U.S. patent application number 10/752474 was filed with the patent office on 2004-07-22 for method for manufacturing cellulose fiber reinforced composites having reduced discoloration and improved dispersion.
This patent application is currently assigned to Rayonier Products and Financial Services Company. Invention is credited to Barlow, Fred, Khanna, Yash, Pietsch, Daren B., Underwood, John.
Application Number | 20040140592 10/752474 |
Document ID | / |
Family ID | 29710449 |
Filed Date | 2004-07-22 |
United States Patent
Application |
20040140592 |
Kind Code |
A1 |
Barlow, Fred ; et
al. |
July 22, 2004 |
Method for manufacturing cellulose fiber reinforced composites
having reduced discoloration and improved dispersion
Abstract
The present invention provides composites prepared from melt
blending compositions that generally include cellulosic pulp fibers
having an alpha-cellulose purity of greater than 80% by weight, at
least one water soluble binder, at least one lubricant, at least
one compatibilizer, and at least one matrix polymer. The present
invention further provides advantageous temperature profiles and
feeding arrangements to be used in conjunction with the melt
blending of such composites. The composites of the present
invention exhibit reduced discoloration and improved fiber
dispersion.
Inventors: |
Barlow, Fred; (St. Simons
Island, GA) ; Khanna, Yash; (Brunswick, GA) ;
Pietsch, Daren B.; (St. Simons Island, GA) ;
Underwood, John; (St. Simons Island, GA) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
Rayonier Products and Financial
Services Company
|
Family ID: |
29710449 |
Appl. No.: |
10/752474 |
Filed: |
January 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10752474 |
Jan 6, 2004 |
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10165502 |
Jun 7, 2002 |
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6743507 |
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Current U.S.
Class: |
264/523 ;
264/136; 264/137; 264/211; 264/310; 264/319; 264/328.18 |
Current CPC
Class: |
Y10T 428/249948
20150401; C08L 1/00 20130101; C08L 2666/26 20130101; B29C 48/022
20190201; C08J 5/045 20130101; C08J 2323/02 20130101; C08L 23/0869
20130101; Y10T 428/2938 20150115; C08L 1/08 20130101; C08L 23/10
20130101; C08L 101/00 20130101; C08L 2666/26 20130101; Y10T
428/2964 20150115; C08L 23/02 20130101; Y10T 428/2965 20150115;
B29K 2711/14 20130101; C08L 1/00 20130101; C08L 23/10 20130101;
Y10T 428/24994 20150401; B29C 48/405 20190201; C08L 23/02 20130101;
B29K 2201/00 20130101; C08L 33/26 20130101; C08L 101/00 20130101;
C08L 2205/08 20130101; Y10T 428/2913 20150115; B29K 2105/06
20130101; Y10T 428/2933 20150115; Y10T 428/2967 20150115; B29B 7/92
20130101; B29C 48/40 20190201; B29C 48/04 20190201; C08L 51/06
20130101; Y10T 428/249924 20150401; C08L 2203/12 20130101; B29B
7/48 20130101; C08L 91/00 20130101; C08L 2666/26 20130101; C08L
2203/12 20130101; C08L 2666/26 20130101 |
Class at
Publication: |
264/523 ;
264/211; 264/328.18; 264/310; 264/136; 264/137; 264/319 |
International
Class: |
B29C 049/00; B29C
043/02; B29C 045/00; B29C 041/04; B29C 047/00 |
Claims
That which is claimed:
1. A process for the manufacture of composites containing
cellulosic pulp fibers dispersed in a matrix polymer, said process
comprising: (A) providing a melt blending composition including
cellulosic pulp fibers having an alpha-cellulose purity of greater
than 80% by weight and at least one matrix polymer exhibiting a
melting point of less than about 200.degree. C. and a melt flow
index ranging from about 0.10 to 100 to a main feed throat of a
compounding extruder including at least three heated regions and a
heated die; and (B) compounding said melt blending composition by
transporting the melt blending composition through each of the
heated regions and the die, which include (i) an initial region
heated to a temperature of about 10 percent below the matrix
polymer melting point; (ii) a first intermediate region heated to a
temperature of about 15 to 20 percent below the matrix polymer
melting point; (iii) a second intermediate region heated to a
temperature of about 15 to 20 percent above the matrix polymer
melting point; and (iv) a die heated to a temperature of about 35
to 40 percent above the matrix polymer melting point.
2. A process according to claim 1, further comprising introducing
an additional amount of said matrix polymer into a secondary feed
throat positioned downstream of said main feed throat and upstream
of the second intermediate region.
3. A process according to claim 2, wherein the amount of cellulosic
pulp fibers within the melt blending composition is greater than 30
weight percent, based on the weight of the melt blending
composition, and the amount of matrix polymer introduced into the
secondary feed throat is selected to provide a composite containing
30 weight percent cellulosic pulp fibers.
4. A process according to claim 2, wherein the additional amount of
matrix polymer exhibits a melt flow index that is substantially
lower than the melt flow index of the matrix polymer introduced
into the main feed throat.
5. A process according to claim 4, wherein the additional amount of
matrix polymer exhibits a melt flow index ranging from about 10 to
25 and the melt flow index of the matrix polymer introduced into
the main feed throat ranges from about 30 to 90.
6. A process according to claim 4, wherein the additional amount of
matrix polymer exhibits a melt flow index ranging from about 10 to
12 and the melt flow index of the matrix polymer introduced into
the main feed throat ranges from about 50 to 80.
7. A process according to claim 1, wherein said cellulosic pulp
fibers and said matrix polymer are present in said melt blending
composition at fiber to matrix polymer weight ratios ranging from
about 30 to 70 to about 80 to 20.
8. A process according to claim 1, wherein said cellulosic pulp
fibers and said matrix polymer are present in said melt blending
composition at fiber to matrix polymer ratios ranging from about 45
to 55 to about 60 to 40.
9. A process according to claim 1, wherein the matrix polymer is
polypropylene.
10. A process according to claim 1, wherein the matrix polymer is
polypropylene and (a) the initial region is heated to a temperature
of about 125 to 142.degree. C. (b) the first intermediate region is
heated to a temperature ranging from about 115.degree. C. to
135.degree. C.; (c) the second intermediate region is heated to a
temperature of about 160 to 190.degree. C. and (d) the die is
heated to a temperature of about 190 to 220.degree. C.
11. A process according to claim 1, further comprising: (a)
preparing a molding composition incorporating the compounded
composition; and (b) forming the molding composition into a molded
article.
12. A process according to claim 11, wherein said forming step is
selected from injection molding, compression molding, blow molding,
rotational molding, extrusion and pultrusion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/165,502, filed Jun. 7, 2002, which is hereby incorporated
herein in its entirety by reference.
FIELD OF THE INVENTION
[0002] This invention relates to composite materials containing
cellulosic pulp fibers dispersed in a polymeric matrix. The
invention also relates to methods by which to produce such
composites and molded articles therefrom.
BACKGROUND OF THE INVENTION
[0003] Composites are widely used in a broad spectrum of
applications, including automotive parts, sporting goods, computer
chips, and the like. Composites are generally defined as a
macroscale combination of two or more solid components that are
insoluble in each other and which further differ in chemical
nature. More particularly, composites typically include at least
one reinforcing component enveloped in a matrix composition. The
reinforcement generally bears the load to which the composite is
subjected, while the matrix transfers the load between the
reinforcing elements. An interface is formed between the
reinforcement and the matrix. It is the adhesion between the two
constituents at this interface which determines the mechanical
properties of the composite as a whole. In fact, adhesion is
responsible for the generally synergistic nature of composites. For
example, the adhesion developed within composites can provide
mechanical properties that are generally superior to the mechanical
properties of the individual elements, either alone or in
combination. In addition to mechanical properties, composites
possessing adequate adhesional characteristics can also provide
other physical properties, such as conductivity, notched impact
resistance, and the like, which are superior to the sum of the
properties of the individual components. A number of factors impact
the adhesion developed within composites, including the dispersion
of the reinforcement component within the matrix and the level of
compatibility between the reinforcement and the various components
which make up the matrix compositions. Coatings may be applied to
the reinforcement to promote adhesion, such as the acrylate graft
copolymers described in U.S. Pat. No. 4,131,577. However, there
nevertheless remains in the art a need for composites exhibiting
improved adhesion. There further remains a need in the art for
composites having other improved propeties, such as color and the
like. A variety of polymers, both thermoset and thermoplastic,
commonly serve as the basis for the matrix composition.
Thermoplastic polymers are particularly attractive for use in
matrices, due to their ease of processability. Well known
thermoplastic matrix materials include polyamides, such as nylons,
polyesters, and polyolefins, particularly polypropylene.
Polypropylene is a particularly attractive matrix material for
applications requiring performance at low to moderate temperatures
because it is relatively inexpensive and light weight, yet provides
adequate physical properties. Consequently, polypropylene is
regularly used as the matrix polymer in automotive composites, such
as injection molded interior parts and the like.
[0004] Numerous fibrous materials are similarly known for use as
reinforcements in composites. Glass fibers are particularly widely
used as the reinforcing component for composites, imparting
increased mechanical strength, dimensional stability, and heat
resistance to the final composite. However, although glass fibers
achieve desirable reinforcing properties, they are fairly costly,
abrade processing equipment and increase the overall density of the
composite. In certain applications, these disadvantages outweigh
the advantages of using glass fibers as a reinforcement
component.
[0005] Cellulosic materials have been evaluated as fibrous
reinforcements for composites in the past. Klason, et al.,
"Cellulosic Fillers for Thermoplastics", Polymer Composites,
(1986); Klason, et al., "The Efficiency of Cellulosic Fillers in
Common Thermoplastics. Part 1. Filling without processing aids or
coupling agents", Intern. J. Polymeric Mater., Volume 10, pgs.
159-187 (1984); Snijder, et al., "Polyolefins and Engineering
Plastics Reinforced with Annual Plant Fibers", The Fourth
International Conference on Wood Fiber-Plastic Composites, pg.
181-191.
[0006] Cellulosic materials are especially attractive for use in
composites because they have relatively low densities. For example,
cellulose fibers have a density of approximately 1500 kg/m.sup.3 in
comparison to a density of 2500 kg/m.sup.3 for E grade glass
fibers. Such weight savings can be highly advantageous,
particularly in automotive applications. In addition to the
reduction in weight, cellulosic fibers are not abrasive to
processing equipment in comparison to glass fibers or high density
mineral fibers, e.g. wollastonite.
[0007] However, prior investigations into the use of cellulosic
materials, e.g. cellulose pulps or raw lignocellulosic resources
(e.g., wood flour, bagasse), in polymeric materials found that a
pronounced discoloration of the composite material occurred if the
cellulose materials were processed at elevated temperatures, such
as the temperatures commonly employed when melt blending the
reinforcement and matrix. Furthermore, cellulosic materials were
found to cause significant off-gasing and objectionable odors.
These disadvantageous results directed previous research efforts to
the use of cellulosic materials in matrix polymers having more
moderate melting temperatures, such as melting temperatures of
below 200.degree. C. Further, the use of cellulosic fibers having
higher alpha-cellulose contents has been proposed in conjunction
with higher melting matrix polymers, as discussed in U.S. Pat. No.
6,270,883 hereby incorporated by reference in its entirety.
[0008] However, despite such research efforts, discoloration
continues to be problematic in conventional cellulosic
material-reinforced composites prepared from matrices having even
moderate melting temperatures. For example, an undesirable brownish
discoloration is observed in conventional composites formed from
cellulose fibers dispersed in a polyolefinic matrix. As noted
above, this brownish discoloration is generally associated with the
degradation of the cellulose fibers during processing and often
gives rise to malodors during product usage. Further, an
unacceptable level of fiber agglomeration has been observed in
conventional cellulosic fiber/polyolefin composites to date. As
noted previously, such agglomeration would be expected to be
detrimental to the interfacial adhesion characteristics of the
composite, thus negatively impacting mechanical properties and the
like. Further, agglomeration of the cellulosic fibers can give rise
to surface roughness and non-uniform properties. Consequently, a
need exists in the art for cellulose-reinforced composites having
improved color and dispersion properties.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention provides improved cellulosic fiber
reinforced composites and methods by which to form such composites.
More specifically, the present invention provides cellulosic fiber
reinforced composites having a beneficial balance of matrix
components selected to impart improved color and fiber dispersion
characteristics to the resulting composite. The present invention
further provides methods by which to produce cellulosic fiber
reinforced composites having superior color and fiber dispersion in
comparison to known cellulosic material reinforced composites.
[0010] The cellulosic fiber reinforced composites of the present
invention further provide improved structural characteristics to
the matrix material at a reduced cost in comparison to conventional
glass fibers and with a much lower increase in the density of the
resulting composite. The cellulosic pulp fibers employed in the
composites of the invention also do not significantly abrade the
processing equipment or generate malodors during composite
manufacture. Additionally, the use of the cellulosic pulp materials
according to the invention allows for the blending of the
components and molding of the resultant composite material at lower
processing temperatures.
[0011] In one advantageous embodiment, cellulose reinforced
composites are provided that are prepared from a melt blending
composition that includes: cellulosic pulp fibers having an
alpha-cellulose purity of greater than about 80% by weight; at
least one olefinic matrix polymer; at least one water soluble
binder; at least one lubricant; and at least one compatibilizer.
Exemplary water soluble binders include polyacrylamide, sodium
carboxymethyl cellulose polyvinyl alcohol, polyethylene glycol and
mixtures thereof. Exemplary lubricants for use in the present
invention include silicone oil, ethylene bisstearamid, metal
stearates, fatty acid amides, and mixtures thereof. In one
beneficial embodiment, the lubricant is a mixture of silicone oil
and ethylene bisstearamid. Exemplary compatibilizers for use in the
invention include maleated polypropylene, maleated co- or
ter-polymers of ethylene and mixtures thereof. Suitable olefinic
matrix polymers include polypropylene, polyethylene, polybutene,
polyisobutene, poly(methyl pentene), copolymers thereof,
terpolymers thereof and mixtures thereof. The melt blending
composition may further include at least one coupling agent
selected from silanes, titanates, zirconates, and mixtures
thereof.
[0012] Another aspect of the invention provides processes for the
manufacture of composites containing cellulosic pulp fibers
dispersed in an olefinic matrix polymer. Such processes generally
include introducing a melt blending composition into the main feed
throat of a compounding extruder and transporting the melt blending
composition through at least three heated regions and a heated die
within the extruder, in which an initial region of the compounding
extruder is heated to a temperature of about 10 percent below the
matrix polymer melting point; a first intermediate region of the
compounding extruder, which may constitute a major region of the
extruder, is heated to a temperature of about 15 to 20 percent
below the matrix polymer melting point; a second intermediate
region of the compounding extruder, e.g., a small region
immediately preceding the die, is heated to a temperature of about
15 to 20 percent above the matrix polymer melting point; and the
die is heated to a temperature of about 35 to 40 percent above the
matrix polymer melting point. In further beneficial aspects, an
additional amount of olefinic matrix polymer is introduced into a
secondary feed throat of the compounding extruder positioned
downstream of the main feed throat. In additional advantageous
embodiments of these aspects, the olefinic matrix polymer
introduced into the secondary feed throat possesses a melt flow
index that is substantially lower than the melt flow index of the
olefinic matrix polymer introduced into the main feed throat.
[0013] The present invention further provides molded articles
prepared from melt blending compositions including cellulosic pulp
fibers having an alpha-cellulose purity of greater than about 80
percent by weight; at least one water soluble binder; at least one
lubricant; at least one compatibilizer; and at least one matrix
polymer. Molded articles in accordance with the present invention
include injection molded articles, compression molded articles,
blow molded articles, rotational molded articles, extruded articles
and pultruded articles.
[0014] Further understanding of the processes and systems of the
invention will be understood with reference to the drawings and
detailed description which follows herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0016] FIG. 1 represents a flow diagram of a typical manufacturing
process used to prepare articles in accordance with one embodiment
of the present invention.
[0017] FIG. 2 is a schematic drawing of a compounding extruder in
accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0019] The present invention relates to cellulose reinforced
composites formed from cellulosic pulp fibers that are dispersed in
a matrix composition that generally includes at least one matrix
polymer, at least one water soluble binder, at least one lubricant,
and at least one compatibilizer.
[0020] As noted previously, the cellulosic pulp fibers impart
reinforcing properties to the composites of the invention. The
cellulosic pulp fibers generally exhibit an alpha-cellulose purity
of greater than about 80% by weight. In advantageous embodiments,
the cellulosic pulp fibers may have an alpha-cellulose purity
greater than about 90% by weight. In further beneficial aspects of
these embodiments, the cellulosic pulp fibers may have an
alpha-cellulose content of greater than about 95% by weight, such
as an alpha-cellulose content of greater than about 96% by weight,
and advantageously greater than 98%.
[0021] The cellulosic pulp fibers may further beneficially possess
low amounts of residual lignin. For example, the cellulosic pulp
fibers can have a lignin content less than about 2% by weight, such
as lignin contents of less than about 1% by weight or less than
about 0.5% by weight.
[0022] Exemplary cellulosic pulps from which to extract fibers
include TERRACEL.TM.-10J, ULTRANIER.TM.-J, RAYFLOC.TM.-J-LD,
POROSANIER.TM.-J-HP, ETHENIER.TM.-F-UHV, SULFATATE.TM.-H-J-HD and
PLACETATE.TM.-F pulps, each of which are commercially available
from Rayonier, Performance Fibers (Jesup, Ga.). All of these pulps
have an alpha-cellulose purity of about 95% or greater with the
exception of RALFLOC.TM.-J, which has alpha-cellulose content of
about 86%. All are softwood pulps with the exception of
TERRACEL.TM.-10J and SULFATATE.TM.-H-J which are manufactured from
hardwood fibers. The PLACETATE.TM. and ETHENIER.TM. grades are
sulfite pulps whereas the others are kraft pulps.
[0023] Further exemplary cellulosic pulps include ESTERCELL.TM. and
VISCOCELL.TM. (International Paper--Natchez, Miss.), SUPERSOFT.TM.
(International Paper--Texarkana, Tex.), BORREGAARD UHV-S.TM.
(Borregaard, Sarpsborg, Norway), SAICCOR ACETATE.TM. and SAICCOR
VISCOSE.TM. (Saiccor-Umkomass, South Africa), Weyerhaeuser MAC
II.TM. (Weyerhaeuser, Cosmopolis, Wash.), Buckeye A-5.TM. and
Buckeye COTTON LINTERS.TM. (Buckeye Technologies--Perry, Fla. and
Memphis, Tenn., respectively).
[0024] The cellulosic pulp fibers may be derived from either a
softwood pulp source or hardwood pulp source or mixtures thereof.
Exemplary softwood pulp sources include trees such as various pines
(Slash pine, Loblolly pine, White pine, Caribbean pine), Western
hemlock, various spruces, (e.g., Sitka Spruce), Douglas fir and/or
mixtures of same. Exemplary hardwood pulp sources include trees
such as sweet gum, black gum, maple, oak, eucalyptus, poplar,
beech, and aspen or mixtures thereof.
[0025] The cellulosic pulp fibers may be of any length that is
sufficient to impart suitable reinforcing properties to the
resulting composite. In advantageous embodiments, the cellulosic
fibers are characterized by an average length, e.g., a weighted
average fiber length ("WAFL") length, between about 0.1 to 6 mm. In
advantageous aspects of the invention the average fiber length is
around 0.8 mm. In alternative beneficial aspects, the cellulose
fibers are characterized by an average length of about 1.8.
Advantageously, the cellulosic pulp fibers of the present invention
are not coated with a graft copolymer.
[0026] The composite typically includes from about 1% to 75% by
weight cellulosic pulp fibers, such as between about 10 to 75% by
weight cellulosic fibers. In beneficial embodiments, the composites
of the present invention include less than about 60% by weight
cellulosic pulp fibers, such as composites including less than
about 40% by weight cellulosic pulp fibers. In advantageous aspects
of these beneficial embodiments the composites of the present
invention include cellulosic pulp fibers in an amount of about 30
to 35% by weight.
[0027] The matrix composition generally includes a number of
components, including at least one matrix polymer. Any
thermoplastic polymer exhibiting a melting temperature of less than
about 200.degree. C. may advantageously be employed as the matrix
polymer. Melting temperatures of less than about 200.degree. C. are
particularly common for olefinic polymers. Exemplary olefinic
polymers for use as the matrix polymer include polypropylene,
polyethylene, poly (1-butene), polyisobutene, poly (1-pentene),
poly(3-methyl-1-pentene), poly (4-methyl-1-hexene), poly
(5-methyl-1-hexene), copolymers thereof, terpolymers thereof, and
mixtures thereof. As used herein, the term "polyethylene" includes
high density, medium density, low density, linear low density,
ultra high density and medium low density polyethylene.
Advantageously, the olefinic matrix polymer may be polypropylene,
polyethylene or a mixture thereof. In an alternative embodiment,
the thermoplastic polymer may be polyamide 11, polyamide 12 or a
mixture thereof. Polyamide 11 and polyamide 12 have melting points
of 186.degree. C. and 177.degree. C., respectively.
[0028] The melt flow index of the olefinic polymer, e.g.
polypropylene, is generally selected to provide acceptable
processability. For example, the olefinic polymer melt flow index
may typically range from about 0.1 to 100. In advantageous aspects,
the melt flow index of the olefinic matrix polymer can range from
about 10 to 25, such as a melt flow index ranging from about 10 to
12. In further beneficial aspects of the invention, higher
molecular weight olefinic matrix polymers may be employed, such as
olefinic polymers exhibiting a melt flow index ranging from about
4.0 to 35.
[0029] In alternative embodiments, the olefinic matrix polymer may
include a mixture of polymer having different melt flow indices. In
such embodiments, a first portion of the olefinic matrix polymer
may possess a relatively high melt flow index, such as a melt flow
index ranging from about 30 to 90, while a second portion of the
olefinic matrix polymer may exhibit a significantly lower melt flow
index, such as a melt flow index ranging from about 10 to 25. In
beneficial aspects, the melt flow index of the first portion may
range from about 50 to 80, and more specifically from about 70 to
80. In further advantageous aspects, the melt flow index of the
second portion may range from about 10 to 12. The mixture of
olefinic polymer having different melt flow indices may further be
a mixture of the same type of olefinic polymer, e.g. a mixture of
lower and higher melt indices polypropylene, or different types of
olefinic polymers, e.g. a mixture of higher melt index
polypropylene and lower melt index polyethylene.
[0030] The composite typically includes from about 25% to 99% by
weight matrix polymer, such as between about 25 to 70% by weight
matrix polymer. In beneficial embodiments, the composites of the
present invention include more than about 50% by weight matrix
polymer, such as composites including more than about 40% by weight
matrix polymer. In advantageous aspects of these beneficial
embodiments the composites of the present invention include matrix
polymer in an amount of about 65 to 70% by weight.
[0031] The matrix composition may further include at least one
water soluble binder. The water soluble binder generally provides
integrity to the cellulose pulp fibers during intermediate
processing stages (as will be described in greater detail below).
The water soluble binder is further believed to aid in dispersing
the cellulosic pulp fibers within the matrix polymer. Any polymer
having sufficient hydrophilicty to impart water solubility and
exhibiting a molecular weight ranging from about 50.times.10.sup.3
to 25.times.10.sup.6 Daltons, may be employed. Exemplary water
soluble binders include a variety of polymers, such as
polyacrylamide, polyacrylic acid, polyvinyl alcohol, polyethylene
glycol, and poly(n-vinylpyrroliddinone) and mixtures thereof.
Further suitable water soluble binders include salt substituted
celluloses, such as sodium carboxymethyl cellulose, sodium
hydroxyethylcellulose, sodium carboxymethylhydroxyethylcellulose,
sodium hydroxypropylcellulose and the like, as well as mixtures
thereof.
[0032] Although not wishing to be bound by any theory, applicants
hypothesize that thermoplastic water soluble binders may provide
both improved thermal stability during composite manufacture and
greater compatibility with the cellulose pulp fibers in comparison
to cellulose based water soluble binders. Applicants further
theorize that the combination of increased thermal stability and
greater compatability provided by water soluble binders may impart
better color and fiber dispersion to the resulting composite.
Consequently, in beneficial aspects of the invention thermoplastic
water soluble binders are employed. In one advantageous embodiment
of these aspects, polyacrylamide is employed as the water soluble
binder.
[0033] The water soluble binder may be present in any amount
effective to provide adequate integrity to the cellulosic fibers
during processing and/or to impart adequate dispersion properties.
For example, the water soluble binder may beneficially be present
within the composite in amounts ranging from about 0.01 to 3 weight
percent, such as in amounts ranging from about 0.01 to 2.0 weight
percent based on the weight of the cellulosic pulp fibers. In
advantageous embodiments, the water soluble binder is present in
the composite in an amount of about 0.5 weight percent, based on
the weight of the cellulosic pulp fibers.
[0034] Advantageously, the water soluble binder is capable of
producing high viscosity solutions. The water soluble binder is
typically characterized by a molecular weight in excess of 50,000.
In one advantageous aspect of the invention, the water soluble
binder exhibits a molecular weight of about 15.times.10.sup.6
daltons.
[0035] The water soluble binder may optionally include an effective
amount of a softener, such as a non-ionic surfactant. The softener
is believed to act as a debonding agent to facilitate the
dispersion of the pulp fiber mass. One exemplary softener is
BEROCELL.TM. 509, commercially available from Eka Chemicals, Paper
Chemicals Division. The softener may be included in exemplary
amounts ranging from about 0.1 to 2.0% weight percent, based on the
weight of the cellulose pulp fiber. In one beneficial embodiment,
the softener is present in an amount of about 0.5 weight percent,
based on the weight of the cellulose pulp fiber.
[0036] The matrix composition may further include at least one
lubricant. The lubricant is generally believed to provide improved
fiber dispersion within the composite, as well as reduced
discoloration via reduced frictional degradation during
compounding. Although not wishing to be bound by theory, Applicants
hypothesize that the lubricant, and potentially the water soluble
binder decreases the number of fiber clumps within the composite.
For example, the cellulosic pulp fibers of the invention may
advantageously be dispersed substantially evenly throughout the
entire composite. This reduction in cellulose fiber clumping will
require less shear energy during composite manufacture, thereby
contributing to the improved color and dispersion properties of the
present invention. Such improved fiber dispersion would further be
expected to provide more uniform properties, such as mechanical
properties and the like, across the cross section of the resulting
composite. However, although believed to impart a host of
beneficial properties to the present invention, lubricants are
generally considered to be detrimental to adhesion. More
specifically, lubricants are known for use as release agents to
eliminate the adhesion between surfaces. Consequently, it is
altogether unexpected that the inclusion of suitable amounts of
lubricants enhance the optical and fiber dispersion characteristics
of the present invention without substantial detriment to the
remaining physical properties.
[0037] Any compound which is compatible with both the matrix
polymer and cellulosic fibers, is thermally stable during composite
processing and further provides lubricating properties to the
fibers may be employed as the lubricant. The lubricant
advantageously exhibits minimal weight loss, e.g. less than 5%, at
temperatures of up to about 260.degree. C. Exemplary lubricants
include silicone oil, fatty amides, such as ethylene bisstearamid
and oleyl palmitamide, metal sterates and mixtures thereof. In one
advantageous embodiment, silicone oil is employed as the lubricant.
In an alternative advantageous embodiments, the lubricant is a
mixture of silicone oil and a fatty amide. More particularly, the
lubricant may beneficially be a mixture of silicone oil and
ethylene bisstearamid, such as mixture including silicone oil and
ethylene bisstearamid in about a 2:1 weight ratio.
[0038] In beneficial embodiments liquid lubricants are employed, as
it is hypothesized that liquid lubricants can be better dispersed
throughout the fiber bundles. The lubricants may also beneficially
have a molecular weight ranging from about 10,000 to 80,000
daltons. In advantageous embodiments of these aspects, lubricants
characterized by a molecular weight ranging from about 15,000 to
60,0000 daltons, such as lubricants exhibiting a molecular weight
of about 30,000 to 50,000 daltons, may be employed. In more
specific beneficial embodiments of the invention, lubricants
including silicone oil exhibiting such molecular weight ranges are
employed.
[0039] The lubricant may be present in any amount sufficient to
impart adequate dispersion and/or release properties to the
resulting composite. In advantageous embodiments, the lubricant is
present in an amount ranging from about 0.3 to 5.0 weight percent,
such as an amount ranging from about 0.3 to 3.0 weight percent,
based on the weight of the composite. In one aspect of these
embodiments, the lubricant is present in an amount of about 1.0
weight percent, based on the weight of the composite.
[0040] A compatibilizer may also be incorporated into the matrix
compositions of the present invention. Although not wishing to be
bound by theory, the compatiblizer is believed to improve the
adhesion between the matrix polymer and the cellulosic fibers by
reducing the hydrophilic/hydrophobic differences which exist
between them. Applicants have thus determined that certain
compounds may act as bridging agents between the cellulosic
reinforcing fibers and hydrophobic matrix polymers. Applicants
further hypothesize that specific compounds may have greater
compatibility within specific matrix polymer/cellulose fiber
combinations.
[0041] Any compound providing suitable adhesive properties to the
resulting composite may be employed as a compatibilizer. Exemplary
compatibilizers include maleated polypropylene and maleated
copolymers or terpolymers of ethylene and mixtures thereof. In
beneficial aspects of the invention, maleated polypropylene is
employed, particularly in conjunction with olefinic matrix
polymers. One exemplary maleated polypropylene includes about 99%
polypropylene and 1% maleic anhydride polymer. One maleated
polypropylene suitable for use in the present invention is
commercially available as POLYBOND.TM. 3200 from Crompton
Corporation.
[0042] The compatibilizer may be present within the cellulose
reinforced composite in any amount effective to provide sufficient
bonding between the cellulose pulp fibers and the matrix polymer.
Suitable amounts of compatibilzer include amounts ranging from
about 0.1 to 5 weight percent, based on the weight of the
composite. In advantageous embodiments, the compatibilizer may be
incorporated into the cellulose-reinforced composite in an amount
of about 2 weight percent, based on the weight of the
composite.
[0043] One or more coupling agents may also be included within the
matrix composition. Exemplary coupling agents include titanates,
zirconates, silanes, and mixtures thereof. In one advantageous
embodiment, the coupling agent is derived from silane. The coupling
agent may typically be included in the composite in amounts ranging
from about 0.1 to 5 weight percent, based on the weight of the
composite. In advantageous embodiments, the coupling agent may be
incorporated into the cellulose-reinforced composite in an amount
of about 2 weight percent, based on the weight of the
composite.
[0044] One or more antioxidants may also be included within the
matrix composition. Exemplary antioxidants include hindered phenols
and mixtures thereof. Exemplary antioxidants include Irgafos 168
from Ciba Geigy and Naugard B25 from Uniroyal Chemical. The
antioxidant may typically be included in the matrix composition in
amounts ranging from about 0.1 to 0.3 weight percent, based on the
weight of the composite. In advantageous embodiments, the
antioxidant may be incorporated into the cellulose-reinforced
composite in an amount of about 0.3 weight percent, based on the
weight of the composite.
[0045] FIG. 1 schematically illustrates the typical three step
process used to produce articles in accordance with the present
invention. The process generally includes a fiber preparation step,
a melt blending step and a molding step. The primary purpose of the
fiber preparation step is to transform the cellulosic pulp fibers
into a form suitable for feeding into the compounding extruder for
melt blending with the matrix composition. The melt blending step
is generally used to disperse the separated fibers within the
matrix composition. A molding step is then typically used to impart
a suitable three dimensional shape to the composite.
[0046] As used herein, the term "composite" refers to the
intermediate composite exiting the melt blending step, although the
finished article exiting the molding step could similarly be
characterized as a "composite," as both contain reinforcing fibers
dispersed in a matrix composition. Consequently, for the sake of
clarity, the intermediate composite may be referred to at times as
"blended chip" and the subsequent molded product may be referred to
at times as an "article" within the remainder of the
specification.
[0047] As noted above, the primary purpose of the fiber preparation
step is to produce cellulosic pulp fibers in a form suitable for
melt blending with the matrix polymer. Commercial cellulosic pulps
are typically available as either cut sheets or sheet rolls.
Consequently, to facilitate feeding and blending of the fibers with
the matrix polymer, the incoming cellulose pulp fibers need to be
of a form that can be efficiently fed into the extruder and melt
blended with the matrix polymer. Pelletization and granulation are
methods to produce suitable forms of cellulose pulp fibers for this
use. In order to properly pelletize or granulate cellulose pulp
fibers, separate individual fibers or small aggregates of fibers
are required. Separate individual fibers or small aggregates of
fibers may be obtained either prior to sheeting the cellulose pulp
fibers or by defiberizing sheeted material.
[0048] Granulation is generally performed using a rotary knife
cutter to break up the cellulosic pulp fibers within the incoming
pulp sheets or rolls. Unfortunately, the granulation process
typically reduces the average fiber length. This decreased
cellulose fiber length typically translates into decreased physical
properties in the resulting composite.
[0049] In an alternative embodiment, the cellulose pulp fibers may
be provided as discrete cellulosic pulp fibers or fiber bundles by
capturing the fibers prior to the typical sheeting and drying
operations. These discrete cellulosic pulp fibers can be
efficiently formed into pellets that are easily handled in
subsequent processes. Pelletizing processes preserve the fiber
length, and hence mechanical properties, to a much greater extent
than granulation processes. Cellulosic fibers exiting a pelletizing
process typically have an average fiber length ranging between
about 0.8 to 2.5 mm. The pelletizing process generally produces
fiber pellets comprised of cellulosic pulp fibers that are
cohesively bound by a suitable amount of at least one water soluble
binder, such as the water soluble polymers described above. The
fiber pellets provide the cellulosic pulp fibers in a form that may
then be readily fed into the compounding extruder and mixed with
the matrix composition during melt blending.
[0050] Pelletization may be accomplished by any means known in the
art. In one advantageous embodiment, a mixer, such as a Hobart
mixer or a pug mill, may be used to initially disperse the water
soluble binder with the cellulosic fibers. A pelletizer, such as a
Kahl pelletizing mill, may then be used to form cylindrical fiber
pellets. Typical fiber pellets range from about 3 to 8 mm in
diameter with a length of about 3 to 9 mm. The fiber pellets
typically have a density of around 0.6 g/cm.sup.3. The fiber
pellets provide improved material handling properties and easier
feeding characteristics for the melt blending operation.
[0051] Advantageously, the dried fiber pellets should have a
moisture content less than about 5% by weight, such as a moisture
content of less than about 1% by weight, and further be
substantially free of solvent. Consequently, the fiber pellets may
beneficially be dried prior to melt blending.
[0052] As shown in FIG. 1, the cellulosic pulp fibers exiting the
fiber preparation step are transported to a melt blending step.
During melt blending, the cellulose pulp fiber pellets are
separated into discrete fibers and are dispersed, or compounded,
within the matrix composition. Melt blending is typically
accomplished by introducing a melt blending composition including
the cellulosic pulp fiber pellets, matrix polymer, and any
additional matrix composition components into a compounding
extruder. Any compounding extruder providing suitably aggressive
mixing, such as a co-rotating twin screw extruder, may be used to
compound the melt blending composition. An exemplary compounding
extruder is schematically illustrated in FIG. 2.
[0053] As indicated in FIG. 2, at least a portion of the melt
blending composition is introduced into a compounding extruder 18
through a main feed throat 20. The melt blending composition
generally includes the cellulosic pulp fiber (advantageously in the
form of fiber pellets containing a suitable binder component), the
matrix polymer, at least one lubricant, and at least one
compatibilizer, as well as the other optional additives described
above. Following its introduction, the melt blending composition is
transported down the length of two co-rotating parallel screws 22,
24, passing through several distinct regions of high temperature
and/or pressure where the polymeric matrix is melted and blended
with the reinforcing fiber and other matrix components prior to
exiting the extruder through a heated die 32. Each of the heated
regions may be formed from one or more temperature controlled
zones. In one advantageous embodiment, the melt blending
composition is transported through at least three heated regions
26, 28, 30 and a heated die 32 during compounding. Upon exiting the
heated die 32, the compounded melt blending composition is quenched
and then chopped or otherwise formed into blended chips which are
suitable to be used in a subsequent molding process.
[0054] In the advantageous embodiment represented in FIG. 2, the
compounding extruder 18 further includes a secondary feed throat 34
for introducing either a secondary portion of one or more
components of the melt blending composition or other additives
downstream of the main feed throat 20. The secondary feed throat 34
may generally be positioned anywhere downstream of the main feed
throat. In the advantageous embodiment depicted in FIG. 2, the
secondary feed throat 34 is positioned about half way between the
main feed throat 20 and the heated die 32.
[0055] Applicants have found that melt blending compositions
incorporating high alpha cellulose pulp fibers may be processed at
extruder setting temperatures below the melting point of the matrix
polymer, as described in U.S. Pat. No. 6,270,883. Applicants have
further determined that a particular skewed parabolic heating
profile may be used in the compounding extender 18 to impart less
discoloration during melt blending without negatively impacting the
resulting fiber dispersion properties. More specifically,
Applicants have determined that melt blending compositions
including cellulosic pulp fibers having an alpha-cellulose purity
of greater than 80% by weight may be beneficially compounded by
passing the melt blending composition sequentially through an
initial region 26 heated to a temperature about 10% below the
matrix polymer melting point, a first intermediate region 28 heated
to a temperature of about 15 to 20 percent below the matrix polymer
melting point, a second intermediate region 30 heated to a
temperature of about 15 to 20 percent above the matrix polymer
melting point, and a die 32 heated to a temperature of about 35 to
40 percent above the matrix polymer melting point.
[0056] The foregoing skewed parabolic heating profile has been
determined to be particularly advantageous in conjunction with
olefinic matrices. For example, in advantageous embodiments
employing polypropylene as the matrix polymer, whose melt
temperature typically ranges between 160 to 165.degree. C., the
initial region 26 may be heated to a temperature ranging between
about 125 to 145.degree. C., the first intermediate region 28 may
be heated to a temperature ranging between about 115 to 135.degree.
C., the second intermediate region 30 may be heated to a
temperature ranging between about 160 to 190.degree. C., and the
die 32 may by heated to a temperature ranging between about 190 to
220.degree. C.
[0057] In beneficial embodiments, compounding can be performed in a
compounding extruder having 12 heated zones, typically of
approximately equal length and diameter, followed by a heated die.
In such beneficial embodiments, the initial heated region 26 may
encompass the first two heated zones, the first intermediate region
28 may encompass the third through eleventh heated zones, and the
second intermediate region 30 may encompass the twelfth heated
zone, as illustrated in FIG. 2.
[0058] The compounding extruder may be of any size and may be
capable of any throughput known in the art for use in melt blending
processes. In one advantageous embodiment, a 40 mm compounding
extruder is employed which is capable of at least about 400
lbs/hour throughput. Extruders suitable for use in the present
invention are commercially available from a number of
manufacturers, including Coperion Corporation.
[0059] Applicants have further determined that the feeding protocol
used to introduce the matrix polymer into the melt blending step
may also impact fiber dispersion properties. More specifically,
Applicants have determined that feeding a first portion of the
matrix polymer through the main feed throat 20 and a second portion
of the matrix polymer through a secondary feed throat 34 positioned
downstream of the main feed throat 20 and upstream of the second
intermediate heated region 30 can result in improved fiber
dispersion within the blended chips.
[0060] For example, to produce blended chips containing
approximately 30% cellulosic pulp fiber, an initial melt blending
composition containing a cellulosic fiber to matrix polymer weight
ratio ranging from about 40:60 to 80:20 may be introduced into the
main feed throat 20 and the remaining matrix polymer required to
dilute the initial melt blending composition down to 30% cellulosic
fiber may be introduced into the secondary feed throat 34. In
alternative aspects of this embodiment, blended chips containing
30% cellulosic pulp fiber may be prepared from initial melt
blending compositions containing from about 40:60 to 70:30
cellulosic fiber to matrix polymer weight ratios, such as initial
melt blending compositions containing from about 45:55 to 60:40
cellulosic fiber to matrix polymer weight ratios. In one
particularly beneficial embodiment, an initial melt blending
composition containing an about 55:45 cellulosic fiber to matrix
polymer weight ratio is employed to make blended chips containing
about 30% cellulosic pulp fiber.
[0061] In additional beneficial aspects, Applicants have determined
that discoloration may be further reduced by feeding a first
portion of the matrix polymer having a fairly low viscosity, e.g. a
comparatively high melt flow index, through the main feed throat 20
of the compounding extruder 18 and a second portion of the matrix
polymer having a higher viscosity, e.g. a comparatively low melt
flow index, through a secondary feed throat 34 positioned
downstream of the main feed throat 20. For example, Applicants have
determined that discoloration may be reduced by feeding a first
portion of the matrix polymer having a melt flow index ranging from
about 30 to 90, such as a melt flow index ranging between about 50
to 80 or about 70 to 80, into the main feed throat 20 of the
compounding extruder 18. A second portion of matrix polymer having
a melt flow index ranging from about 10 to 25, such as a melt flow
index ranging from about 10 to 12, may then be introduced through a
secondary feed throat 34 positioned downstream of the main feed
throat 20 and upstream of a second intermediate heated region, as
shown in FIG. 2. The amount of lower viscosity matrix polymer
introduced into the main feed throat 20, i.e. the first polymer
portion, may generally vary from about 5 to 80 weight percent of
the total amount of the matrix polymer. In further beneficial
aspects of these embodiments, the first polymer portion may
constitute from about 20 to 40 weight percent of the total amount
of the matrix polymer.
[0062] Returning now to FIG. 1, the blended chips exiting the melt
blending process may advantageously be formed into complex three
dimensional articles by molding and the like. Molding compositions
in accordance with the present invention may include the blended
chips alone or in combination with additional amounts of the same
or different matrix polymer. Further, additional additives known in
the molding arts may be included within the molding composition, as
well. As used herein, the term "molding" is meant to encompass any
process in which heat and pressure is applied to the blended chips
to transform them into more complex three dimensional articles.
Exemplary molding operations thus include injection molding,
compression molding, blow molding and rotational molding, as well
as various extrusion and pultrusion processes. Molded articles
formed in accordance may define fairly complex three dimensional
objects, such as objects defining multiple sharp corner radii and
the like. One advantageous embodiment of the present invention
comprises injection molding the blended chips into complex finished
articles, such as molded products employed within the automotive
industry and the like.
[0063] The present invention will be further illustrated by the
following non-limiting examples.
EXAMPLE I
[0064] Fiber Pellet Formation:
[0065] Preparation of Sample 1 Fiber Pellets:
[0066] TERRACEL.TM.-10J fibers in wet fibrous form (water content
between 50 and 60%, based on weight of the wet fibers) were mixed
in a Hobart mixer with sodium carboxymethyl cellulose ("CMC"),
commercially available as Na-CMC-7H4F from Hercules Aqualon
Division. The weight ratio of dry fiber to CMC was 100 to 0.5.
After blending in a Hobart mixer, the cellulose fiber/CMC mixture
was fed to a Kahl pelletizing mill to form cylindrical pellets. The
Kahl Pellet Mill employed was a Type L175 mill, commercially
available from Amandus Kahl Nachf., Hamburg, Germany. The pellet
mill, operating at discharge rates ranging between 0.1 to 0.3
kg/min, produced fiber pellets exhibiting a moisture content of
about 50 to 60%. The fiber pellets were subsequently dried
overnight at 190.degree. F. The fiber pellets generally had a
diameter ranging from about 3 to 8 mm and a length ranging from
about 3 to 9 mm. The fiber pellet density was around 0.6
g/cm.sup.3. After pelletizing, Kajanni fiber length measurements
determined that the WAFL of the fiber pellets was around 1.8
mm.
[0067] Preparation of Sample 2 Fiber Pellets:
[0068] A second set of fiber pellets were prepared by combining
TerraCel.TM. 10J fibers with 0.5 wt % (based on the weight of the
cellulose fiber) polyacrylamide ("PAM") having a molecular weight
of 15.times.10.sup.6 daltons and 1 wt % (based on the weight of the
cellulose fiber) lubricant mixture using the mixing and pelletizing
equipment and conditions described for Sample 1. The PAM was
obtained from Aldrich Chemicals. The lubricant mixture was
comprised of 67 wt % (based on the weight of the lubricant mixture)
SF96-350 silicone oil from GE Silicones and 33 wt. % (based on the
weight of the lubricant mixture) ethylenebisstearamid ("EBS"),
commercially available from Aldrich Chemicals.
[0069] Melt Blending of Sample 1 and 2 Fiber Pellets:
[0070] The fiber pellets identified as Samples 1 and 2 were melt
blended with polypropylene exhibiting a Melt Flow Index ("MFI") of
about 12. The polypropylene employed in Sample 2 was produced by
Basell and obtained via Federal Plastics Corporation, Cranbury,
N.J. A comparable polypropylene was used to form Sample 1. The melt
blending composition further included maleated polypropylene,
commercially available as POLYBOND 3200 from Crompton Corporation,
as a compatibilizer, in an amount of about 2 weight percent, based
on the weight of the melt blending composition. The fiber to
polypropylene weight ratio within the melt blending composition was
30:70.
[0071] The compounding extruder was a 40 mm co-rotating twin-screw
extruder with 12 heated barrel zones and heated die made by
Coperion Corporation, formerly Wemer-Pfleiderer. A throughput rate
of 200 lbs/hour was maintained throughout the melt blending
process. The temperature profile employed during melt blending was:
zones 1-2 at 142.degree. C.; zones 3-11 at 133.degree. C.; zone 12
at 176.degree. C., and die at 210.degree. C.
[0072] The results obtained from the melt blending of Samples 1 and
2 are provided in Table 1 below:
1TABLE 1 Fiber Sample Fiber Pelletization Additives
Yellowness.sup.1 Dispersion.sup.2 1 0.5% CMC 3 Bad 2 0.5% PAM +
1.0% Si Oil/EBS 1 Very Good .sup.1Based on AATCC Gray Scale for
evaluating difference in color, in which a value of 1 indicates
white and a value of 5 indicates a dark tan shade. .sup.2Based on
visual observation of the uniformity of fiber dispersion after
molding the blended chips into a thin film.
[0073] As shown in Table 1, qualitative comparisons between Samples
1 and 2 indicate that a fiber pelletization additive package of
0.5% PAM and 1% Si oil/EBS produced a lighter color and better
dispersion in melt blended chips than 0.5% CMC alone. A visual
inspection of a small amount of blended chip containing 0.5% PAM
without 1.0% Si Oil/EBS similarly indicated that PAM provides
superior color and fiber dispersion results in comparison to CMC,
although sufficient sample was not available for a more detailed
analysis. Further, Sample 2 exhibited superior color and fiber
dispersion characteristics in comparison to PAM alone.
EXAMPLE II
[0074] Preparation of Sample 3:
[0075] Additional fiber pellets based on 0.5% CMC were formed using
the materials and procedures described in Example I for Sample 1.
The fiber pellets were subsequently melt blended with polypropylene
in a 55:45 fiber pellet to matrix polymer weight ratio, using the
polypropylene, equipment, and processing conditions described in
Example I, except that a sufficient amount of polypropylene having
a MFI of about 12 was added to the compounding extruder in a
secondary feed throat downstream of the main feed throat to produce
a final composition within the blended chips produced in Sample 3
of 30% celluose pulp fiber and 70% polypropylene.
[0076] The results obtained from the melt blending of Samples 1
versus 3 are provided in Table 2 below:
2 TABLE 2 Sample Fiber/PP Ratio at Main Feeder Fiber
Dispersion.sup.1 3 55:45 Very Good 1 30:70 Bad .sup.1Based on
visual observation of the uniformity of fiber dispersion after
molding the blended chips into a thin film.
[0077] Fiber ratios higher than 55:45 did not improve the
dispersion anymore. Based on a comparison of Samples 1 and 3, the
use of a fiber to polypropylene weight ratio of about 55:45 at the
main feed throat produced the best dispersion properties.
EXAMPLE III
[0078] Preparation of Sample 4:
[0079] Fiber pellets were formed and subsequently melt blended
using the materials, equipment, and processing conditions described
in Example II for Sample 3, except that the melt flow index of the
polypropylene mixed with the fiber pellets at the main feed throat
ranged from about 70 to 80.
[0080] The results obtained from the melt blending of Samples 3
versus 4 are provided in Table 3 below:
3 TABLE 3 Sample Fiber/PP Ratio at Main Feeder Fiber
Dispersion.sup.1 3 12 Very Good 4 70-80 Excellent .sup.1Based on
visual observation of the uniformity of fiber dispersion after
molding the blended chips into a thin film.
[0081] Based on a comparison of Samples 3 and 4, the use of a
higher MFI, i.e., lower molecular weight PP, in the melt blending
composition supplied to the main feed throat led to a lighter color
and improved fiber dispersion within the resulting blended
chip.
[0082] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *