. Eventually, when the concentration of Carbital 75
reached 30% by weight of the solids, the volume of interstitial
space was so large that there was insufficient water to adequately
disperse the starch-based binder and insufficient starch-based
binder to adequately bind the aggregate particles into a
form-stable, crack-free structural matrix.
In contrast, the Marblend had a much higher packing density of
about 0.73 and a larger average particle size. Accordingly, even at
the higher concentration of 70% Marblend by weight of solids, the
interstitial space was sufficiently small to permit the
starch-based binder and water to adequately bind the aggregate
particles into a functional article. At 80% Marblend by weight of
solids, however, the volume of interstitial space was again too
large for the starch-based binder and water to adequately bind the
aggregate particles into a form-stable, crack-free structural
matrix. However, it would be expected that by using an aggregate
having a packing density higher then that of Marblend, an article
could be made having an even higher concentration of inorganic
aggregates.
It is also noteworthy that the viscosity of the mixtures decreased
as the concentration of Carbital 75 increased and that the
viscosity of the mixtures increased with increased concentrations
of RO40 and Marblend. As previously discussed, the starch-based
binder absorbs the solvent. By replacing a portion of the
starch-based binder with an inorganic aggregate, the amount of
solvent that would have been absorbed by the starch-based binder is
free to lubricate the aggregate particles. However, the inorganic
aggregate replacing the starch-based binder also produces
interstitial space which must be filled by the solvent.
Accordingly, if the amount of solvent freed by the removal of the
starch-based binder is smaller than the volume of interstitial
space created by the addition of the aggregate, then the viscosity
of the mixture increases. This process is illustrated by the use of
Carbital 75. In contrast, if the amount of solvent freed by the
removal of the starch-based binder is larger than the volume of
interstitial space created by the addition of more aggregate, then
the viscosity of the mixture decreases. This process is illustrated
by the RO40 and Marblend.
Examples 60-64
In the following examples, each of the components was held constant
except for the starch-based binder, which was gradually substituted
with rice flour. Because rice flour includes a high percentage of
starch, along with some protein, it would be expected to have a
binding effect within the structural matrix. In addition, the inert
fraction would be expected to act as an inert organic filler. All
concentrations are expressed as a percentage by weight of the
overall mixture.
TABLE-US-00018 Magnesium Example Stalok 400 Rice Flour RO40 Water
Stearate 60 24.8% 0% 24.8% 49.5% 0.5% 61 19.8% 5.0% 24.8% 49.5%
0.5% 62 14.9% 9.9% 24.8% 49.5% 0.5% 63 9.9% 14.9% 24.8% 49.5% 0.5%
64 5.0% 19.8% 24.8% 49.5% 0.5%
The compositions of these examples resulted in molded articles in
which the average cell diameter of the cells decreased as the
percentage of the rice flour was increased and the amount of Stalok
400 (potato starch) was decreased. Hence, these examples show that
the cell size can be regulated through the use of controlled
mixtures of starch-based binder of different origin. This, in turn,
results in articles having significantly different physical and
mechanical properties. In this manner, rice flour (or similar grain
flours or alternative starch sources) can be used in varying
amounts in order to carefully control the physical and mechanical
properties of the resulting articles manufactured therefrom. The
following are the average cell diameters and skin thicknesses of
the articles manufactured using the mix designs of these
examples:
TABLE-US-00019 Example Average Cell Diameter Wall Thickness Skin
Thickness 60 670 .mu.m 2.2 mm 300 .mu.m 61 450 .mu.m 2.4 mm 370
.mu.m 62 370 .mu.m 2.5 mm 330 .mu.m 63 300 .mu.m 2.3 mm 350 .mu.m
64 300 .mu.m 2.1 mm 200 .mu.m
Examples 65-68
Moldable mixtures containing varying amounts of polyvinyl alcohol
("PVA") were used to manufacture articles. It was found that the
use of PVA decreased the processing time.
TABLE-US-00020 Starch- based Poly- Exam- binder Calcium Mg vinyl
Process ple (StaLok) Carbonate Stearate Water Alcohol Time 65 500 g
500 g 20 g 883 g 1.7 g 45-50 sec 66 500 g 500 g 20 g 917 g 3.33 g
40-45 sec 67 500 g 500 g 20 g 950 g 5.0 g 40-45 sec 68 500 g 500 g
20 g 983 g 6.7 g 35-40 sec
Examples 69-71
Mixtures were prepared that contained the following components and
concentrations in order to show the effect of solvent concentration
on the density and insulation ability of the articles manufactured
therefrom.
TABLE-US-00021 Potato Starch Calcium Carbonate Magnesium Water
Example (g) RO40 (g) Stearate (g) (g) 69 500 500 10 100 70 500 500
10 200 71 500 500 10 300
The articles manufactured from the mixtures of these examples
demonstrated that using less water resulted in a molded article
having smaller cells, higher density, and lower insulation (higher
thermal conductivity).
Example 72
A study was performed to determine the effect of varying the number
of vent holes within the molding apparatus used to manufacture cups
on the structure of the resulting molded cups. The moldable mixture
of Example 1 was formed into cups using different molding apparatus
in which the number of vent holes was varied so that there were 2,
4, 6, 8, or 10 vent holes of standard size, respectively. The
density of the walls of the resulting cups increased as the number
of vent holes increased, presumably because of the decrease in
pressure that was able to build up, which led to a lower expansion
of the cells within the structural matrix of the cup walls. Hence,
using fewer vent holes results in a molded article having walls
that are less dense and which have larger cells within the
structural matrix.
Examples 73-80
Moldable mixtures are made which have a lightweight aggregate in
order to yield a more lightweight article having greater insulation
ability and lower density. The mixtures used to form such articles
are set forth as follows:
TABLE-US-00022 Perlite (% by Exam- Potato Starch volume of
Magnesium ple (g) mixture) Stearate (g) Water (g) 73 500 5 10 500
74 500 10 10 500 75 500 15 10 500 76 500 25 10 500 77 500 40 10 500
78 500 55 10 500 79 500 65 10 500 80 500 85 10 500
The mixtures are formed into cups using the systems and methods set
forth above. As the amount of perlite is increased, the resulting
cup has a lower density, thermal conductivity, increased stiffness,
and increased brittleness. The cups having the optimal balance of
the foregoing properties are obtained by using a moldable mixture
in which the concentration of perlite ranges from between about 25%
to about 55% perlite by volume of the moldable mixture. However,
using more or less than these amounts may be desired for certain
articles.
In the following group of examples, longer-length fibers were
dispersed within the moldable mixtures by first preparing a
preblended mixture of high viscosity. The result of adding fibers
dramatically increased the fracture energy, toughness, and
flexibility of the newly demolded articles compared to the articles
that were prepared without the use of fibers. In addition, the
articles did not require further conditioning but retained adequate
flexibility due to the remainder of adequate moisture within the
starch-bound cellular matrix, as well as because of the
strengthening effect of the fibers dispersed throughout the
cellular matrix.
Example 81
A moldable mixture for use in forming foamed articles was prepared
having the following ingredients in the respective amounts:
TABLE-US-00023 Potato Starch 500 grams Calcium Carbonate (RO40) 500
grams Softwood Fibers 100 grams Magnesium Stearate 10 grams Water
1300 grams
The moldable mixture was prepared by mixing 100 g of the potato
starch with all of the fibers and 800 g of water to form a
preblended mixture. This preblended mixture was then put into a
microwave oven and heated up above the gelation point of 65.degree.
C. so that the starch would gelate and create a liquid with fibers
suspended therein with a much higher viscosity. The preblended
mixture was then mixed at high shear for 10 minutes resulting is a
complete dispersion of the fibers. The calcium carbonate, and the
remaining amount of starch and water were then added to the
preblended mixture and mixed to form the moldable mixture.
Examples 82-96
Clam shell containers were formed from different moldable mixtures
having five different types of starches and varying water content.
Each of the moldable mixtures of these examples had the following
basic mix design:
TABLE-US-00024 Starch 500 g Calcium Carbonate (RO40) 500 g Softwood
fiber (C33) 100 g Water 900, 1100, 1300 g Magnesium Stearate 20
g
The following starch samples that were utilized in the various
moldable mixtures of these example included Western Polymer (potato
starch), Collamyl 910050, Waxy Corn 7351, Staley Pearl Starch, and
Sta Lok 400 (modified potato starch). The water content of the
moldable mixtures varied at levels of 900, 1100, and 1300 g per 500
g of starch used. The softwood fibers were included at a level of
10% by weight of the combined starch and calcium carbonate. A stock
fibrous sheet comprising individual softwood fibers was broken into
small fragments before being added to the mixture. Colored water
was made by adding 2.55 g Egg Yellow, 0.52 g Blue, and 0.34 g
Double Strength Red, all colors of Iris brand, to 100 g of the
water used in each mixture.
Each of the moldable mixtures of these examples were prepared by
the following procedure. The total 100 g amount of chopped fiber
pieces was soaked in 800 g of the water for about 30 minutes. The
soaked fibers and water were then placed in a mixing bowl of either
a Hobart or Kitchen Aid mixer and mixed at slow to medium speed for
about 4 minutes to form an initial mixture. The mixing action broke
the fibrous sheet fragments into small nodules. A weighed quantity
of 100 g of starch was then added to the initial mixture and the
mixing was continued at medium speed for 1 minute to form a
preblended mixture. The mixer was stopped and the preblended
mixture was placed in a plastic beaker and subjected to microwave
energy in a standard kitchen microwave oven for 10 minutes at high
power in order to gelate the starch. The hot, thickened preblended
mixture was removed from the microwave oven and was shear mixed at
slow, medium and high speeds for a total of 15 minutes to disperse
the fiber therein. Thereafter, 500 g of calcium carbonate, 400 g of
starch and 20 g of magnesium stearate were added to the preblended
mixture, which was mixed at slow to medium speed with additional
water for about 5 minutes so that a final, homogeneous, moldable
mixture was obtained. The additional water included 100 g of
colored water and the remaining water as required in the batch.
The moldable mixtures of these examples were then placed between
male and female molds designed to produce clam shell containers.
The baking time was 75 seconds and the baking temperature of the
female molds was 180.degree. C. and of the male molds was
190.degree. C. The molded clam shell containers were thereafter
removed from the molds.
Summarized below is a list of the selected starches used with the
varying amounts of water in Examples 82-96, as well as the
resulting properties of the clam shell containers formed from each
of the moldable mixtures.
TABLE-US-00025 Water K. Cond. Spec. Shell Content (W/m Thickness
Wt. Moisture Grav. Wt. Example Starch (g) .degree.K.) (mm) (g) (Wt
%) (g/cm.sup.3) (g) 82 Western 900 0.065 1.643 4.360 4.808 0.358
31.44 Polymer 83 Western 1100 0.057 1.660 3.218 3.573 0.300 24.66
Polymer 84 Western 1300 0.063 1.635 3.057 8.906 0.243 20.47 Polymer
85 Collamyl 900 0.064 1.643 3.585 4.549 0.310 27.37 86 Collamyl
1100 0.054 1.593 2.904 4.536 0.251 21.47 87 Collamyl 1300 0.052
1.403 2.414 4.683 0.237 16.03 88 Waxy 900 0.058 1.618 3.342 4.340
0.296 24.59 Corn 89 Waxy 1100 0.053 1.220 2.158 4.302 0.246 15.61
Corn 90 Waxy 1300 0.057 1.543 2.463 4.188 0.229 17.77 Corn 91
Staley 900 0.066 1.663 5.438 4.077 0.458 34.82 Pearl Starch 92
Staley 1100 0.059 1.672 3.106 4.054 0.289 27.32 Pearl Starch 93
Staley 1300 0.061 1.671 3.106 7.251 0.282 22.56 Pearl Starch 94
StaLok 900 0.065 1.317 3.847 5.196 0.409 28.55 400 95 StaLok 1100
0.063 1.311 3.317 4.670 0.350 27.83 400 96 StaLok 1300 0.061 1.640
2.631 4.988 0.219 18.90 400
The properties analyzed for these examples included thermal
properties and mechanical properties. The thermal properties
included thermal conductivity (K). Three measurements were recorded
for the thermal conductivity of the walls of the clam shells and
the average K value was reported. Other properties measured
included the thickness of the formed clam shell walls, the moisture
content, the specific gravity, and the clam shell weight.
As shown above, an increasing amount of water in the moldable
mixture resulted in the specific gravity or density of the formed
clam shell decreasing with an accompanying decrease in gross
weight. Additional properties of the formed clam shells were also
tested, including strength, fracture energy, and strain, which are
listed below.
TABLE-US-00026 Fracture Energy Strain Example Strength (MPa)
(J/m.sup.2) (%) 82 6.2 740 2 83 5.5 780 1.8 84 4.5 650 1.7 85 5.5
600 1.7 86 4.3 620 1.6 87 2.5 430 1.5 88 3.8 500 1.7 89 3 350 1.65
90 2.5 200 1.65 91 11 680 1.85 92 7 550 1.6 93 6 480 1.55 94 5.2
570 2.1 95 4.8 350 1.45 96 4.5 270 1.3
As shown above, as the water content went up and the specific
gravity or density went down the strength decreased from about 11
MPa to about 2.5 MPa, the fracture energy decreased from about 780
J/m.sup.2 to about 200 J/m.sup.2, and the strain decreased from
about 2.1% to about 1.3%.
Examples 97-135
Clam shell containers were formed from different moldable mixtures
having two different types of starches, including Sta Lok 400
potato starch and waxy corn starch, with a varying fiber and water
content. Each of the moldable mixtures of these examples was
prepared according to the procedure described above for Examples
82-96, and were then molded to form clam shell containers.
Summarized below is a list of the fiber amounts of 5, 10, 15, and
20 weight % fiber with varying amounts of water from 800 g to 1500
g used in Examples 97-135, along with the final weight of the
clamshell.
TABLE-US-00027 Example Fiber Content Wt. % Water Content (g) 97 20
900 98 20 1000 99 20 1100 100 20 1200 101 20 1300 102 20 1400 103
20 1500 104 5 800 105 5 900 106 5 1000 107 5 1100 108 5 1200 109 5
1300 110 5 1400 111 5 1500 112 15 800 113 15 900 114 15 1000 115 15
1100 116 15 1200 117 15 1300 118 15 1400 119 15 1500 120 10 800 121
10 900 122 10 1000 123 10 1100 124 10 1200 125 10 1300 126 10 1400
127 10 1500 128 10 800 129 10 900 130 10 1000 131 10 1100 132 10
1200 133 10 1300 134 10 1400 135 10 1500
There was a steady decrease in the weight of the product as the
water content was increased. The weight of the product also
decreased as the fiber content was lowered.
Example 136
Preblended mixtures were prepared having two sample concentrations
in order to determine the effect of starch concentration on the
viscosity and yield stress of the resulting preblended
mixtures:
1. 100 g of Western Polymer potato starch in 800 g of water;
2. 50 g of above starch in 800 g of water.
These mixtures were then microwaved for 10 minutes with frequent
stirring. The stirring was needed to avoid settling of the starch.
A very homogeneous starch gel was obtained in this manner.
On each sample, a single point measurement was made at a shear rate
of 5 s.sup.-1. Sample 1 had a viscosity of 12.5 Pa-s and Sample 2
had a viscosity of 75 Pa-s. The measurements were made on a Paar
Physica MC-20 Rheometer with a cone/plate configuration. The angle
of the cone was 1.degree. with a 0.05 mm truncation. The diameter
of the plate was 50 mm. The single point measurements were double
checked with a 12.5 mm parallel plate.
A flow curve was then generated with a shear rate range of 0-100
s.sup.-1. The measurement included an up-curve over 180 s followed
by a down-curve over 60 s. The down-curve was run to indicate if
there was any permanent effect of shear on the viscosity of the
gel. FIGS. 20 and 21 show graphs of the flow curves for each of
Samples 1 and 2. At both concentrations of Samples 1 and 2, it was
found that the down-curve deviated from the up-curve on the first
measurement, by a small amount. When a second measurement was made
on the same sample of material, this difference disappeared,
indicating a steady state in viscosity. As shown in FIG. 20 for
Sample 1, when the shear rate went up the viscosity went down to a
steady state of about 9 Pa-s. As shown in FIG. 21 for Sample 2,
when the shear rate went up the viscosity went down to a steady
state of about 1.9 Pa-s. FIGS. 22 and 23 show the effect of
pregelatinized starch on the yield stress and viscosity of a liquid
system. The pregelatinized starch increases both the yield stress
and the viscosity dramatically at about 6 weight % and higher.
Examples 137-146
Clam shell containers were formed from different moldable mixtures
having two different types of starches and a varying water content.
Each of the moldable mixtures of these examples was prepared
according to the procedure described above for Examples 82-96, and
were then molded to form clam shell containers.
Summarized below is a list of the selected starches used with the
varying amounts of water, as well as the resulting properties of
the clam shells formed from each of the moldable mixtures.
TABLE-US-00028 Av. Density Av. weight Example Starch Water Cont.
(g) g/cm.sup.3 (g) 137 Western 900 0.338857 31.476 Polymer 138
Western 1100 0.273672 23.545 Polymer 139 Western 1300 0.213098
17.82429 Polymer 140 Western 1500 0.20624 14.75167 Polymer 141
Western 1700 0.156326 11.905 Polymer 142 Staley Pearl 900 0.383888
30.96333 143 Staley Pearl 1100 0.343341 26.93333 144 Staley Pearl
1300 0.218775 17.86333 145 Staley Pearl 1500 0.189838 15.20333 146
Staley Pearl 1700 0.231291 15.40167
As shown above, when the water content in the moldable mixture
increased, average density and weight of the final product
decreased.
Example 147
A viscosity measurement was conducted on a moldable mixture of the
invention on a Paar-Physica instrument. A parallel plate
configuration was used with a gap setting of 1 mm. This unusually
large gap setting was used since the material was very
inhomogeneous, and a large sample was needed for a respective
number. It was determined that the measurements had to be made
quickly and at relatively low shear rates to avoid segregation and
fiber alignment. The viscosity was found to be 446 Pa-s (or 446,000
cps) at 5 s.sup.-1. This number was an average of three single
point measurements that varied between 419 and 472 Pa-s.
FIGS. 24 and 25 show flow curves for a composition of the present
invention. FIG. 24 shows a drop in viscosity with increasing shear
rates, and FIG. 25 shows a drop in viscosity with time. This is
most likely due to the alignment of fibers in the direction of
shear.
FIG. 26 is a graph of the skin thickness as a function of water
content for a formed product of the invention, showing that as the
water content increased in the moldable mixture, the skin thickness
decreased in the final product. FIG. 27 is a graph of the average
internal cell diameter as a function of water content for a formed
product of the invention, showing that as the water content
increased the cell diameter also increased.
The present invention may be embodied in other specific forms
without departing from its spirit or essential characteristics. The
described embodiments are to be considered in all respects only as
illustrated and not restrictive. The scope of the invention is,
therefore, indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalency of the claims are to be embraced within
their scope.
* * * * *