U.S. patent application number 14/192253 was filed with the patent office on 2014-08-14 for additives for papermaking.
This patent application is currently assigned to NANOPAPER, LLC. The applicant listed for this patent is NANOPAPER, LLC. Invention is credited to Gangadhar Jogikalmath, Andrea Schneider, David S. Soane.
Application Number | 20140224443 14/192253 |
Document ID | / |
Family ID | 47756866 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140224443 |
Kind Code |
A1 |
Jogikalmath; Gangadhar ; et
al. |
August 14, 2014 |
ADDITIVES FOR PAPERMAKING
Abstract
The present invention provides systems and methods for
papermaking. In embodiments, the systems include a first population
of fibers dispersed in an aqueous solution and complexed with an
activator, and a second population of composite additive particles
bearing a tethering material, wherein the addition of the second
population to the first population attaches the composite additive
particles to the fibers by the interaction of the activator and the
tethering material. Methods for forming a fibrous web are also
disclosed, in addition to paper products formed from such fibrous
webs.
Inventors: |
Jogikalmath; Gangadhar;
(Cambridge, MA) ; Schneider; Andrea; (Hyde Park,
MA) ; Soane; David S.; (Chestnut Hill, MA) |
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Applicant: |
Name |
City |
State |
Country |
Type |
NANOPAPER, LLC |
Cambridge |
MA |
US |
|
|
Assignee: |
NANOPAPER, LLC
Cambridge
MA
|
Family ID: |
47756866 |
Appl. No.: |
14/192253 |
Filed: |
February 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US12/53098 |
Aug 30, 2012 |
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14192253 |
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61530260 |
Sep 1, 2011 |
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61660146 |
Jun 15, 2012 |
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Current U.S.
Class: |
162/146 ;
162/141; 162/157.1; 162/158; 162/175; 162/181.2; 162/181.5;
162/181.9 |
Current CPC
Class: |
D21H 17/24 20130101;
D21H 21/10 20130101; D21H 17/28 20130101; D21H 17/67 20130101; D21H
17/33 20130101; D21H 21/18 20130101; D21H 13/00 20130101; D21H
11/00 20130101; D21H 17/675 20130101; D21H 13/12 20130101; D21H
23/04 20130101; D21H 17/29 20130101 |
Class at
Publication: |
162/146 ;
162/158; 162/157.1; 162/181.5; 162/181.9; 162/181.2; 162/175;
162/141 |
International
Class: |
D21H 23/04 20060101
D21H023/04 |
Claims
1. A system for papermaking, comprising: a first population of
fibers dispersed in an aqueous solution and complexed with an
activator, and a second population of composite additive particles
bearing a tethering material, wherein the addition of the second
population to the first population attaches the composite additive
particles to the fibers by the interaction of the activator and the
tethering material.
2. The system of claim 1, wherein the first population comprises
cellulosic fibers.
3. The system of claim 1, wherein the first population comprises
synthetic fibers.
4. The system of claim 1, wherein the composite additive particles
comprise a particle selected from the group of a PCC particle, a
TiO2 particle, a magnetic particle, and a silver colloid
particle.
5. The system of claim 1, wherein the composite additive particles
comprise a latex component and a starch component.
6. A method for manufacturing a paper product, comprising:
activating a first population of fibers in a liquid medium with an
activator, forming a second population of composite additive
particles, treating the second population with a tethering material
to form tether-bearing composite additive particles, wherein the
tethering material is capable of interacting with the activator,
adding the second population to the activated population of fibers
to form a treated paper matrix, and forming the paper matrix to
manufacture the paper product.
7. The method of claim 6, wherein the first population comprises
cellulosic fibers.
8. The method of claim 6, wherein the first population comprises
synthetic fibers.
9. The method of claim 6, wherein the composite additive particles
comprise a particle selected from the group of a PCC particle, a
TiO2 particle, a magnetic particle, and a silver colloid
particle.
10. The method of claim 6, wherein the composite additive particles
comprise a latex component and a starch component.
11. A method of manufacturing a paper product, comprising:
providing a first population of fibers and a second population of
fibers, wherein the fibers have low attachable affinity for each
other, activating the first population of fibers in a liquid medium
with an activator, treating the second population of fibers with a
tethering material to form tether-bearing fibers, wherein the
tethering material is capable of interacting with the activator,
adding the second population of tether-bearing fibers to the
activated population of fibers to form a treated paper matrix, and
forming the paper matrix to manufacture the paper product.
12. The method of claim 11, wherein at least one population of
fibers comprises synthetic fibers.
13. The method of claim 12, wherein at least one population of
fibers comprises cellulosic fibers.
14. The method of claim 11, wherein one of the first population and
the second population comprises hardwood fibers, and the other of
the first population and the second population comprises softwood
fibers.
15. A fibrous web, comprising: a first population of fibers and a
second population of fibers, wherein an activator has been attached
to the first population of fibers and a tethering material has been
attached to the second population of fibers, the tethering material
interacting with the activator to attach the first population of
fibers to the second population of fibers as a fibrous web.
16. A paper product, comprising the fibrous web of claim 15.
17. The paper product of claim 16, wherein the first population of
fibers comprises cellulosic fibers, and the second population of
fibers comprises synthetic fibers.
18. The paper product of claim 17, wherein the first population of
fibers consists essentially of cellulosic fibers, and the second
population of fibers consists essentially of synthetic fibers.
19. The paper product of claim 17, wherein the first population of
fibers comprises one of softwood fibers or hardwood fibers, and the
second population of fibers comprises the other of softwood and
hardwood fibers.
20. The paper product of claim 17, wherein the first population of
fibers comprises cellulosic fibers, and the second population of
fibers comprises non-cellulosic natural fibers.
21. A method of forming a fibrous web, comprising: providing a
first population of fibers, activating the first population of
fibers in a liquid medium with an activator, preparing a population
of composite particles, wherein the composite particles comprise a
latex component and a starch component, treating the population of
composite particles with a tethering material to form
tether-bearing composite particles, wherein the tethering material
is capable of interacting with the activator to attach the
composite particles to the fibers to form particle-bearing fibers,
and processing the particle-bearing fibers to gelatinize the starch
component and to melt the latex component, thereby distributing the
melted latex component through the fibers and binding the fibers
together to form the fibrous web.
22. The method of claim 20, further comprising: providing a second
population of fibers, wherein the second population of fibers has
low attachable affinity for the first population, activating the
second population of fibers with an activator, and adding the
second population of fibers to the first population of fibers
either before or after the activation step for either population,
wherein the population of tether-bearing composite particles
attaches to the first population of fibers and the second
population of fibers to form particle-bearing fibers, and wherein
the processing of the particle-bearing fibers distributes the
melted latex component through the first population and the second
population of fibers and binds the first population and the second
population of fibers together to form the fibrous web.
23. A paper product formed from the fibrous web of claim 20.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/US12/53098, which designated the United States
and was filed on Aug. 30, 2012, published in English, which claims
the benefit of U.S. Provisional Application Ser. No. 61/530,260,
filed Sep. 1, 2011 and U.S. Provisional Application Ser. No.
61/660,146, filed Jun. 15, 2012. The entire contents of the above
applications are incorporated by reference herein.
FIELD OF THE APPLICATION
[0002] This application relates generally to making high-strength
paper products with specific functionalities.
BACKGROUND
[0003] Many paper applications require not only high strength but
also functionalities that provide the paper article with moisture,
oil and grease, mold and fire resistance, increased brightness, or
other specialized functionalities like antimicrobial properties or
magnetic properties. Certain of these products are currently
manufactured by imparting paper a coating in a secondary
process.
[0004] In one approach for adding functionality to the paper
surface, the sizing process uses cooked starch solutions with
additives (such as brightening agents, clays, hydrophobicizing
compounds) to impart surface functionality to the paper. In the
sizing process, the wet web is first dried to a pre-set moisture
content and/or is re-wet to achieve uniform moisture content
throughout; then the material is fed into a size press where a high
loading of gelatinized starch with additives is applied to the
paper surface; then the material is dried again. This process
involves a number of downstream processes that can be inefficient.
Inefficiencies result from the number of steps involved in
preparing the substrate, cooking the starch and applying it to form
the finished product. A considerable amount of energy is required
for these steps, which adds to the costs of the process.
[0005] For certain paper products, functionalities can be added by
incorporating additives into the fibrous matrix during the
papermaking process. Particulate additives can be introduced into
the paper web, substituting for some of the pulp that might be used
otherwise. These particulate fillers can create, for example, a
bulky final paper product that creates the impression of higher
quality through its tactile properties while minimizing the use of
expensive pulp. Particulate fillers can also be used to impart
other specialized properties besides bulk. For example, particulate
additives can include filler particles, or other particles,
suitable for use in papermaking, or a final paper product can
include mineral particles such as calcium carbonate, dolomite,
calcium sulfate, kaolin, talc, titanium dioxide, silica, aluminum
hydroxide, and the like. Particles can be formed from inorganic or
organic materials, and may be solid or porous. Organic particles
may be polymeric, optionally crosslinked, and may be elastomeric. A
wide variety of particles known in the art can be incorporated into
the finished paper product to improve performance attributes such
as brightness, opacity, smoothness, ink receptivity, fire
retardance, water resistance, bulk, and the like.
[0006] Precipitated Calcium Carbonate (PCC) is particularly useful
as a particulate filler additive where high opacity, brightness and
maintenance of caliper are required. Higher PCC contents replace
expensive pulp improving the profitability of paper. Although PCC
contents as high as 15% are often used in papermaking, the first
pass retention of the filler is poor, so that a significant amount
can be lost from the paper product during the papermaking process.
The PCC that is incorporated into the paper product also leads to
weaker sheets, because the particles themselves disrupt the
hydrogen bonding between cellulose fibers. Higher ash content
(>15%) is highly desired in the paper industry, where ash
content indicates the amount of filler in a paper.
[0007] In other products, TiO2 particles are highly desired as
particulate fillers to improve the opacity and brightness beyond
what is achievable using PCC. The TiO2 particles due to their small
size and high refractive index are capable of scattering light and
improving the opacity of the paper containing them. As the TiO2
particles are many times more expensive than PCC, improvement in
retention is highly desired. Although flocculants can be used to
improve the retention of TiO2, the flocculated TiO2 particles do
not possess the same optical properties as the individual TiO2
platelets. It would be advantageous to combine TiO2 particles with
other particles to form a composite that separates individual TiO2
particles and allows them to retain their optical
characteristics.
[0008] Other particulate fillers can be added to the paper product
to impart specific, desirable properties. As an example, magnetic
or paramagnetic particles can be incorporated into the paper to
form a magnetic or a magnetizable paper. As another example,
colloidal silver particles can be introduced into a paper product
to impart antimicrobial properties. A large number of additives can
be contemplated that are available in particulate form, including
additives that impart oil or grease resistance, optical
brightening, ink binding, dust control, water repellency,
stiffness, biocidal properties, bioactive properties (e.g., a
biomolecule for controlled release), adhesive properties,
diagnostic sensing, filtration assist, targeted
capture/sequestration, and the like. For particulate additives,
proper distribution within the paper matrix is important. For
particulate additives that are expensive, proper retention is also
important. And with the addition of any additive, its impact on the
strength, stiffness and bulk of the final paper product must be
considered.
[0009] A variety of other additives can be used to impart desirable
properties to paper products, but face some of the same challenges:
retention, distribution and impact on paper quality. Some other
additives used presently to impart various functionalities to paper
include synthetic fibers (imparting strength and hydrophobicity and
absorbency characteristics), latex colloids (imparting properties
such as hydrophobicity, oil and grease resistance, mold resistance,
fire retardancy, impact resistance) etc. These components have poor
affinity to pulp fibers, though, owing to lack of functional groups
capable of interacting with cellulose fibers. As an example, latex
colloids are particularly useful for imparting resilience, barrier
properties, bulk, impact resistance, damping, and the like. Latex
particles that are micron or submicron sized (typically 100 nm
particles) suspended in an aqueous solution are particularly suited
for use in papermaking. However, latex is typically
water-insoluble, and can be integrated only with great difficulty
into an aqueous process like papermaking.
[0010] It is desirable, therefore, to have a process where an
additive capable of delivering added functionality can be mixed
with pulp fibers in the wet-end of papermaking such that the
additive becomes an integral part of it. It is desirable that such
additives be distributed evenly and appropriately within the paper
matrix, and that the additives be retained on the product and not
lost in the whitewater. It is further desirable to introduce such
additives so that they preserve the strength and resiliency of the
final paper product.
[0011] As an example, there exists a particular need in the art for
systems and methods that incorporate and retain colloidal latex
particles in the wet end so that high amounts of these fillers are
dispersed uniformly in the paper providing paper with desired
functionalities. These colloidal latex fillers should, desirably,
be incorporated so that they are stably anchored to the pulp
fibers, allowing them to expand or gelatinize during paper
manufacturing without being dislodged. In this manner, the fillers
can occupy the interstitial spaces between cellulose fibers more
completely, improving the properties of the paper product.
Furthermore, it is known that high filler content has a detrimental
effect on the strength of the wet web before it is dried because
the fillers act as spacers and interfere with fiber-fiber bonding.
An efficient retention system that attaches the latex fillers to
fibers durably in the wet web can advantageously enhance wet web
strength during processing by allowing fiber-fiber bonding to
proceed unimpeded.
SUMMARY
[0012] Disclosed herein in embodiments are systems for papermaking,
comprising a first population of fibers dispersed in an aqueous
solution and complexed with an activator, and a second population
of composite additive particles bearing a tethering material,
wherein the addition of the second population to the first
population attaches the composite additive particles to the fibers
by the interaction of the activator and the tethering material. The
first population can comprise cellulosic or synthetic fibers. The
composite additive particles can comprise a particle selected from
the group of a PCC particle, a TiO2 particle, a magnetic particle,
and a silver colloid particle. In embodiments, the composite
additive particles comprise a latex component and a starch
component.
[0013] Further disclosed herein, in embodiments, are methods for
manufacturing a paper product, comprising activating a first
population of fibers in a liquid medium with an activator, forming
a second population of composite additive particles, treating the
second population with a tethering material to form tether-bearing
composite additive particles, wherein the tethering material is
capable of interacting with the activator, adding the second
population to the activated population of fibers to form a treated
paper matrix, and forming the paper matrix to manufacture the paper
product. In embodiments, the first population comprises cellulosic
fibers or synthetic fibers. In embodiments, the composite additive
particles comprise a particle selected from the group of a PCC
particle, a TiO2 particle, a magnetic particle, and a silver
colloid particle. In embodiments, the composite additive particles
comprise a latex component and a starch component.
[0014] Also disclosed herein, in embodiments, are methods for
making a paper product, comprising providing a first population of
fibers and a second population of fibers, wherein the fibers have
low attachable affinity for each other, activating the first
population of fibers in a liquid medium with an activator, treating
the second population of fibers with a tethering material to form
tether-bearing fibers, wherein the tethering material is capable of
interacting with the activator, adding the second population of
tether-bearing fibers to the activated population of fibers to form
a treated paper matrix, and forming the paper matrix to manufacture
the paper product. In embodiments, at least one population of
fibers comprises synthetic or cellulosic fibers. In embodiments,
one of the first population and the second population comprises
hardwood fibers, and the other of the first population and the
second population comprises softwood fibers.
[0015] Also disclosed, in embodiments, is a fibrous web, comprising
a first population of fibers and a second population of fibers,
wherein an activator has been attached to the first population of
fibers and a tethering material has been attached to the second
population of fibers, the tethering material interacting with the
activator to attach the first population of fibers to the second
population of fibers as a fibrous web. Also disclosed, in
embodiments, is a paper product comprising the fibrous web as
described above. In embodiments, the first population of fibers in
the fibrous web comprises cellulosic fibers, and the second
population of fibers comprises synthetic fibers. In embodiments,
the first population of fibers consists essentially of cellulosic
fibers, and the second population of fibers consists essentially of
synthetic fibers. In embodiments, the first population of fibers
comprises one of softwood fibers or hardwood fibers, and the second
population of fibers comprises the other of softwood and hardwood
fibers. In embodiments, the first population of fibers comprises
cellulosic fibers, and the second population of fibers comprises
non-cellulosic natural fibers. In embodiments, the first population
of fibers comprises one of softwood fibers or hardwood fibers, and
the second population of fibers comprises the other of softwood and
hardwood fibers.
[0016] In addition, disclosed herein in embodiments are methods of
forming a fibrous web, comprising providing a first population of
fibers, activating the first population of fibers in a liquid
medium with an activator, preparing a population of composite
particles, wherein the composite particles comprise a latex
component and a starch component, treating the population of
composite particles with a tethering material to form
tether-bearing composite particles, wherein the tethering material
is capable of interacting with the activator to attach the
composite particles to the fibers to form particle-bearing fibers,
and processing the particle-bearing fibers to gelatinize the starch
component and to melt the latex component, thereby distributing the
melted latex component through the fibers and binding the fibers
together to form the fibrous web. The method can further comprise
the steps of providing a second population of fibers, wherein the
second population of fibers has low attachable affinity for the
first population, activating the second population of fibers with
an activator, and adding the second population of fibers to the
first population of fibers either before or after the activation
step for either population, wherein the population of
tether-bearing composite particles attaches to the first population
of fibers and the second population of fibers to form
particle-bearing fibers, and wherein the processing of the
particle-bearing fibers distributes the melted latex component
through the first population and the second population of fibers
and binds the first population and the second population of fibers
together to form the fibrous web. In embodiments, paper products
formed from the fibrous web described above are also disclosed.
BRIEF DESCRIPTION OF THE FIGURES
[0017] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0018] FIG. 1 shows a photograph of samples of latex and cationic
starch in water.
[0019] FIG. 2 shows a graph of normalized load for pulp controls
vs. experimental preparations.
[0020] FIG. 3 shows a table indicating hydrophobicity for various
samples.
[0021] FIG. 4 shows a graph of normalized load for pulp controls
vs. experimental preparations.
[0022] FIG. 5 shows a table indicating hydrophobicity for various
samples.
[0023] FIG. 6 shows a graph of normalized load for pulp controls
vs. experimental preparations.
[0024] FIG. 7 shows a table indicating hydrophobicity for various
samples.
[0025] FIG. 8 shows a graph of normalized load for pulp plus
additive controls vs. experimental preparations.
DETAILED DESCRIPTION
[0026] 1. Additives for Papermaking
[0027] Disclosed herein are systems and methods for attaching
additives to cellulose fibers in a paper product. As used herein,
the terms "paper" and "paper product" may be applied to a wide
variety of sheet-like masses, molded products, and other substrates
fabricated from fibers derived from biological sources (e.g.,
fibrous cellulosic material), which may optionally include other
fibrous elements derived from mineral sources (e.g., asbestos or
glass) and/or from synthetic sources (e.g., polyamides, polyesters,
rayon and polyacrylic resins). As disclosed herein, a variety of
specialized additives can be attached to the fibers in the paper
product.
[0028] In embodiments, the additives are combined to form composite
particles, and the composite particles are attached to the
cellulose fibers. Composite particles can be formed by attaching
two or more additives to each other; the composite particles can
then be attached to the cellulose fibers. Three steps can be
performed to effect the attachment of composite particle to
cellulose fibers. In one step, the cellulose fibers are modified by
the attachment of an agent, called an "activating agent" or
"activator" that prepares the surface of the fibers for attachment
to a suitably-modified composite particle. In another step, the
composite particle is formed as will be described in more detail
below. The composite particle is then modified by attaching a
tethering agent to the particle, where the tethering agent has a
particular affinity for the activating agent attached to the paper
fibers. The tether-bearing composite additive particles are then
admixed with the activated fibers, so that the activating agent and
the tethering agents interact: this interaction durably affixes the
composite additive particles bearing the tethers to the fibers
bearing the activators. In embodiments, the cellulose fibers can be
treated with a cationic polymer of a specific molecular weight and
composition as an activator, and the composite additive particles
are treated with an anionic polymer as a tethering agent; these
separately-treated populations are then combined so that the
composite additive particles are attached to the pulp fibers. In
embodiments, the combination of these processes can be referred to
as an "Anchor-Tether-Activator," or "ATA" system. In this system,
the cellulose fibers are treated with the activator, as will be
described below in more detail; the composite additive particle
acts as an "anchor particle" that is treated with the tethering
agent. The tether-bearing anchor particles, when mixed with the
activated cellulose fibers, become attached thereto, so that the
composite additive particles become durably affixed to the
cellulose and appropriately distributed throughout the cellulose
matrix.
[0029] In embodiments, the tethering agent also acts to attach the
component additives to each other to form a composite additive
particle. This use of the tethering agent can allow the creation of
composite particles from components that have no intrinsic
attraction to each other. For example, PCC and TiO2 can be combined
to form a composite additive particle using the tethering agent as
"glue" to hold the components together as a composite. Or, for
example, TiO2 can be combined with another additive, such as clay,
to form a composite additive particle, using the tether as a "glue"
to hold the composite together. The composite additive particle,
thus treated with the tethering agent, forms a tether-bearing
composite particle that is affixable to the activator-treated
cellulose fibers in the anchor-tether-activator system as described
herein.
[0030] In embodiments, the components of the composite additive
particle can be attached to each other intrinsically. In one
embodiment, for example, starch granules and PCC particles can be
mixed together physically to form a composite particle slurry. PCC
is slightly cationic at the pH used for papermaking, which makes it
easier to bond with anionic starch granules. With neutral or
uncharged starch granules, PCC can be mixed at high shear to form a
composite additive particle slurry that can then be modified with
tethering agent.
[0031] As another example, colloidal latex particles can interact
electrostatically with granular starch of opposite charge resulting
in a composite latex/starch additive particle. The composite
latex-starch additive particle can then be treated with a tethering
agent as described herein, and affixed to the activated cellulose
fibers. When prepared and deployed in accordance with these systems
and methods, such a composite latex/starch additive can then used
as functional additive with appropriate chemistry to improve
bonding and retention in the pulp in the wet-end of papermaking. In
embodiments, the granular starch particles can be used to deliver
the latex into the papermaking web so that they are distributed
throughout the fibrous matrix. Attached to the starch granules by
electrostatic attraction, the latex particles then become embedded
uniformly in the fibrous web. As the starch granules gelatinize
during the papermaking process, they further spread the attached
latex particles throughout the paper and onto the surface of the
paper. These latex particles, depending on their melting or
softening point, may then be advantageously incorporated in the
final paper product, for example, forming a film in the paper
during the paper drying process or otherwise imparting desirable
latex properties to the final paper product. In embodiments, starch
granules encrusted with latex (i.e., the composite latex/starch
additive) helps to distribute the latex throughout the fibrous
sheet via gelatinization and film formation.
[0032] In embodiments, latex polymers are selected that are
oppositely charged from the starch granule that is selected to form
the composite. Thus, latex/starch composites are formed and
stabilized by electrostatic forces. As used herein, the term
"latex" refers to a lyophobic colloidal suspension of a synthetic
polymer or a natural polymer (such as hydrocolloid particles of
gums, methyl cellulose, CMC, and the like) in a liquid phase. The
terms "latex polymer" or "latex particle" refer to the polymeric
material suspended in such a colloidal suspension. Latex comprising
synthetic polymers can be produced by a polymerization reaction ex
vivo. Examples of synthetic latex polymers or particles include
styrene-butadiene rubber, acrylonitrile butadiene styrene, acrylic
polymers, polyvinyl acetate polymers, and the like.
[0033] For the uses as disclosed herein, a suitable latex can be
chosen from a wide variety of polymers. Some species of latex are
inert polymers (Polyvinylacetate) while some are reactive (acrylic
based), capable of flowing and crosslinking in the high temperature
encountered in the drying section of papermaking Latex can also be
selected according to the properties of its component polymers. For
example, a useful latex can be comprised of glassy polymers such as
polystyrene when stiffness is required, or rubbery polymers such as
styrene-butadiene copolymers, when flexibility is required. In
embodiments, a cationic latex is used that can be combined with a
negatively charged starch particle.
[0034] Composite starch-latex additive particles as described
herein can then be attached to the fibrous matrix formed by the
papermaking process. The composite starch-latex particles, however,
lack strong affinity to the natural and/or synthetic fibers used to
form the paper web. Hence, additional steps as disclosed herein can
be performed to attach the composite starch-latex particles to the
fibrous web.
[0035] In embodiments, three steps as described previously can be
performed to effect this attachment. In one step, the fibers are
modified by the attachment of an agent, called an "activating
agent," that prepares the surface of the fibers for attachment to a
suitably-modified composite starch-latex particle. In another step,
the starch-latex particle is modified by attaching a tethering
agent to the particle, where the tethering agent has a particular
affinity for the activating agent attached to the paper fibers. The
tether-bearing starch-latex particles are then admixed with the
activated fibers, so that the activating agent and the tethering
agents interact: this interaction durably affixes the composite
particles bearing the tethers to the fibers bearing the activators.
In embodiments, these systems and methods can be used to treat
fibers used in papermaking with a cationic polymer of a specific
molecular weight and composition as an activator, to treat
composite starch-latex granules with an anionic polymer as a
tethering agent, and to combine these separately treated
populations so that the starch granules are attached to the pulp
fibers.
[0036] The present disclosure from time to time refers to fibers
used in papermaking as "pulp fibers." It is recognized, though,
that a variety of fibers can be used in papermaking. As used
herein, the term "fiber" can include natural fibers or synthetic
fibers. Natural fibers can include fibers from animal sources
(e.g., wool, hair, silk), fibers from plant sources (e.g., cotton,
flax, jute, cellulose), and fibers from mineral sources (e.g.,
asbestos, glass). As used herein, the term "natural fiber" refers
to a fiber or a microfiber derived from a natural source without
artificial modification. Natural fibers include vegetable-derived
fibers, animal-derived fibers and mineral-derived fibers.
Vegetable-derived fibers can be predominately cellulosic, e.g.,
cotton, jute, flax, hemp, sisal, ramie, and the like.
Vegetable-derived fibers can include fibers derived from seeds or
seed cases, such as cotton or kapok. Vegetable-derived fibers can
include fibers derived from leaves, such as sisal and agave.
Vegetable-derived fibers can include fibers derived from the skin
or bast surrounding the stem of a plant, such as flax, jute, kenaf,
hemp, ramie, rattan, soybean fibers, vine fibers, jute, kenaf,
industrial hemp, ramie, rattan, soybean fiber, and banana fibers.
Vegetable-derived fibers can include fibers derived from the fruit
of a plant, such as coconut fibers. Vegetable-derived fibers can
include fibers derived from the stalk of a plant, such as wheat,
rice, barley, bamboo, and grass. Vegetable-derived fibers can
include wood fibers. Animal-derived fibers typically comprise
proteins, e.g., wool, silk, mohair, and the like. Animal-derived
fibers can be derived from animal hair, e.g., sheep's wool, goat
hair, alpaca hair, horse hair, etc. Animal-derived fibers can be
derived from animal body parts, e.g., catgut, sinew, etc.
Animal-derived fibers can be collected from the dried saliva or
other excretions of insects or their cocoons, e.g., silk obtained
from silkworm cocoons. Animal-derived fibers can be derived from
feathers of birds. Mineral-derived natural fibers are obtained from
minerals. Mineral-derived fibers can be derived from asbestos.
Mineral-derived fibers can be a glass or ceramic fiber, e.g., glass
wool fibers, quartz fibers, aluminum oxide, silicon carbide, boron
carbide, and the like.
[0037] Synthetic fibers are fibers that are manufactured in whole
or in part. Synthetic fibers include artificial fibers, where a
natural precursor fiber is modified to form a fiber. Cellulose can
also be modified to produce cellulose acetate fibers, and can form
artificial fibers such as Rayon or Lyocell. In embodiments,
artificial fibers can include fibers made from cellulose
substrates, for example cellulose esters (e.g., cellulose acetate),
rayon, bamboo fiber, lyocells, viscose rayon, and the like.
Synthetic fibers also include fibers made from non-natural sources,
can include fibers made from polyesters, aramids, acrylics, nylons,
polyurethane, polyolefin, polyactides, and the like. Synthetic
fibers can be formed from synthetic materials that are inorganic or
organic.
[0038] 2. The Attachment Process
[0039] a. Activation
[0040] As used herein, the term "activation" refers to the
interaction of an activating material, such as a polymer, with
suspended particles or fibers in a liquid medium, such as an
aqueous solution. An "activator," for example an "activator
polymer," can carry out this activation. In embodiments, high
molecular weight polymers can be introduced into the particulate or
fibrous dispersion as activator polymers, so that these polymers
interact, or complex, with the dispersed particles or fibers. The
polymer-fiber complexes interact with other similar complexes, or
with other fibers, and form agglomerates.
[0041] This "activation" step can function as a pretreatment to
prepare the surface of the suspended material (e.g., fibers) for
further interactions in the subsequent phases of the disclosed
system and methods. For example, the activation step can prepare
the surface of the suspended materials to interact with other
polymers that have been rationally designed to interact therewith
in a subsequent "tethering" step, as described below. Not to be
bound by theory, it is believed that when the suspended materials
(e.g., fibers) are coated by an activating material such as a
polymer, these coated materials can adopt some of the surface
properties of the polymer or other coating. This altered surface
character in itself can be advantageous for retention, attachment
and/or dewatering.
[0042] In another embodiment, activation can be accomplished by
chemical modification of the suspended material. For example,
oxidants or bases/alkalis can increase the negative surface energy
of fibers or particles, and acids can decrease the negative surface
energy or even induce a positive surface energy on suspended
material. In another embodiment, electrochemical oxidation or
reduction processes can be used to affect the surface charge on the
suspended materials. These chemical modifications can produce
activated particulates that have a higher affinity for tethered
anchor particles as described below.
[0043] Suspended materials suitable for modification, or
activation, can include organic or inorganic particles, or mixtures
thereof. Inorganic particles can include one or more materials such
as calcium carbonate, dolomite, calcium sulfate, kaolin, talc,
titanium dioxide, sand, diatomaceous earth, aluminum hydroxide,
silica, other metal oxides and the like.
[0044] Organic particles can include one or more materials such as
starch, modified starch, polymeric spheres (both solid and hollow),
carbon based nanoparticles such as carbon nanotubes and the like.
Particle sizes can range from a few nanometers to few hundred
microns. In certain embodiments, macroscopic particles in the
millimeter range may be suitable.
[0045] In embodiments, suspended materials may comprise materials
such as lignocellulosic material, cellulosic material, minerals,
vitreous material, cementitious material, carbonaceous material,
plastics, elastomeric materials, and the like. In embodiments,
cellulosic and lignocellulosic materials may include wood materials
such as wood flakes, wood fibers, wood waste material, wood powder,
lignins, wood pulp, or fibers from woody plants.
[0046] The "activation" step may be performed using flocculants or
other polymeric substances. Preferably, the polymers or flocculants
can be charged, including anionic or cationic polymers.
[0047] In embodiments, anionic polymers can be used, including, for
example, olefinic polymers, such as polymers made from
polyacrylate, polymethacrylate, partially hydrolyzed
polyacrylamide, and salts, esters and copolymers thereof such as
(sodium acrylate/acrylamide) copolymers, sulfonated polymers, such
as sulfonated polystyrene, and salts, esters and copolymers
thereof. Suitable polycations include: polyvinylamines,
polyallylamines, polydiallyldimethylammoniums (e.g., the chloride
salt), branched or linear polyethyleneimine, crosslinked amines
(including epichlorohydrin/dimethylamine, and
epichlorohydrin/alkylenediamines), quaternary ammonium substituted
polymers, such as (acrylamide/dimethylaminoethylacrylate methyl
chloride quat) copolymers and
trimethylammoniummethylene-substituted polystyrene, and the like.
Nonionic polymers suitable for hydrogen bonding interactions can
include polyethylene oxide, polypropylene oxide,
polyhydroxyethylacrylate, polyhydroxyethylmethacrylate, and the
like. In embodiments, an activator such as polyethylene oxide can
be used as an activator with a cationic tethering material in
accordance with the description of tethering materials below. In
embodiments, activator polymers with hydrophobic modifications can
be used. Flocculants such as those sold under the trademark
MAGNAFLOC.RTM. by Ciba Specialty Chemicals can be used.
[0048] In embodiments, activators such as polymers or copolymers
containing carboxylate, sulfonate, phosphonate, or hydroxamate
groups can be used. These groups can be incorporated in the polymer
as manufactured, alternatively they can be produced by
neutralization of the corresponding acid groups, or generated by
hydrolysis of a precursor such as an ester, amide, anhydride, or
nitrile group. The neutralization or hydrolysis step could be done
on site prior to the point of use, or it could occur in situ in the
process stream.
[0049] The activated suspended material (e.g., fiber) can also be
an amine functionalized or modified. As used herein, the term
"modified material" can include any material that has been modified
by the attachment of one or more amine functional groups as
described herein. The functional group on the surface of the
suspended material can be from modification using a multifunctional
coupling agent or a polymer. The multifunctional coupling agent can
be an amino silane coupling agent as an example. These molecules
can bond to a material's surface and then present their amine group
for interaction with the particulate matter. In the case of a
polymer, the polymer on the surface of a suspended fiber or
particle can be covalently bound to the surface or interact with
the surface of the particle and/or fiber using any number of other
forces such as electrostatic, hydrophobic, or hydrogen bonding
interactions. In the case that the polymer is covalently bound to
the surface, a multifunctional coupling agent can be used such as a
silane coupling agent. Suitable coupling agents include isocyano
silanes and epoxy silanes as examples. A polyamine can then react
with an isocyano silane or epoxy silane for example. Polyamines
include polyallyl amine, polyvinyl amine, chitosan, and
polyethylenimine.
[0050] In embodiments, polyamines (polymers containing primary,
secondary, tertiary, and/or quaternary amines) can also
self-assemble onto the surface of the suspended particles or fibers
to functionalize them without the need of a coupling agent. For
example, polyamines can self-assemble onto the surface of the
particles or fibers through electrostatic interactions. They can
also be precipitated onto the surface in the case of chitosan for
example. Since chitosan is soluble in acidic aqueous conditions, it
can be precipitated onto the surface of suspended material by
adding a chitosan solution to the suspended material at a low pH
and then raising the solution pH.
[0051] In embodiments, the amines or a majority of amines are
charged. Some polyamines, such as quarternary amines are fully
charged regardless of the pH. Other amines can be charged or
uncharged depending on the environment. The polyamines can be
charged after addition onto the suspended particles or fibers by
treating them with an acid solution to protonate the amines. In
embodiments, the acid solution can be non-aqueous to prevent the
polyamine from going back into solution in the case where it is not
covalently attached to the particle or fiber.
[0052] The polymers or particles can complex via forming one or
more ionic bonds, covalent bonds, hydrogen bonding and combinations
thereof, for example. Ionic complexing is preferred.
[0053] To obtain activated suspended materials, the activator could
be introduced into a liquid medium through several different means.
For example, a large mixing tank could be used to mix an activating
material with fine particulate materials. Activated particles or
fibers are produced that can be treated with one or more subsequent
steps of attachment to tether-bearing anchor particles.
[0054] b. Tethering
[0055] As used herein, the term "tethering" refers to an
interaction between an activated suspended particle or fiber and an
additive particle, herein termed an anchor particle (as described
below). The additive particle, for example, a composite additive
particle, ("anchor particle") can be treated or coated with a
tethering material. The tethering material, such as a polymer,
forms a complex or coating on the surface of the anchor particles
such that the tethered anchor particles have an affinity for the
activated suspended material. In embodiments, the selection of
tether and activator materials is intended to make the two solids
streams complementary so that the activated particles or fibers in
the suspension become tethered, linked or otherwise attached to the
anchor particle.
[0056] In accordance with these systems and methods, the tethering
material acts as a complexing agent to affix the activated
particles or fibers to the additive particle anchor material. In
embodiments, a tethering material can be any type of material that
interacts strongly with the activating material and that is
connectable to an anchor particle. Composite latex-starch particles
are an example of an additive particle or anchor particle that can
be treated with a tethering agent.
[0057] In embodiments, various interactions such as electrostatic,
hydrogen bonding or hydrophobic behavior can be used to affix an
activated complex to a tethering material complexed with an anchor
particle.
[0058] For use in papermaking, an anchor particle can be selected
from any particulate matter that is desirably attached to cellulose
fibers in the final paper product. The tether-bearing anchor
particle comprising the desirable additive can then interact with
the activated cellulose fibers in the wet paper stream. As an
example, starch granules can be used as an anchor particle to be
attached to the cellulose fibers, as is described in more detail
below. Or, as described herein, composite latex-starch granules can
be used as anchor particles, to be attached via tethering agents to
activated fibers.
[0059] In embodiments, polymers such as linear or branched
polyethyleneimine can be used as tethering materials. It would be
understood that other anionic or cationic polymers could be used as
tethering agents, for example polydiallyldimethylammonium chloride
(poly(DADMAC)). In other embodiments, cationic tethering agents
such as epichlorohydrin dimethylamine (epi/DMA), styrene maleic
anhydride imide (SMAI), polyethylene imide (PEI), polyvinylamine,
polyallylamine, amine-aldehyde condensates, poly(dimethylaminoethyl
acrylate methyl chloride quaternary) polymers and the like can be
used. Advantageously, cationic polymers useful as tethering agents
can include quaternary ammonium or phosphonium groups.
Advantageously, polymers with quaternary ammonium groups such as
poly(DADMAC) or epi/DMA can be used as tethering agents. In other
embodiments, polyvalent metal salts (e.g., calcium, magnesium,
aluminum, iron salts, and the like) can be used as tethering
agents. In other embodiments cationic surfactants such as
dimethyldialkyl(C8-C22)ammonium halides,
alkyl(C8-C22)trimethylammonium halides,
alkyl(C8-C22)dimethylbenzylammonium halides, cetyl pyridinium
chloride, fatty amines, protonated or quaternized fatty amines,
fatty amides and alkyl phosphonium compounds can be used as
tethering agents. In embodiments, polymers having hydrophobic
modifications can be used as tethering agents.
[0060] The efficacy of a tethering material, however, can depend on
the activating material. A high affinity between the tethering
material and the activating material can lead to a strong and/or
rapid interaction there between. A suitable choice for tether
material is one that can remain bound to the anchor surface, but
can impart surface properties that are beneficial to a strong
complex formation with the activator polymer. For example, a
polyanionic activator can be matched with a polycationic tether
material or a polycationic activator can be matched with a
polyanionic tether material. In one embodiment, a poly(sodium
acrylate-co-acrylamide) activator is matched with a chitosan tether
material.
[0061] In hydrogen bonding terms, a hydrogen bond donor should be
used in conjunction with a hydrogen bond acceptor. In embodiments,
the tether material can be complementary to the chosen activator,
and both materials can possess a strong affinity to their
respective deposition surfaces while retaining this surface
property.
[0062] In other embodiments, cationic-anionic interactions can be
arranged between activated suspended materials and tether-bearing
anchor particles. The activator may be a cationic or an anionic
material, as long as it has an affinity for the suspended material
to which it attaches. The complementary tethering material can be
selected to have affinity for the specific anchor particles being
used in the system. In other embodiments, hydrophobic interactions
can be employed in the activation-tethering system.
[0063] 3. Retention and Incorporation in Papermaking
[0064] It is envisioned that the complexes formed from the additive
or composite additive ("anchor") particles and the activated
fibrous matter can form a homogeneous part of a fibrous product
like paper. In embodiments, the interactions between the activated
suspended fibers and the tether-bearing anchor particles can
enhance the mechanical properties of the complex that they form.
For example, an activated suspended material can be durably bound
to one or more tether-bearing anchor particles, so that the
tether-bearing anchor particles do not segregate or move from their
position on the fibers. Increased compatibility of the activated
fine materials with a denser (anchor) matrix modified with the
appropriate tether polymer can lead to further mechanical stability
of the resulting composite material. For example, using
latex-starch composites as tether-bearing anchor particles permits
the latex to attach durably to the paper fibers; the gelatinization
of the starch combined with the melting of the latex allows the
flowable latex to permeate the paper fibers and impart desirable
properties thereto. In embodiments, the latex-starch composites can
be attached to fibers having low or no attachable affinity for each
other, such as cellulosic fibers and synthetic fibers or two
different populations of synthetic fibers, such that the melting of
the latex allows the flowable latex to attach the fibers to each
other to form a fibrous composite. In embodiments, such a fibrous
composite may have further advantageous properties based, for
example, on the elastomeric nature of the latex agent binding the
fibers together. In other embodiments, the activation-tethering
system disclosed herein can be applied to attach dissimilar types
of cellulose fibers together, such as softwood fibers and hardwood
fibers.
[0065] Most papers and paperboards attain specific physical
characteristics by using a mixture of hardwood and softwood.
Hardwood fibers are short in length, typically around 1 mm and with
a diameter of around 20 um, resulting in a length to diameter ratio
of 50:1. Softwood fibers are longer than hardwood, typically around
3 mm in length with a diameter of 30 um, resulting in a length to
diameter ratio of 100:1. Softwood fibers offer high strength
because of their ability to overlap and intertwine. Hardwood fibers
offer good formation and improve aesthetics of the paper surface
due to their small size. For a functional paper it is necessary to
have adequate wet strength when it is made such that it does not
break on the web and have sufficient mechanical properties (such as
tensile and burst) that it could be used in its intended
application (printing, photocopying for office pares and edge crush
strength, stiffness and bulk for packaging applications). These
mechanical properties are realized when the hardwood and softwood
fibers are intimately mixed together and there is sufficient
hydrogen bonding between them to enable strength and stiffness. To
improve the low number of hydrogen bonds between the fibers, it is
necessary to increase proximity of fibers and the number of contact
points between them.
[0066] To achieve this, softwood fibers are subjected to refining
processes that enhance their surface area, induces fibrillation and
overall improves the contact area between hardwood and softwood
fibers. Refining crushes the lumens of softwood cellulose fibers,
changing them from a cylindrical shape into a ribbon shape. There
are several benefits to refining: the flat fibers result in a
flatter paper surface; the fibrils created from refining result in
more sites for hydrogen bonding; the ratio of softwood and hardwood
can be variably adjusted as necessary because of the increase in
hydrogen bonding and good bond formation. Without refining,
softwood fibers have a low attachable affinity to hardwood fibers.
Refining, by increasing the surface area available for hydrogen
bonding in the softwood fibers, improves the attachable affinity of
softwood fibers to hardwood fibers so that they can be attached to
each other to form functional paper products.
[0067] But refining also creates problems: the increased hydrogen
bonding causes poor drainage on the paper machine; the additional
residence time in a refiner is costly; the crushed lumen results in
a significant decrease in caliper per basis weight. Thus there
exists a need to improve the bonding between hardwood and softwood
fibers without employing the refining process, or with less
intensive refining. Techniques as disclosed herein, described in
more detail below, can attach the dissimilar hardwood and softwood
fibers to each other without refining, thereby decreasing or
eliminating the exposure of the fibers to the refining process.
[0068] Hardwood fibers and unrefined softwood fibers are examples
of dissimilar fibers having low attachable affinity to each other.
In embodiments, other fibers dissimilar to cellulosic fibers can be
introduced into the paper product to improve functionalities and
attain certain features. Certain of these dissimilar fibers can
have a low attachable affinity for the cellulosic fibers, such that
the fibers do not coalesce during papermaking to make a functional
paper product (i.e., one having adequate wet strength when it is
made such that it does not break on the web and having sufficient
mechanical properties (e.g., tensile and burst strength) allowing
it to be used its intended application). Examples of dissimilar
fibers having a low attachable affinity to cellulosic fibers can
include vegetable stalk fibers, bast fibers and seed hull fibers.
Vegetable stalk fibers such as sugarcane, bamboo, cereal straw
(wheat, rye, oats, barley, rice), switchgrass, papyrus, corn,
cotton, and sorghum have length to diameter ratios similar to
softwood or hardwood, but often with high variation and have a high
proportion of thin-walled cells. Bast fibers such as hemp, jute,
kenaf, and flax are significantly more robust than stalk fibers but
still have a high variation of length and diameter. Vegetable stalk
and bast fibers are relatively inexpensive and most require only a
year to reach full maturity (compared to wood which is in the range
of 15-50 years). Economically, it would be advantageous to use
vegetable stalk and bast fibers as fillers in combination with
cellulosic fibers to form paper products. Use of the systems and
methods disclosed herein can allow these fibers (e.g., vegetable
stalk and bast fibers) having low attachable affinity to be formed
into paper products with cellulosic fibers. As used herein, the
term "low attachable affinity" also applies to fibers that have no
attachable affinity to each other.
[0069] Dissimilar populations of fibers, such as a population of
hardwood fibers and a population of softwood fibers, or a
population of cellulosic fibers and a population of non-cellulosic
(natural or synthetic) fibers can be attached to each other by
treating one population with an activator, and the other population
with a tethering agent, and combining the two treated populations.
Dissimilar fibers where the native attachment of one fiber
population to the other fiber population does not allow the two
populations to coalesce during papermaking to make a functional
paper product (i.e., one having adequate wet strength when it is
made such that it does not break on the web and having sufficient
mechanical properties (e.g., tensile and burst strength) allowing
it to be used its intended application) are considered to be fiber
populations having low attachable affinity. At the low end of the
attachable affinity continuum are those fibers, such as cellulosic
and hydrophobic synthetic fibers (e.g., olefinic, polyamide,
polyester fibers, and the like) that have minimal or no attachable
affinity for each other.
[0070] The interaction of the activator and the tethering agent
forms a durable complex binding the two dissimilar fiber
populations together, overcoming the tendency of fiber populations
with low attachable affinity to form inadequate paper products, and
reinforcing the attachment of fiber populations with a higher
attachable affinity to each other. In an exemplary embodiment of
two populations of dissimilar fibers with low attachable affinity,
hardwood fibers can be treated with a tethering agent and softwood
fibers can be treated with an activator, or vice versa. Using the
activator-tether system in this way can save the time, energy and
expense associated with processing the softwood fibers as is
currently done. These two treated populations can be combined to
form a paper product, attaching the hardwood and the softwood
fibers together without the need to subject the softwood fibers to
the refining process. Similarly, cellulosic fibers can be treated
with an activator, and hydrophobic synthetic fibers can be treated
with a tethering agent or vice versa: this represents another
example of two dissimilar fiber populations having low or no
attachable affinity to each other.
[0071] These two treated populations of dissimilar fibers can be
combined to form a paper product, attaching (for example) the
cellulosic and the non-cellulosic fibers together to form a paper
product having specialized properties. As an example, cotton seed
hull fibers (both staple and linter) are significantly longer than
softwood fibers with relatively low variability in length and
diameter, and can offer high strength to specialty papers (i.e.
currency), but are very expensive. Hull fibers, typically high in
lignin and/or inorganic content are dissimilar to cellulose, and
they represent low affinity attachable fibers. Their attachment to
cellulosic fibers can be improved by using the systems and methods
disclosed herein, allowing fewer of these fibers to be used for
forming a high performance product. Advantageously, hull fibers can
be used as high performance additives, in combination with
cellulosic fibers to form paper products.
[0072] For papermaking, cationic and anionic polymers for
activators and tethering agents (respectively) can be selected from
a wide variety of available polymers, as described above. In
embodiments, starch granules used to form starch-latex composites
can be used in their native state, or they can be modified with
short amine side-groups, with amine polymers, or with hydrophobic
side groups (each a "modified starch"). The presence of amines on
the surface of the starch granules can help in attaching an anionic
tethering polymer.
[0073] For activating the cellulose fibers, cationic polymers can
be used. The polycation can be linked to the fiber surface using a
coupling agent, for example a bifunctional crosslinking agent such
as a carbonyldiimidazole or a silane, or the polyamine can
self-assemble onto the surface of the cellulose fiber through
electrostatic, hydrogen bonding, or hydrophobic interactions. In
embodiments, the polyamine can spontaneously self-assemble onto the
fiber surface or it can be precipitated onto the surface. For
example, in embodiments, chitosan can be precipitated on the
surface of the cellulose fibers to activate them. Because chitosan
is soluble only in an acidic solution, it can be added to a
cellulose fiber dispersion at an acidic pH, and then can be
precipitated onto the surface of the cellulose fibers by slowly
adding base to the dispersion until chitosan is no longer soluble.
In embodiments, a difunctional crosslinking agent can be used to
attach the polycation to the fiber, by reacting with both the
polycation and the fiber.
[0074] In other embodiments, a polycation such as a polyamine can
be added directly to the fiber dispersion or slurry. For example,
the addition level of the polycation can be between about 0.01% to
5.0% (based on the weight of the fiber), e.g., between 0.1% to 2%.
For example, if the cellulose fiber population is treated with a
polyamine like poly(DADMAC), a separately treated population of
tether-bearing starch granules can be mixed in thereafter,
resulting in the attachment of the starch-latex composites to the
cellulose fibers by the interaction of the activator polymer and
the tether polymer. In embodiments, starch-latex composites can be
treated with a variety of anionic polymers, such as anionic
polyacrylamide, which then act as tethers.
[0075] Starch that is to be treated in accordance with these
systems and methods can be further derivatized or coated with
moieties that impart desirable properties, e.g., hydrophobicity,
oleophobicity or both. Starches thus modified may be also termed
"modified starches." Preferred oil resistant coating formulations
are aqueous solutions of cellulose derivatives such as
methylcellulose, ethyl cellulose, propyl cellulose, hydroxypropyl
methyl cellulose, hydroxyethyl methyl cellulose, ethylhydroxypropyl
cellulose, and ethylhydroxyethyl cellulose, cellulose acetate
butyrate, which may further comprise polyvinyl alcohol and/or its
derivatives. Another group of preferred oil resistant coating
compositions are latex emulsions such as the emulsions of
polystyrene, styrene-acrylonitrile copolymer, carboxylated
styrene-butadiene copolymer, ethylene-vinyl chloride copolymer,
styrene-acrylic copolymer, polyvinyl acetate, ethylene-vinyl
acetate copolymer, and vinyl acetate-acrylic copolymer. The starch
granule thus coated with grease resistant formulations could be
attached to the activated pulp fibers via tethering, such that the
surface segregation of the starch granule will modify the surface
of the paper product.
[0076] In embodiments, the presence of hydrophobic starch also
improves the hydrophobicity of the resulting paper without needing
an internal sizing such as alkyl succinic anhydride (ASA), alkyl
ketene dimer (AKD) or Rosin. The gelatinized hydrophobic starch
sizes the entire thickness of the paper. This property is useful in
reducing the coating requirements in making coated sheets. The
coating applied using a roller or a metering bar or any such
methods, would remain on the surface of the paper and not
impregnate the bulk of the paper thus needing less coating to
achieve the same amount of gloss and surface finish.
[0077] In other embodiments, the addition of a coating agent to the
starch can improve its mechanical properties such as bending
stiffness or tensile strength, or could improve its optical
properties (e.g., TiO2 nanoparticles bound to starch).
EXAMPLES
[0078] Materials [0079] Market softwood and hardwood pulp [0080]
Recycled brown pulp [0081] Unrefined softwood and hardwood pulp
[0082] Poly(diallyldimethylammonium chloride), Hi Molecular Weight,
20 wt % in water (polyDADMAC), Sigma-Aldrich, St. Louis, Mo. [0083]
MagnaFloc 919, Ciba Specialty Chemicals Corporation, Suffolk, Va.
[0084] STA-LOK 300 Starch, Tate & Lyle, Decatur, Ill. (cationic
starch) [0085] COSEAL 30061A Anionic Latex, Rohm & Haas,
Philedelphia, Pa. [0086] ChitoClear Chitosan CG-10, Primex,
Siglufjordur, Iceland [0087] Polyethylene fibers PEFYB-00620,
MiniFibers, Inc., Johnson City, Tenn. [0088] Modified Polyethylene
fibers PEFYB-ONL490, MiniFibers, Inc., Johnson City, Tenn. [0089]
Polypropylene fibers ("PP"), PEFYB-00Y600, MiniFibers, Inc.,
Johnson City, Tenn. [0090] PES/Nylon pie wedge bicomponent cut
fibers [0091] Precipitated Calcium Carbonate (PCC), Sigma-Aldrich,
St. Louis, Mo. [0092] Douglas Pearl Starch (unmodified corn
starch), Penford Products, Cedar Rapids, Iowa [0093] Iron (III)
Oxide, <5 um, 99.9%, Sigma-Aldrich, St. Louis, Mo.
Example 1
Control Virgin Pulp
[0094] A 0.5% slurry was prepared by blending 3.5% by weight
softwood and hardwood pulp mixture (in the ratio of 20:80) in
water.
Example 2
Control Recycled Pulp
[0095] A 0.5% slurry was prepared by blending 22.5% recycled brown
pulp in water.
Example 3
Handsheet Preparation
[0096] Handsheets were prepared using a Mark V Dynamic Paper
Chemistry Jar and HandSheet Mold from Paper Chemistry Laboratory,
Inc. (Larchmont, N.Y.). Handsheets were prepared without addition
of polymers as controls, using the pulps prepared as described in
Example 1 and 2. Handsheets were prepared with the addition of
polymers as experimental samples, as described below.
[0097] For preparing each experimental handsheet, the appropriate
volume of 0.5% pulp slurry prepared in accordance with Examples 1
or 2 (as applicable) was activated with up to 2% of the selected
polymer(s) (based on dry weight), as described below in more
detail. Polymer additions were performed at 5 minute intervals.
This polymer-containing slurry was diluted with up to 3 L of water
and added to the handsheet maker, where it was mixed at a rate of
1100 RPM for 5 seconds, 700 RPM for 5 seconds, and 400 RPM for 5
seconds. The water was then drained off. The subsequent sheet was
then transferred off of the wire, pressed and dried.
[0098] For preparing sheets containing low melting point synthetic
fibers PEFYB-00620, PEFYB-ONL490, PEFYB-00Y600, as described below
in Example 9, the sheets were dried as described above and then
heated further to ensure melting of the synthetic fibers.
Example 4
Tensile Test
[0099] Tensile tests were conducted on control and experimental
samples using an Instron 3343. Samples of handsheets for tensile
testing were initially cut into 1 in wide strips with a paper
cutter, and then attached within the Instron 3343. The gauge length
region was set at 4 in and the crosshead speed was 1 in/minute.
Thickness was measured to provide stress data as was the weight to
be able to normalize the data by weight of samples. The strips were
tested to failure with an appropriate load cell. At least three
strips from each control or experimental handsheet sample were
tested and the values were averaged together.
Example 5
Preparation of Latex-Coated Starch without Tether
[0100] StaLok 300 cationic starch was dispersed in water in slurry
form such that the solids content was about 20%. COSEAL 30061A
anionic latex was added to the cationic starch, up to 50% by weight
of starch. The latex is spontaneously self-assembled on the starch
surface resulting in a clear solution when the starch settles down.
By contrast, the latex solution without starch remains milky white,
as shown in FIG. 1.
Example 6
Preparation Of Latex-Coated Starch With Tether
[0101] StaLok 300 cationic starch was dispersed in water in slurry
form such that the solids content was about 20%. COSEAL 30061A
anionic latex was added to the cationic starch, up to 50% by weight
of starch. Latex-coated starch composite particles were formed,
which acted as "anchor particles." MagnaFloc 919 was then added
0.1% by weight as a tethering agent.
Example 7
Process for Preparing Handsheets from Activated Pulp and
Latex-Coated Starch (with and without Tether)
[0102] 800 mL of a 0.5% pulp slurry prepared in accordance with
Example 1 or 2 (as applicable) was initially provided. The pulp
slurry was activated with 0.1% by fiber weight polyDADMAC.
Separately, latex-coated cationic starch granules were prepared as
a slurry in accordance with Example 5 (i.e., a non-tether-bearing
starch slurry), and tethered latex-coated cationic starch granules
were prepared as a slurry in accordance with Example 6 (i.e., a
tether-bearing starch slurry). Each slurry was mixed for 5 minutes
individually and then the pulp slurry was combined with a
non-tether-bearing or a tether-bearing starch slurry and mixed for
another 5 minutes using an overhead stirrer. Handsheets were then
produced by the method in Example 3. The final basis weight was
approximately 80 gsm for these handsheets.
Example 8
Preparation of Synthetic Fibers with and without Tether
[0103] PEFYB-00620, PEFYB-0NL490, PEFYB-00Y600, and PES/Nylon
Bicomponent Fibers (and mixtures of two or more of the previous)
were dispersed in water in slurry form such that the solids content
was about 20%. In samples containing a tether, MagnaFloc 919 was
then added 0.1% by weight as a tethering agent.
Example 9
Process for Preparing Handsheets from Activated Pulp and Tethered
Synthetic Fibers
[0104] 800 mL of a 0.5% pulp slurry prepared in accordance with
Example 1 or 2 (as applicable) was initially provided. The pulp
slurry was activated with 0.1% by fiber weight polyDADMAC.
Separately, synthetic fibers with and with and without tethers were
prepared in accordance with Example 8, so that their performance
could be compared with the performance of the samples prepared with
the activated pulp and tethered synthetic fibers. Each slurry was
mixed for 5 minutes and then combined and mixed for another 5
minutes using an overhead stirrer. Handsheets were then produced by
the method in Example 3. The final basis weight was approximately
80 gsm for these handsheets.
Example 10
Preparation of Chitosan Solution
[0105] CG-10 was added to water to make a 1% by weight slurry of
chitosan. Strong acid was added dropwise to the slurry with
stirring until the solution reached a pH of 2.5 and the chitosan
was dissolved.
Example 11
Preparation Of Coated Synthetic Fibers With Chitosan
[0106] PEFYB-00620, PEFYB-0NL490, PEFYB-00Y600, and PES/Nylon
Bicomponent Fibers (and mixtures of two or more of the previous)
were dispersed in water in slurry form such that the solids content
was about 20%. A strong acid was then added to the slurry to bring
the pH below 2.5. The solution in Example 10 was added to the
synthetic fiber slurry so that the chitosan was 1% by weight of the
synthetic fibers. The pH was then raised back to 8-9 with a strong
base to precipitate any unbound chitosan.
Example 12
Process for Preparing Handsheets from Pulp and Chitosan-Coated
Synthetic Fibers
[0107] 800 mL of a 0.5% pulp slurry prepared in accordance with
Example 1 or 2 (as applicable) was initially provided. Separately,
chitosan-coated synthetic fibers were prepared as a slurry in
accordance with Example 11, where chitosan exemplifies a tethering
agent. Each slurry preparation was mixed for 5 minutes, then
samples of the uncoated pulp slurry were combined with the
chitosan-coated synthetic fibers slurry and mixed for another 5
minutes using an overhead stirrer. Handsheets were then produced by
the method in Example 3. The final basis weight was approximately
80 gsm for these handsheets.
Example 13
The Effect of Latex-Coated Starch on Strength and
Hydrophobicity
[0108] Handsheet samples were prepared from activated pulp in
accordance with Example 7, where the amount of latex-coated and
tether-bearing latex-coated starch (StaLok 300) was 4.25% of the
solids weight. The latex-coated starch had been coated with COSEAL
30061A in accordance with Example 5. The tether-bearing
latex-coated starch had been coated with COSEAL30061A and then
tethered with MagnaFloc 919 in accordance with Example 6. Control
handsheets were also prepared in accordance with Example 3 (no
activation) using the latex-coated starch particles of Example 5
(no tether). Strength data was gathered from handsheet samples made
with: (1) activated pulp and tether-bearing latex-coated samples
("ATA treated"), (2) activated pulp and non-tether-bearing
latex-coated particles, and (3) non-activated pulp and
non-tether-bearing latex-coated particles. For ATA-treated samples,
the tether used on the starch was 0.1% MagnaFloc 919 by solids and
the activator on the pulp was 0.1% polyDADMAC by solids. The max
load for each sample was measured using an Instron as in Example 4.
Data were normalized by the mass to show load contribution per
overall solids weight. Graph 1 (FIG. 2) shows the strength data
with all of the aforementioned conditions mentioned in this
example. FIG. 2 shows a graph of normalized max. load examining the
effect of pulp with and without latex-coated starch and with and
without the use of ATA treatment. Measurements of the tensile load
at failure are comparable between samples showing that the presence
of latex has not weakened the sheet due to the presence of
tethering and anchoring chemistries.
[0109] The hydrophobicity improvement with the samples above was
also examined. Using handsheet samples prepared as in Example 7,
hydrophobicity was tested by depositing a 25 microliter water
droplet on the surface of the paper and recording the time for the
droplet to completely absorbed by the paper. The results of the
hydrophobicity tests are shown in Table 1 (FIG. 3). FIG. 3 shows a
table of normalized water droplet holdout examining the effect of
pulp with and without latex-coated starch and with and without the
use of ATA. These results demonstrate that the use of the ATA
process (and activator-only) to attach latex-coated starch to pulp
fibers improves the water resistance of the paper by up to 14,500%
compared to control samples having no added latex-coated
starch.
Example 14
The Effect of Tethered Synthetic Fibers on Strength and
Hydrophobicity
[0110] Samples were prepared as in Example 9, where the amount of
tether-bearing synthetic fibers were a total of 15% of the solids
weight. The tether-bearing synthetic fibers had been prepared in
accordance with Example 8. Samples were made both with activator
and tether and without either activator or tether. For ATA-treated
samples, the tether used on the synthetic fibers was 0.1% MagnaFloc
919 by solids and the activator on the pulp was 0.1% polyDADMAC by
solids. The max load for each sample was measured using an Instron
as in Example 4. Data were normalized by the mass to show load
contribution per overall solids weight. Graph 2 (FIG. 4) shows the
strength data with all of the aforementioned conditions mentioned
in this example.
[0111] FIG. 4 shows a graph of normalized max. load examining the
effect of pulp with and without synthetic fibers and with and
without the use of ATA. Normalized tensile load at failure for the
samples show that there is no significant loss in tensile strength
due to inclusion of the synthetic fibers. The hydrophobicity
improvement with the samples above was also examined. Using fiber
handsheet samples prepared as in Example 9, hydrophobicity was
tested by depositing a 25 microliter water droplet on the surface
of the paper and recording the time for the droplet to completely
absorbed by the paper. The results of the hydrophobicity tests are
shown in Table 2 (FIG. 5). These results demonstrate that the use
of synthetic fibers in combination with pulp fibers improves the
water resistance of the paper by up to 26,600% compared to control
samples having no added synthetic fibers. FIG. 5 shows a table of
normalized water droplet holdout examining the effect of pulp with
and without synthetic fibers and with and without the use of ATA.
Water droplet holdout times show that there is a >266.times.
gain in droplet holdout time with the use of polypropylene fibers
under several conditions.
Example 15
The Effect of Chitosan-Coated Synthetic Fibers on Strength and
Hydrophobicity
[0112] Samples were prepared as in Example 12, where the amount of
chitosan-coated synthetic fibers were a total of 15% of the solids
weight. The chitosan-coated synthetic fibers had been prepared in
accordance with Example 11. The max load for each sample was
measured using an Instron as in Example 4. Data were normalized by
the mass to show load contribution per overall solids weight. Graph
3 (FIG. 6) shows the strength data with all of the aforementioned
conditions mentioned in this example. FIG. 6 shows a graph of
normalized max. load examining the effect of pulp with synthetic
fibers with and without the use of chitosan. Normalized tensile
load at failure for the samples show that there is no significant
loss in tensile strength due to inclusion of the synthetic fibers.
The hydrophobicity improvement with the samples above was also
examined. Using recycled fiber handsheet samples prepared as in
Example 12, hydrophobicity was tested by depositing a 25 microliter
water droplet on the surface of the paper and recording the time
for the droplet to completely absorbed by the paper. The results of
the hydrophobicity tests are shown in Table 3 (FIG. 7). These
results demonstrate that the use of chitosan-coated synthetic
fibers improves the water resistance of the paper by up to 26,600%
compared to control samples having no synthetic fibers. FIG. 7
shows a table of normalized water droplet holdout examining the
effect of pulp with and without synthetic fibers and with and
without chitosan coating. Water droplet holdout times show that
there is a >266.times. gain in droplet holdout time with the use
of polypropylene fibers coated with chitosan.
Example 16
Control Virgin Pulp (Softwood Only)
[0113] A 0.5% slurry was prepared by blending 93% solids content
softwood in water.
Example 17
Preparation of PCC and Pearl Starch with and without Tether
[0114] PCC and Pearl Starch (and mixtures of the two) were
dispersed in water in slurry form such that the solids content was
about 20%. In samples containing a tether, MagnaFloc 919 was then
added 0.05% by weight of solids as a tethering agent.
Example 18
Preparation of a Handsheet with PCC and Pearl Starch
[0115] 600 mL of a 0.5% pulp slurry prepared in accordance with
Example 16 was initially provided. The pulp slurry was activated
with 0.1% by fiber weight polyDADMAC. Separately, starch, PCC, and
tethered starch/PCC were prepared as a slurry in accordance with
Example 17. Each slurry was mixed for 5 minutes and then combined
and mixed for another 5 minutes using an overhead stirrer.
Handsheets were then produced by the method in Example 16. The
final basis weight was approximately 60 gsm for these
handsheets.
Example 19
The Effect of PCC and Pearl Starch on Strength
[0116] Samples were prepared as in Example 18, where the amount of
PCC, Pearl Starch, tether-bearing pearl starch and PCC was between
5% and 30% of the solids weight. The tethered PCC with pearl starch
had been prepared with MagnaFloc 919 in accordance with Example 17.
Samples were made with both activator and tether or with neither
activator nor tether. For ATA-treated samples, the tether used on
the dry-mixed pearl starch and PCC and was 0.05% MagnaFloc 919 by
solids and the activator on the pulp was 0.1% polyDADMAC by solids.
The max load for each sample was measured using an Instron as in
Example 16. Data were normalized by the mass to show load
contribution per overall solids weight. Graph 4 (FIG. 8) shows the
strength data with all of the aforementioned conditions mentioned
in this example. As shown in FIG. 8, the ATA treatment improves
retention and reduces the loss of tensile strength at similar
loadings of PCC.
Example 20
Preparation of Iron (III) Oxide with and without Tether
[0117] Iron (III) Oxide particles were dispersed in water in slurry
form such that the solids content was about 20%. In samples
containing a tether, MagnaFloc 919 was then added 0.05% by weight
of solids as a tethering agent.
Example 21
Preparation of a Handsheet with Iron (III) Oxide
[0118] 600 mL of a 0.5% pulp slurry prepared in accordance with
Example 16 was initially provided. The pulp slurry was activated
with 0.1% by fiber weight polyDADMAC. Separately, Iron (III) Oxide
with and without tether were prepared as a slurry in accordance
with Example 20. Each slurry was mixed for 5 minutes and then
combined and mixed for another 5 minutes using an overhead stirrer.
Handsheets were then produced by the method in Example 16. The
final basis weight was approximately 60 gsm for these
handsheets.
Example 22
Analysis of Magnetization of Iron (III) Oxide Handsheets
[0119] 1'' by 2'' pieces of handsheets with iron (III) oxide
prepared in Example 21 were held to a ceramic magnet to verify
holdout of Iron (III) Oxide in the sheet. Sheets containing as
little as 5% Iron (III) oxide by solids weight held onto the magnet
with no other support.
Example 23
Preparation of Softwood Pulp with Polymer Activator
[0120] 3.5% solids unrefined softwood pulp was diluted with water
to 1% solids. 0.1% polyDADMAC by weight of softwood solids was
added to the slurry and mixed gently for 30 seconds. The activated
slurry was then diluted with water down to 0.5% solids.
Example 24
Preparation of Hardwood Pulp with Polymer Tether
[0121] 3.5% solids unrefined hardwood pulp was diluted with water
to 1% solids. 0.1% MagnaFloc 919 by weight of hardwood solids was
added to the slurry and mixed gently for 30 seconds. The tethered
slurry was then diluted with water down to 0.5% solids.
Example 25
Process for Preparing Handsheets from Activated Softwood and
Tethered Hardwood Pulp
[0122] 260 mL each of 0.5% solids activated softwood and tethered
hardwood pulp as described in Examples 5 and 6 were combined and
mixed for 5 minutes. Handsheets were then produced by the method in
Example 3. The final basis weight was approximately 80 gsm for
these handsheets.
[0123] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *