Note: Descriptions are shown in the official language in which they were submitted.
CA 02603476 2007-09-20
MIXED POLYMER SUPERABSORBENT FIBERS CONTAINING CELLULOSE
BACKGROUND OF THE INVENTION
Personal care absorbent products, such as infant diapers, adult incontinent
pads,
and feminine care products, typically contain an absorbent core that includes
superabsorbent polymer particles distributed within a fibrous matrix.
Superabsorbents
are water-swellable, generally water-insoluble absorbent materials having a
high
absorbent capacity for body fluids. Superabsorbent polymers (SAPs) in common
use are
mostly derived from acrylic acid, which is itself derived from petroleum oil,
a
non-renewable raw material. Acrylic acid polymers and SAPs are generally
recognized
as not being biodegradable. Despite their wide use, some segments of the
absorbent
products market are concerned about the use of non-renewable petroleum oil
derived
materials and their non-biodegradable nature. Acrylic acid based polymers also
comprise
a meaningful portion of the cost structure of diapers and incontinent pads.
Users of SAP
are interested in lower cost SAPs. The high cost derives in part from the cost
structure
for the manufacture of acrylic acid which, in turn, depends upon the
fluctuating price of
petroleum oil. Also, when diapers are discarded after use they normally
contain
considerably less than their maximum or theoretical content of body fluids. In
other
words, in terms of their fluid holding capacity, they are "over-designed".
This
"over-design" constitutes an inefficiency in the use of SAP. The inefficiency
results in
part from the fact that SAPs are designed to have high gel strength (as
demonstrated by
high absorbency under load or AUL). The high gel strength (upon swelling) of
currently
used SAP particles helps them to retain a lot of void space between particles,
which is
helpful for rapid fluid uptake. However, this high "void volume"
simultaneously results
in there being a lot of interstitial (between particle) liquid in the product
in the saturated
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state. When there is a lot of interstitial liquid the "rewet" value or "wet
feeling" of an
absorbent product is compromised.
In personal care absorbent products, U.S. southern pine fluff pulp is commonly
used in conjunction with the SAP. This fluff is recognized worldwide as the
preferred
fiber for absorbent products. The preference is based on the fluff pulp's
advantageous
high fiber length (about 2.8 mm) and its relative ease of processing from a
wetland pulp
sheet to an airlaid web. Fluff pulp is also made from renewable and
biodegradable
cellulose pulp fibers. Compared to SAP, these fibers are inexpensive on a per
mass basis,
but tend to be more expensive on a per unit of liquid held basis. These fluff
pulp fibers
mostly absorb within the interstices between fibers. For this reason, a
fibrous matrix
readily releases acquired liquid on application of pressure. The tendency to
release
acquired liquid can result in significant skin wetness during use of an
absorbent product
that includes a core formed exclusively from cellulosic fibers. Such products
also tend to
leak acquired liquid because liquid is not effectively retained in such a
fibrous absorbent
core.
Superabsorbent produced in fiber form has a distinct advantage over particle
forms in some applications. Such superabsorbent fiber can be made into a pad
form
without added non superabsorbent fiber. Such pads will also be less bulky due
to
elimination or reduction of the non superabsorbent fiber used. Liquid
acquisition will be
more uniform compared to a fiber pad with shifting superabsorbent particles.
A need therefore exists for a fibrous superabsorbent material that is
simultaneously made from a biodegradable renewable resource like cellulose
that is
inexpensive. In this way, the superabsorbent material can be used in absorbent
product
designs that are efficient. These and other objectives are accomplished by the
invention
set forth below.
SUMMARY OF THE INVENTION
The invention provides a mixed polymer composite fiber that includes a
carboxyalkyl cellulose, a galactomannan polymer or a glucomannan polymer, and
cellulose fiber. The mixed polymer composite fibers includes a plurality of
non-permanent intra-fiber metal crosslinks.
The invention also provides a method for making mixed polymer composite fibers
containing cellulose. The method includes the steps of dispersing cellulose
fibers in an
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aqueous solution comprising a carboxyalkyl cellulose and a galactomannan
polymer or a
glucomannan polymer in water to provide an aqueous fiber dispersion; treating
the
aqueous dispersion with a first crosslinking agent to provide a gel; mixing
the gel with a
water-miscible solvent to provide composite fibers; and treating the composite
fibers with
a second crosslinking agent to provide crosslinked fibers.
DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention
will
become more readily appreciated as the same become better understood by
reference to
the following detailed description, when taken in conjunction with the
accompanying
drawings, wherein:
FIGURE 1 is a photograph of representative mixed polymer composite fibers of
the invention;
FIGURE 2 is a photograph of representative mixed polymer composite fibers of
the invention; and
FIGURE 3 is a scanning electron microscope photograph (1000x) of
representative mixed polymer composite fibers of the invention (cross-
section).
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a mixed polymer composite fiber. The present
invention provides methods for making the mixed polymer composite fiber..
The mixed polymer composite fiber is a fiber comprising a carboxyalkyl
cellulose, a galactomannan polymer or a glucomannan polymer, and cellulose.
The
carboxyalkyl cellulose, which is mainly in the sodium salt form, can be in
other salts
forms such as potassium and ammonium forms. The mixed polymer composite fiber
is
formed by intermolecular crosslinking of mixed polymer molecules, and is water
insoluble and water-swellable.
In one aspect, the present invention provides a mixed polymer composite fiber
that further includes cellulose. As used herein, the term "mixed polymer
composite fiber"
refers to a fiber that is the composite of at least three different polymers
(i.e., mixed
polymer). The mixed polymer composite fiber is a homogeneous composition that
includes two associated water-soluble polymers: (1) a carboxyalkyl cellulose
and
(2) either a galactomannan polymer or a glucomannan polymer.
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The carboxyalkyl cellulose useful in making the mixed polymer composite fiber
has a degree of carboxyl group substitution (DS) of from about 0.3 to about
2.5. In one
embodiment, the carboxyalkyl cellulose has a degree of carboxyl group
substitution of
from about 0.5 to about 1.5.
Although a variety of carboxyalkyl celluloses are suitable for use in making
the
mixed polymer composite fiber, in one embodiment, the carboxyalkyl cellulose
is
carboxymethyl cellulose. In another embodiment, the carboxyalkyl cellulose is
carboxyethyl cellulose.
The carboxyalkyl cellulose is present in the mixed polymer composite fiber in
an
amount from about 60 to about 99% by weight based on the weight of the mixed
polymer
composite fiber. In one embodiment, the carboxyalkyl cellulose is present in
an amount
from about 80 to about 95% by weight based on the weight of the mixed polymer
composite fiber. In addition to carboxyalkyl cellulose derived from wood pulp
containing some carboxyalkyl hemicellulose, carboxyalkyl cellulose derived
from non-
wood pulp, such as cotton linters, is suitable for preparing the mixed polymer
composite
fiber. For carboxyalkyl cellulose derived from wood products, the mixed
polymer fibers
include carboxyalkyl hemicellulose in an amount up to about 20% by weight
based on the
weight of the mixed polymer composite fiber.
The galactomannan polymer useful in making the mixed polymer composite fiber
of the invention can include any one of a variety of galactomannan polymers.
In one
embodiment, the galactomannan polymer is guar gum. In another embodiment, the
galactomannan polymer is locust bean gum. In a further embodiment, the
galactomannan
polymer is tara gum.
The glucomannan polymer useful in making the mixed polymer composite fiber
of the invention can include any one of a variety of glucomannan polymers. In
one
embodiment, the glucomannan polymer is konjac gum. In another embodiment, the
galactomannan polymer is locust bean gum. In a further embodiment, the
galactomannan
polymer is tara gum.
The galactomannan polymer or glucomannan polymer is present in an amount
from about 1 to about 20% by weight based on the weight of the mixed polymer
composite fiber. In one embodiment, the galactomannan polymer or glucomannan
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polymer is present in an amount from about 1 to about 15% by weight based on
the
weight of the mixed polymer composite fiber.
The cellulose is present in an amount from about 2 to about 15% by weight
based
on the weight of the mixed polymer composite fiber. In one embodiment, the
cellulose is
present in an amount from about 5 to about 10% by weight based on the weight
of the
mixed polymer composite fiber.
Although available from other sources, suitable cellulosic fibers are derived
primarily from wood pulp. Suitable wood pulp fibers for use with the invention
can be
obtained from well-known chemical processes such as the kraft and sulfite
processes,
with or without subsequent bleaching. Pulp fibers can also be processed by
thermomechanical, chemithermomechanical methods, or combinations thereof. A
high
alpha cellulose pulp is also a suitable wood pulp fiber. The preferred pulp
fiber is
produced by chemical methods. Ground wood fibers, recycled or secondary wood
pulp
fibers, and bleached and unbleached wood pulp fibers can be used. Softwoods
and
hardwoods can be used. Suitable fibers are commercially available from a
number of
companies, including Weyerhaeuser Company. For example, suitable cellulosic
fibers
produced from southern pine that are usable with the present invention are
available from
Weyerhaeuser Company under the designations CF416, NF405, PL416, FR516, and
NB416. Other suitable fibers include northern softwood and eucalyptus fibers.
The preparation of the mixed polymer composite fiber is a multistep process.
First, the water-soluble carboxyalkyl __cellulose and galactomannan polymer or
glucomannan polymer are dissolved in water to provide a polymer solution.
Cellulose
fiber is then added and dispersed in the polymer solution. Then, a first
crosslinking agent
is added and mixed to obtain a mixed polymer composite gel formed by
intermolecular
crosslinking of water-soluble polymers intimately associated with dispersed
cellulose
fiber.
Suitable first crosslinking agents include crosslinking agents that are
reactive
towards hydroxyl groups and carboxyl groups. Representative crosslinking
agents
include metallic crosslinking agents, such as aluminum (III) compounds,
titanium (IV)
compounds, bismuth (III) compounds, boron (III) compounds, and zirconium (IV)
compounds. The numerals in parentheses in the preceding list of metallic
crosslinking
agents refers to the valency of the metal.
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The mixed polymer composite fiber is generated by rapid mixing of the mixed
polymer composite gel with a water-miscible solvent. This fiber generated
after first
crosslinking has a high level of sliminess when hydrated and forms soft gels.
Therefore
this fiber cannot be used in absorbent applications without further treatment.
The mixed
polymer composite fiber thus obtained is further crosslinked (e.g., surface
crosslinked) by
treating with a second crosslinking agent in a water-miscible solvent
containing water.
The composition of water-miscible solvent and water is such that the fiber
does not
change its fiber form and return to gel state. The second crosslinking agent
can be the
same as or different from the first crosslinking agent.
The mixed polymer fibers of the invention are substantially insoluble in water
while being capable of absorbing water. The fibers of the invention are
rendered water
insoluble by virtue of a plurality of non-permanent intra-fiber metal
crosslinks. As used
herein, the term "non-permanent intra-fiber metal crosslinks" refers to the
nature of the
crosslinking that occurs within individual modified fibers of the invention
(i.e., intra-
fiber) and among and between each fiber's constituent polymer molecules.
The fibers of the invention are intra-fiber crosslinked with metal crosslinks.
The
metal crosslinks arise as a consequence of an associative interaction (e.g.,
bonding)
between functional groups on the fiber's polymers (e.g., carboxy, carboxylate,
or
hydroxyl groups) and a multi-valent metal species. Suitable multi-valent metal
species
include metal ions having a valency of three or greater and that are capable
of forming
interpolymer associative interactions with the functional groups of.. the
polymer
(e.g., reactive toward associative interaction with the carboxy, carboxylate,
or hydroxyl
groups). The polymers are crosslinked when the multi-valent metal species form
interpolymer associative interactions with functional groups on the polymers.
A crosslink
may be formed intramolecularly within a polymer or may be formed
intermolecularly
between two or more polymer molecules within a fiber. The extent of
intermolecular
crosslinking affects the water solubility of the composite fibers (i.e., the
greater the
crosslinking, the greater the insolubility) and the ability of the fiber to
swell on contact
with an aqueous liquid.
The fibers of the invention include non-permanent intra-fiber metal crosslinks
formed both intermolecularly and intramolecularly in the population of polymer
molecules. As used herein, the term "non-permanent crosslink" refers to the
metal
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crosslink formed with two or more functional groups of a polymer molecule
(intramolecularly) or formed with two or more functional groups of two or more
polymer
molecules (intermolecularly). It will be appreciated that the process of
dissociating and
re-associating (breaking and reforming crosslinks) the multi-valent metal ion
and polymer
molecules is dynamic and also occurs during liquid acquisition. During water
acquisition
the individual fibers and fiber bundles swell and change to gel state. The
ability of
non-permanent metal crosslinks to dissociate and associate under water
acquisition
imparts greater freedom to the gels to expand than if the gels were
restrictively
crosslinked by permanent crosslinks that do not have the ability to dissociate
and re-
associate. Covalent organic crosslinks, such as ether crosslinks, are
permanent crosslinks
that do not have the ability to dissociate and re-associate.
The fibers of the invention have fiber widths of from about 2 m to about 50
.m
(or greater) and coarseness that varies from soft to rough.
Representative mixed polymer composite fibers of the invention are illustrated
in
FIGURES 1-3. FIGURE 1 is a photograph of representative mixed polymer
composite
fibers of the invention. FIGURE 2 is a photograph of representative mixed
polymer
composite fibers of the invention. FIGURE 3 is a scanning electron microscope
photograph (1000x) of representative mixed polymer composite fibers of the
invention
(cross-sectional view) (Sample 4, Table 1).
The fibers of the invention are highly absorptive fibers. The fibers have a
Free
Swell Capacity of from about 30 to about 60 g/g (0.9% saline solution), a
Centrifuge
Retention Capacity (CRC) of from about 15 to about 35 g/g (0.9% saline
solution), and
an Absorbency Under Load (AUL) of from about 15 to about 30 g/g (0.9% saline
solution).
The fibers of the invention can be formed into pads by conventional methods
including air-laying techniques to provide fibrous pads having a variety of
liquid wicking
characteristics. For example, pads absorb liquid at a rate of from about 10
mLJsec to
about 0.005 mUsec (0.9% saline solution/10 mL application). The integrity of
the pads
can be varied from soft to very strong.
The mixed polymer composite fibers of the present invention are water
insoluble
and water swellable. Water insolubility is imparted to the fiber by
intermolecular
crosslinking of the mixed polymer molecules, and water swellability is
imparted to the
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fiber by the presence of carboxylate anions with associated cations. The
fibers are
characterized as having a relatively high liquid absorbent capacity for water
(e.g., pure
water or aqueous solutions, such as salt solutions or biological solutions
such as urine).
Furthermore, because the mixed polymer fiber has the structure of a fiber, the
mixed
polymer composite fiber also possesses the ability to wick liquids. The mixed
polymer
composite fiber of the invention advantageously has dual properties of high
liquid
absorbent capacity and liquid wicking capacity.
Mixed polymer fibers having slow wicking ability of fluids are useful in
medical
applications, such as wound dressings and others. Mixed polymer fibers having
rapid
wicking capacity for urine are useful in personal care absorbent product
applications.
The mixed polymer fibers can be prepared having a range of wicking properties
from
slow to rapid for water and 0.9% aqueous saline solutions.
The mixed polymer composite fibers of the invention are useful as
superabsorbents in personal care absorbent products (e.g., infant diapers,
feminine care
products and adult incontinence products). Because of their ability to wick
liquids and to
absorb liquids, the mixed polymer composite fibers of the invention are useful
in a
variety of other applications, including, for example, wound dressings, cable
wrap,
absorbent sheets or bags, and packaging materials.
In one aspect of the invention, methods for making mixed polymer composite
fibers are provided.
In one embodiment, the method for making the mixed polymer composite fibers
includes the steps of: (a) dissolving carboxyalkyl cellulose (e.g., mainly in
salt form,
with or without carboxyalkyl hemicellulose) and a galactomannan polymer or a
glucomannan polymer in water to provide an aqueous polymer solution; (b)
dispersing
cellulose fibers in the polymer solution to provide an aqueous fiber
dispersion;
(c) treating the aqueous dispersion with a first crosslinking agent to provide
a gel;
(d) mixing the gel with a water-miscible solvent to provide composite fibers;
and
(e) treating the composite fibers with a second crosslinking agent to provide
mixed
polymer composite fibers. The mixed polymer composite fibers so prepared can
be
fiberized and dried.
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In the process, a carboxyalkyl cellulose, a galactomannan polymer or a
glucomannan polymer, and cellulose fibers are blended in water to provide an
aqueous
dispersion of cellulose in an aqueous polymer solution.
Suitable carboxyalkyl celluloses have a degree of carboxyl group substitution
of
from about 0.3 to about 2.5, and in one embodiment have a degree of carboxyl
group
substitution of from about 0.5 to about 1.5. In one embodiment, the
carboxyalkyl
cellulose is carboxymethyl cellulose. The aqueous dispersion includes from
about 60 to
about 99% by weight carboxyalkyl cellulose based on the weight of the product
mixed
polymer composite fiber. In one embodiment, the aqueous dispersion includes
from
about 80 to about 95% by weight carboxyalkyl cellulose based on the weight of
mixed
polymer composite fiber. Carboxyalkyl hemicellulose may also be present from
about
0 to about 20 percent by weight based on the weight of mixed polymer composite
fibers.
The aqueous dispersion also includes a galactomannan polymer or a glucomannan
polymer. Suitable galactomannan polymers include guar gum, locust bean gum and
tara
gum. Suitable glucomannan polymers include konjac gum. The galactomannan
polymer
or glucomannan polymer can be from natural sources or obtained from
genetically-modified plants. The aqueous dispersion includes from about 1 to
about 20%
by weight galactomannan polymer or glucomannan polymer based on the weight of
the
mixed polymer composite fiber, and in one embodiment, the aqueous dispersion
includes
from about 1 to about 15% by weight galactomannan polymer or glucomannan
polymer
based on the weight of mixed polymer composite fibers.
The aqueous dispersion also includes cellulose fibers, which are added to the
aqueous polymer solution. The aqueous dispersion includes from about 2 to
about 15%
by weight cellulose fibers based on the weight of the mixed polymer composite
fiber, and
in one embodiment, the aqueous dispersion includes from about 5 to about 10%
by
weight cellulose fibers based on the weight of mixed polymer composite fibers.
In the method, the aqueous dispersion including the carboxyalkyl cellulose,
galactomannan polymer or glucomannan polymer, and cellulose fibers is treated
with a
first crosslinking agent to provide a gel.
Suitable first crosslinking agents include crosslinking agents that are
reactive
towards hydroxyl groups and carboxyl groups. Representative crosslinking
agents
include metallic crosslinking agents, such as aluminum (III) compounds,
titanium (IV)
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compounds, bismuth (III) compounds, boron (III) compounds, and zirconium (IV)
compounds. The numerals in parentheses in the preceding list of metallic
crosslinking
agents refers to the valency of the metal.
Representative metallic crosslinking agents include aluminum sulfate; aluminum
hydroxide; dihydroxy aluminum acetate (stabilized with boric acid); other
aluminum salts
of carboxylic acids and inorganic acids; other aluminum complexes, such as
Ultrion 8186
from Nalco Company (aluminum chloride hydroxide); boric acid; sodium
metaborate;
ammonium zirconium carbonate; zirconium compounds containing inorganic ions or
organic ions or neutral ligands; bismuth ammonium citrate; other bismuth salts
of
carboxylic acids and inorganic acids; titanium (IV) compounds, such as
titanium (IV)
bis(triethylaminato) bis(isopropoxide) (commercially available from the Dupont
Company under the designation Tyzor TE); and other titanates with alkoxide or
carboxylate ligands.
The first crosslinking agent is effective for associating and crosslinking the
carboxyalkyl cellulose (with or without carboxyalkyl hemicellulose) and
galactomannan
polymer molecules intimately associated with the cellulose fibers. The first
crosslinking
agent is applied in an amount of from about 0.1 to about 20% by weight based
on the
total weight of the mixed polymer composite fiber. The amount of first
crosslinking
agent applied to the polymers will vary depending on the crosslinking agent.
In general,
the fibers have an aluminum content of about 0.04 to about 0.8% by weight
based on the
weight of the mixed polymer composite fiber for aluminum crosslinked fibers, a
titanium
content of about 0.10 to about 1.5% by weight based on the weight of the mixed
polymer
composite fiber for aluminum crosslinked fibers, a zirconium content of about
0.09 to
about 2.0% by weight based on the weight of the mixed polymer composite fiber
for
zirconium crosslinked fibers, and a bismuth content of about 0.90 to about
5.0% by
weight based on the weight of the mixed polymer composite fiber for bismuth
crosslinked
fibers.
The gel formed by treating the aqueous dispersion of cellulose fibers in the
aqueous solution of the carboxyalkyl cellulose and galactomannan polymer with
a first
crosslinking agent is then mixed with a water-miscible solvent to provide
composite
fibers. Suitable water-miscible solvents include water-miscible alcohols and
ketones.
Representative water-miscible solvents include acetone, methanol, ethanol,
isopropanol,
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and mixtures thereof. In one embodiment, the water-miscible solvent is
ethanol. In
another embodiment, the water-miscible solvent is isopropanol.
The volume of water-miscible solvent added to the gel ranges from about 1:1 to
about 1:5 water (the volume used in making the aqueous dispersion of
carboxyalkyl
cellulose, galactomannan polymer, and cellulose fibers) to water-miscible
solvent.
In the method, mixing the gel with the water-miscible solvent includes
stirring to
provide composite fibers. The mixing step and the use of the water-miscible
solvent
controls the rate of dehydration and solvent exchange under shear mixing
conditions and
provides for composite fiber formation. Mixing can be carried out using a
variety of
devices including overhead stirrers, Hobart mixers, British disintegrators,
and blenders.
For these mixing devices, the blender provides the greatest shear and the
overhead stirrer
provides the least shear. As noted above, fiber formation results from shear
mixing the
gel with the water-miscible solvent and effects solvent exchange and
generation of
composite fiber in the resultant mixed solvent.
In one embodiment, mixing the gel with a water-miscible solvent to provide
composite fibers comprises mixing a 1 or 2% solids in water with an overhead
mixer or
stirrer. In another embodiment, mixing the gel with a water-miscible solvent
to provide
composite fibers comprises mixing 4% solids in water with a blender. For large
scale
production alternative mixing equipment with suitable mixing capacities are
used.
Composite fibers formed from the mixing step are treated with a second
crosslinking agent to provide the mixed polymer composite fibers (crosslinked
fibers).
The second crosslinking agent is effective in further crosslinking (e.g.,
surface
crosslinking) the composite fibers. Suitable second crosslinking agents
include
crosslinking agents that are reactive towards hydroxyl groups and carboxyl
groups. The
second crosslinking agent can be the same as or different from the first
crosslinking
agent. Representative second crosslinking agents include the metallic
crosslinking agents
noted above useful as the first crosslinking agents.
The second crosslinking agent is applied at a relatively higher level than the
first
crosslinking agent per unit mass of fiber. This provides a higher degree of
crosslinking
on the surface of the fiber relative to the interior of the fiber. As
described above, metal
crosslinking agents form crosslinks between carboxylate anions and metal atoms
or
cellulose hydroxyl oxygen and metal atoms. These crosslinks can migrate from
one
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oxygen atom to another when the mixed polymer fiber absorbs water and forms a
gel.
However, having a higher level of crosslinks on the surface of the fiber
relative to the
interior provides a superabsorbent fiber with a suitable balance in free
swell, centrifuge
retention capacity, absorbency under load for aqueous solutions and lowers the
gel
blocking that inhibits liquid transport.
The second crosslinking agent is applied in an amount from about 0.1 to about
20% by weight based on the total weight of mixed polymer composite fibers. The
amount of second crosslinking agent applied to the polymers will vary
depending on the
crosslinking agent. The product fibers have an aluminum content of about 0.04
to about
2.0% by weight based on the weight of the mixed polymer composite fiber for
aluminum
crosslinked fibers, a titanium content of about 0.1 to about 4.5% by weight
based on the
weight of the mixed polymer composite fiber for titanium crosslinked fibers, a
zirconium
content of about 0.09 to about 6.0% by weight based on the weight of the mixed
polymer
composite fiber for zirconium crosslinked fibers, and a bismuth content of
about 0.09 to
about 5.0% by weight based on the weight of the mixed polymer composite fiber
for
bismuth crosslinked fibers.
The second crosslinking agent may be the same as or different from the first
crosslinking agent. Mixtures of two or more crosslinking agents in different
ratios may
be used in each crosslinking step.
The preparation of representative mixed polymer composite fibers of the
invention are described in Examples 1-4.
The absorbent properties of the representative mixed polymer composite fibers
are
summarized in the Table 1. In Table 1, "% wgt total wgt, applied" refers to
the amount of
first crosslinking agent applied to the total weight of CMC and guar gum;
"Second
crosslinking agent/2g" refers to the amount of second crosslinking agent
applied per 2 g
first crosslinked product; "CMC 9H4F" refers to a carboxymethyl cellulose
commercially
available from Hoechst Celanese under that designation; "KL-SW" refers to CMC
made
from northern softwood pulp; "LV-PN" refers to CMC made from west coast pine
pulp;
"NB416" refers to southern pine pulp fibers; and "PA Fluff" refers northern
softwood
pulp fibers; "i-PrOH" refers to isopropanol; "EtOH" refers to ethanol;"w wash"
refers to
washing the treated fibers with 100% ethanol or 100% isopropanol before
drying; and
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"wo washing" refers to the process in which the treated fibers are not washed
before
drying.
Test Methods
Free Swell and Centrifuge Retention Capacities
The materials, procedure, and calculations to determine free swell capacity
(g/g)
and centrifuge retention capacity (CRC) (g/g) were as follows.
Test Materials:
Japanese pre-made empty tea bags (available from Drugstore.com, IN PURSUIT
OF TEA polyester tea bags 93 mm x 70 mm with fold-over flap.
(http:www.mesh.ne.jp/tokiwa/)).
Balance (4 decimal place accuracy, 0.0001g for air-dried superabsorbent
polymer
(ADS SAP) and tea bag weights); timer; 1% saline; drip rack with clips (NLM
211); and
lab centrifuge (NLM 211, Spin-X spin extractor, model 776S, 3,300 RPM, 120v).
Test Procedure:
1. Determine solids content of ADS.
2. Pre-weigh tea bags to nearest 0.0001g and record.
3. Accurately weigh 0.2025g +/- 0.0025g of test material (SAP), record and
place
into pre-weighed tea bag (air-dried (AD) bag weight). (ADS weight + AD bag
weight =
total dry weight).
4. Fold tea bag edge over closing bag.
5. Fill a container (at least 3 inches deep) with at least 2 inches with 1 Io
saline.
6. Hold tea bag (with test sample) flat and shake to distribute test material
evenly
through bag.
7. Lay tea bag onto surface of saline and start timer.
8. Soak bags for specified time (e.g., 30 minutes).
9. Remove tea bags carefully, being careful not to spill any contents from
bags,
hang from a clip on drip rack for 3 minutes.
10. Carefully remove each bag, weigh, and record (drip weight).
11. Place tea bags onto centrifuge walls, being careful not to let them touch
and
careful to balance evenly around wall.
12. Lock down lid and start timer. Spin for 75 seconds.
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13. Unlock lid and remove bags. Weigh each bag and record weight (centrifuge
weight).
Calculations:
The tea bag material has an absorbency determined as follows:
Free Swell Capacity, factor = 5.78
Centrifuge Capacity, factor = 0.50
Z = Oven dry SAP wt (g)/Air dry SAP wt (g)
Free Capacity (g/g):
[(drip wt (g)- dry bag wt (g)) - (AD SAP wt (g))1- (drybagwt (g) * 5.78)
(AD SAP wt (g) * Z)
Centrifuge Retention Capacity (g/g):
[centrifuge wt (g) - dry bag wt (g) - (AD SAP wt (g))l - (dry bag wt(g)* 0.50)
(AD SAP wt * Z)
Absorbency Under Load (AUL)
The materials, procedure, and calculations to determine AUL were as follows.
Test Materials:
Mettler Toledo PB 3002 balance and BALANCE-LINK software or other
compatible balance and software. Software set-up: record weight from balance
every
sec _(this will be a negative number. Software can place each value into EXCEL
spreadsheet.
Kontes 90 mm ULTRA-WARE filter set up with fritted glass (coarse) filter
plate.
clamped to stand; 2 L glass bottle with outlet tube near bottom of bottle;
rubber stopper
25 with glass tube through the stopper that fits the bottle (air inlet); TYGON
tubing; stainless
steel rod/plexiglass plunger assembly (71mm diameter); stainless steel weight
with hole
drill through to place over plunger (plunger and weight = 867 g); VWR 9.0 cm
filter
papers (Qualitative 413 catalog number 28310-048) cut down to 80 mm size;
double-stick
SCOTCH tape; and 0.9% saline.
30 Test Procedure:
1. Level filter set-up with small level.
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CA 02603476 2007-09-20
2. Adjust filter height or fluid level in bottle so that fritted glass filter
and saline
level in bottle are at same height.
3. Make sure that there are no kinks in tubing or air bubbles in tubing or
under
fritted glass filter plate.
4. Place filter paper into filter and place stainless steel weight onto filter
paper.
5. Wait for 5-10 min while filter paper becomes fully wetted and reaches
equilibrium with applied weight.
6. Zero balance.
7. While waiting for filter paper to reach equilibrium prepare plunger with
double
stick tape on bottom.
8. Place plunger (with tape) onto separate scale and zero scale.
9. Place plunger into dry test material so that a monolayer of material is
stuck to
the bottom by the double stick tape.
10. Weigh the plunger and test material on zeroed scale and record weight of
dry
test material (dry material weight 0.15 g+/- 0.05 g).
11. Filter paper should be at equilibrium by now, zero scale.
12. Start balance recording software.
13. Remove weight and place plunger and test material into filter assembly.
14. Place weight onto plunger assembly.
15. Wait for test to complete (30 or 60 min)
16. Stop balance recording softw-are.
Calculations:
A = balance reading (g) *-1 (weight of saline absorbed by test material)
B = dry weight of test material (this can be corrected for moisture by
multiplying the AD weight by solids %).
AUL (g/g) = A/B (g 1% saline/lg test material)
The following examples are provided for the purpose of illustrating, not
limiting,
the invention.
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CA 02603476 2007-09-20
EXAMPLES
Example 1
The Preparation of Representative Mixed Polymer Composite Fibers:
Aluminum Sulfate/Aluminum Sulfate Crosslinking
In this example, the preparation of representative mixed polymer composite
fibers
crosslinked with aluminum sulfate and aluminum sulfate is described.
A solution of CMC 9H4F (20.0 g OD) in 900 ml deionized (DI) water was
prepared with vigorous stirring to obtain a solution. Guar gum (1.2 g) was
dissolved in
50 ml DI water and mix well with the CMC solution. Fluff pulp (1.0 g NB416)
was
added and the solution stirred for one hour to allow complete mixing of the
two polymers
and cellulose fiber.
The polymer mixture was blended in the blender for 5 minutes. Weigh
1.2 g aluminum sulfate octadecahydrate and dissolve in 50 ml DI water.
Transfer
aluminum sulfate solution to the polymer solution and blend for 5 minutes to
mix well.
Leave the gel at ambient temperature (25 C) for one hour. Transfer the gel
into a Waring
type blender with one liter of isopropanol. Mix for 1 minutes at low speed
(gave a softer
gel). Transfer the gel to a 5 gallon plastic bucket. Add two liters of
isopropanol and mix
rapidly with the vertical spiral mixer for 30 minutes. Filter and place the
fiber in 500 ml
of isopropanol and leave for 15 minutes. Filter the fiber and dry in an oven
at 66 C for
15-30 minutes.
_ Dissolve 0.32 g of aluminum sulfate octadecahydrate in 100ml of deionized
water and mix with 300 ml of denatured ethanol. To the stirred solution add
2.0 g of
fiber, prepared as described above, and leave for 30 minutes at 25 C. Filter
the fiber and
press excess solution out. Filter and dry the product fiber at 66 C for 15
minutes in an
oven with fluffing. Free swell (60.6 g/g), centrifuge retention capacity
(30.98 g/g), for
0.9% saline solution.
Example 2
The Preparation of Representative Mixed Polymer Composite Fibers:
Aluminum Sulfate/Aluminum Sulfate Crosslinking
In this example, the preparation of representative mixed polymer composite
fibers
crosslinked with aluminum sulfate and aluminum sulfate is described.
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CA 02603476 2007-09-20
A solution of CMC 9H4F (40.0 g OD) and 2.4 g guar gum in 900 ml deionized
water was prepared in a Hobart mixer to obtain a viscous polymer solution in 2
hours.
Initially mix at speed one and increase speed to two and finally to three.
Fluff pulp
(4.0 g PA) in 50 ml water was added and mixed at speed three for one hour.
Dissolve 1.2 g aluminum sulfate octadecahydrate in 50 ml DI water. Transfer
the
crosslinker solution to the polymer solution and mix well in the Hobart mixer
(initially at
speed one and then gradually increasing the speed to three as the crosslinker
solution
becomes absorbed into the gel (one hour)). Transfer the gel into a Waring type
blender
with one liter of isopropanol. Mix for 2 minutes at low speed (gave a softer
gel). Add
two liters of isopropanol and blend at low speed and powerstat setting of 70
for one
minute. Filter and place the fiber in one liter of isopropanol and in the
blender and blend
at low power and powerstat setting of 70 for one minute. Filter the fiber and
dry in an
oven at 66 C for 15-30 minutes.
Dissolve 0.20 g of aluminum sulfate octadecahydrate in 100 ml of deionized
water and mix with 300 ml of isopropanol. To the stirred solution add 2.0 g of
fiber,
prepared as described above, and leave for 15 minutes at 25 C. Filter the
fiber and press
excess solution out. Filter and dry the fiber at 66 C for 15 minutes in an
oven with
fluffing. Free swell (52.04 g/g), centrifuge retention capacity (21.83 g/g),
AUL at 0.3 psi
(23.73 g/g) for 0.9% saline solution.
Example 3
The Preparation of ReTresentative Mixed Polymer Composite FiUers,
Aluminum Sulfate/Aluminum Sulfate Crosslinking
In this example, the preparation of representative mixed polymer composite
fibers
crosslinked with aluminum sulfate and aluminum sulfate is described.
A solution of Kamloops softwood (DS = 0.94) CMC (20.0 g OD) in 900 ml
deionized water was prepared with vigorous stirring to obtain a solution. Guar
gum
(1.2 g) was dissolved in 50 ml DI water and mixed well with the CMC solution.
Fluff
pulp (2.0 g NB416) was added and the mixture stirred for one hour to allow
complete
mixing of the two polymers and cellulose fiber.
The mixture was blended in the blender for 5 minutes. Weigh 0.8 g aluminum
sulfate octadecahydrate and dissolve in 50 ml DI water. Transfer aluminum
sulfate
solution to the polymer solution and blend for 5 minutes to mix well. Leave
the gel at
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CA 02603476 2007-09-20
ambient temperature (25 C) for one hour. Transfer the gel into a Waring type
blender
with one liter of denatured ethanol. Mix for 2 minutes at low speed (gave a
softer gel),
then add 2 liters of ethanol and blend at low power and power stat setting of
70 for one
minute. Filter and place the fiber in 500 ml of ethanol and stir for 15
minutes. Filter the
fiber and dry in an oven at 66 C for 15 minutes.
Dissolve 0.28 g of aluminum sulfate octadecahydrate in 50 ml of deionized
water
and mix with 150 ml of denatured ethanol. To the stirred solution add 2.0 g of
fiber,
prepared as described above, and leave for 30 minutes at 25 C. Filter the
fiber and press
excess solution out. Filter and dry the fiber at 66 C for 15 minutes in an
oven with
fluffing. Free swell (57.61 g/g), centrifuge retention capacity (25.45 g/g),
AUL at 0.3 psi
(22.26 g/g) for 0.9% saline solution.
Example 4
The Preparation of Representative Mixed Polymer Composite Fibers:
Aluminum Sulfate/Aluminum Sulfate Crosslinking
In this example, the preparation of representative mixed polymer composite
fibers
crosslinked with aluminum sulfate and aluminum sulfate is described.
A solution of Longview pine (DS = 0.98) CMC (40.0 g OD) and 2.4 g guar gum
in 900 ml deionized water was prepared with gradual increase in mixing speed
in a
Hobart mixer. Fluff pulp (4.0 g NB416) in 50 ml DI water was added and mixed
to allow
complete mixing of the two polymers and cellulose fiber.
Dissolve 1.2 g aluminum sulfate octadecahydrate in 50 ml DI water. Transfer
aluminum sulfate solution to the polymer mixture and mix well. Leave the gel
at ambient
temperature (25 C) for one hour. Transfer the gel into a Waring type blender
with one
liter of isopropanol. Mix for 2 minutes at low speed and 90 power stat setting
(gave a
softer gel), and then add 2 liters of isopropanol and blend at low power and
power stat
setting of 60 for one minute. Filter and place the fiber in one liter of
isopropanol and stir
for 15 minutes. Filter the fiber and dry in an oven at 66 C for 15 minutes.
Screen out
small fraction below 300 micrometer size.
Dissolve 0.22 g of aluminum sulfate octadecahydrate in 50 ml of deionized
water
and mix with 150 ml of isopropanol. To the stirred solution add 2.0 g of
fiber, prepared
as described above, and leave for 40 minutes at 25 C. Filter the fiber and
press excess
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CA 02603476 2007-09-20
solution out. Filter and air dry the fiber at 25 C. Free swell (56.77 g/g),
centrifuge
retention capacity (28.95 g/g), AUL at 0.3 psi (22.66 g/g) for 0.9% saline
solution.
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CA 02603476 2007-09-20
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-20
CA 02603476 2007-09-20
While illustrative embodiments have been illustrated and described, it will be
appreciated that various changes can be made therein without departing from
the spirit
and scope of the invention.
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