U.S. patent application number 11/610353 was filed with the patent office on 2008-04-03 for mixed polymer superabsorbent fibers and method for their preparation.
This patent application is currently assigned to Weyerhaeuser Co.. Invention is credited to Mengkui Luo, S. Ananda Weerawarna.
Application Number | 20080081189 11/610353 |
Document ID | / |
Family ID | 39153776 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080081189 |
Kind Code |
A1 |
Weerawarna; S. Ananda ; et
al. |
April 3, 2008 |
Mixed Polymer Superabsorbent Fibers And Method For Their
Preparation
Abstract
A method for making mixed polymer composite fibers in which a
carboxyalkyl cellulose and a galactomannan polymer or a glucomannan
polymer are blended in water to provide an aqueous solution; the
aqueous solution treated with a first crosslinking agent to provide
a gel; the gel is formed into get fibers using melt blowing,
centrifugal spinning, wet spinning or dry-jet wet spinning; and the
fibers treated with water miscible solvent to form mixed polymer
composite fibers. The fiber has a diameter in the range of 50 .mu.m
to 1000 .mu.m.
Inventors: |
Weerawarna; S. Ananda;
(Seattle, WA) ; Luo; Mengkui; (Auburn,
WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY;INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
Weyerhaeuser Co.
Federal Way
WA
|
Family ID: |
39153776 |
Appl. No.: |
11/610353 |
Filed: |
December 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11537849 |
Oct 2, 2006 |
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11610353 |
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11537989 |
Oct 2, 2006 |
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11537849 |
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Current U.S.
Class: |
428/364 |
Current CPC
Class: |
A61L 15/60 20130101;
Y10T 428/2913 20150115 |
Class at
Publication: |
428/364 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Claims
1. A method for making mixed polymer composite fibers, comprising:
(a) blending a carboxyalkyl cellulose and a galactomannan polymer
or glucomannan polymer in water to provide an aqueous solution; (b)
treating the aqueous solution with a first crosslinking agent to
provide a gel; (c) forming gel fibers from the get using melt
blowing, centrifugal spinning, wet spinning, or dry-jet wet
spinning, (d) treating the gel fibers with a water-miscible solvent
to provide mixed polymer composite fibers.
2. The method of claim 1 wherein in step (d) the gel fibers are
treated in a solvent bath.
3. The method of claim 1 wherein in step (d) the gel fibers are
treated by a solvent spray.
4. The method of claim 1 further comprising drying the fiberized
fibers to provide dried crosslinked mixed polymer composite
fibers.
5. The method of claim 1, wherein the carboxyalkyl cellulose has a
degree of carboxyl group substitution of from about 0.3 to about
2.5.
6. The method of claim 1, wherein the carboxyalkyl cellulose is
carboxymethyl cellulose.
7. The method of claim 1, wherein the galactomannan polymer is
selected from the group consisting of guar gum, locust bean gum,
tara gum, and fenugreek gum.
8. The method of claim 1, wherein the glucomannan polymer is konjac
gum.
9. The method of claim 1, wherein the aqueous solution comprises
from about 60 to about 99 percent by weight carboxyalkyl cellulose
based on the total weight of mixed polymer composite fibers.
11. The method of claim 1, wherein the aqueous solution comprises
from about 1 to about 20 percent by weight galactomannan or
glucomannan polymer based on the total weight of mixed polymer
composite fibers.
12. The method of claim 1, wherein the first crosslinking agent is
a carboxyl group crosslinking agent.
13. The method of claim 1, wherein the first crosslinking agent is
a hydroxyl group crosslinking agent.
14. The method of claim 1, wherein the first crosslinking agent is
selected from the group consisting of aluminum (III) compounds,
titanium (IV) compounds, bismuth (III) compounds, boron (III)
compounds, and zirconium (IV) compounds.
15. The method of claim 1, wherein the first crosslinking agent is
applied in an amount from about 0.1 to about 20 percent by weight
based on the total weight of mixed polymer composite fibers.
16. The method of claim 1, wherein the water-miscible solvent is an
alcohol.
17. The method of claim 1, wherein the water-miscible solvent is
selected from the group consisting of methanol, ethanol,
isopropanol, and mixtures thereof.
18. The method of claim 1 further comprising treating the gel
fibers with a second crosslinking agent during step (d).
19. The method of claim 18, wherein the second crosslinking agent
is selected from the group consisting of aluminum (III) compounds,
titanium (IV) compounds, bismuth (III) compounds, boron (III)
compounds, and zirconium (IV) compounds.
20. The method of claim 18, wherein the second crosslinking agent
is applied in an amount from about 0.1 to about 20 percent by
weight based on the total weight of crosslinked fibers.
21. A mixed polymer composite fiber, comprising a carboxyalkyl
cellulose and a galactomannan polymer or a glucomannan polymer,
having a diameter in the range of 50 .mu.m to 1000 .mu.m.
Description
RELATIONSHIP TO OTHER APPLICATIONS
[0001] This application is a continuation-in-part of application
Ser. No. 11/537,849, Methods for the preparation of mixed polymer
superabsorbent fibers, and application Ser. No. 11/537,989, Mixed
polymer superabsorbent fibers, both filed Oct. 2, 2006, and.
BACKGROUND OF THE INVENTION
[0002] 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 state. When there is a lot
of interstitial liquid the "rewet" value or "wet feeling" of an
absorbent product is compromised.
[0003] 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.
[0004] 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.
[0005] 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
[0006] The present invention provides a method for making mixed
polymer composite fibers. In the method, a carboxyalkyl cellulose
and a galactomannan polymer or glucomannan polymer are blended in
water to provide an aqueous solution; the aqueous solution treated
with a first crosslinking agent to provide a gel.
[0007] In one embodiment the get is then spun into gel fibers using
centrifugal spinning. In another embodiment the gel is extruded
into gel fibers using meltblowing. In another embodiment the gel is
formed into gel fibers using wet spinning.
[0008] In an embodiment the spun or extruded gel fibers are
precipitated into solid fibers by being passed into a solvent bath
to provide mixed polymer composite fibers. In another embodiment
the spun or extruded gel fibers are precipitated into solid fibers
by being sprayed with a solvent to provide mixed polymer composite
fibers. The solvent bath or spray uses a water miscible
solvent.
[0009] In another embodiment the bath or spray may contain a second
crosslinking agent to provide further crosslinking of the
fibers.
[0010] The mixed polymer composite fibers may then be dried.
[0011] The method allows fibers of a specific and predetermined
diameter and cross-section to be formed. The fibers may have
diameter of 50 .mu.m to 1000 .mu.m. In some instances the diameter
of the fibers may vary along the fiber length.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram of a dry-jet wet process.
[0013] FIG. 2 is a diagram of a centrifugal spinning process.
[0014] FIG. 3 is a diagram of a meltblow spinning process.
[0015] FIG. 4 is a diagram of a meltblow head for the meltblow
spinning process.
[0016] FIG. 5 is a diagram of a wet spinning process.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides a method for making mixed
polymer composite fibers. In the method, a carboxyalkyl cellulose
and a galactomannan polymer or glucomannan polymer are blended in
water to provide an aqueous solution; the aqueous solution treated
with a first crosslinking agent to provide a gel; the gel is then
spun or extruded into fibers using centrifuge spinning, meltblowing
or wet spinning methods. The spun or extruded fibers pass into a
solvent bath to provide formed fibers. The solvent is a
water-miscible solvent/water mixture. The bath may contain a second
crosslinking agent to provide further crosslinking of the
fibers.
[0018] The mixed polymer composite fiber is a fiber comprising a
carboxyalkyl cellulose and a galactomannan polymer or glucomannan
polymer. 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.
[0019] As used herein, the term "mixed polymer composite fiber"
refers to a fiber that is the composite of two different water
soluble polymers (i.e., mixed polymers). The mixed polymer
composite fiber is a homogeneous composition that includes two
associated polymers: (1) a carboxyalkyl cellulose and (2) either a
galactomannan polymer or a glucomannan polymer.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] The galactomannan polymer useful in making the mixed polymer
composite fiber 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 tar gum.
In another embodiment, the galactomannan polymer is fenugreek
gum.
[0024] The glucomannan polymer useful in making the mixed polymer
composite fiber can include any one of a variety of glucomannan
polymers. In one embodiment, the glucomannan polymer is konjac
gum.
[0025] 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 polymer is present in an
amount from about 1 to about 15% by weight based on the weight of
the mixed polymer composite fiber. In a further embodiment, the
galactomannan polymer or glucomannan polymer is present in an
amount from about 2 to about 15% by weight based on the weight of
the mixed polymer composite fiber.
[0026] 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. Then, a first crosslinking agent is added and mixed to
obtain a mixed polymer composite gel formed by intermolecular
crosslinking of water-soluble polymers.
[0027] 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.
[0028] In one embodiment the gel is formed into fibers through the
use of a dry-jet wet spinning process. A diagram of the dry jet wet
spinning process is shown in FIG. 1. The gel is pumped through a
transfer line 1 through a spinning block 2, through the orifices of
spinneret 3 through a layer of gas or air 5 and into a bath 6 where
the fibers 4 are conducted by guides 7 and 8 and precipitated into
mixed polymer composite fiber 15 which is wound up on a take-up
roll 9.
[0029] In another embodiment the gel is formed into fibers through
the use of centrifugal spinning. FIG. 2 is a diagram of centrifugal
spinning. In centrifugal spinning the gel 20 is directed in a
generally hollow cylinder or drum 21 with a closed base and a
multiplicity of small apertures 22 in its sidewalls 23. As the
cylinder rotates, the gel is forced out horizontally through the
apertures as thin gel strands or gel fibers 24. As the strands meet
resistance from the surrounding air they are drawn or stretched.
The amount of stretch will depend on readily controllable factors
such as cylinder rotational speed, orifice size of the apertures
and the viscosity of the gel. The strands either fall by gravity or
are forced down by air flow into a water miscible solvent 25 held
in a basin 26 where the gel fibers are precipitated into mixed
polymer composite fibers. Alternatively, the fibers 24 may be
sprayed with a water-miscible solvent from a ring of spray nozzles
27 fed by line 28.
[0030] In another embodiment the gel is formed into fibers through
the use of melt blowing technology. FIGS. 3 and 4 are diagrams of
melt blowing. In melt blowing the gel is directed to an extruder 32
which forces the gel through an orifice head 34 having a
multiplicity of orifices 36. Air or another gas is supplied through
lines 38 and surrounds and transports extruded gel fibers 40. The
air or gas moves in parallel with the fibers and impinges on the
fibers, transporting the fibers, and drawing and stretching the
fibers. The gel fibers move into the bath 42 which contains a
water-miscible solvent 44 which precipitates the gel fibers to form
mixed polymer composite fibers. As in centrifugal spinning the gel
fibers may be sprayed with the water-miscible solvent to form the
mixed polymer composite fibers instead of being placed in a bath.
Below orifice 36 and above bath 42, solvent circulated from bath 42
can be sprayed onto fibers 40 too.
[0031] FIG. 4 shows a typical extrusion orifice. The orifice plate
50 is bored with a multiplicity of orifices 36. The plate 50 is
held to the body of the extrusion head 51 by a series of cap screws
52. An internal member 53 forms the extrusion ports 54 for the gel.
It is embraced by air passages 55 that surround the extruded gel
fibers 40 causing them to be drawn and to assist in their transport
to the bath. The amount the gel fibers are drawn or stretched will
depend on the viscosity of the gel, the speed of the fiber travel
and the gas travel, and the angle between the gas and the fiber.
Depending on the speed and angle of the fiber and gas, long
continuous fibers may be formed or short fibers may be formed.
[0032] In another embodiment the gel may be formed into fibers by
wet spinning. A diagram of wet spinning is shown in FIG. 5. In wet
spinning the gel is passed by a pump 60 through pipe 61 leading
into bath 62 containing the water-miscible solvent 63. The gel is
extruded through spinneret 64 directly into the bath to form mixed
polymer composite fibers 65 which are guided from by the transfer
roll 66 to a take up roll. The amount of time of the gel in the
bath will depend on the speed of the fibers and the placement of
the spinneret in the bath. A short retention time is shown. A
different placement of the spinneret will increase the retention
time in the bath. The fibers are fixed in the bath. Alternatively,
fiber 65 can be collected on a moving screen.
[0033] The mixed polymer composite fiber thus obtained may be
further crosslinked (e.g., surface crosslinked) by treating with a
second crosslinking agent in the treating bath or spray. The second
crosslinking agent can be the same as or different from the first
crosslinking agent. The need for a second crosslinking step will
depend on the amount of crosslinking that has been generated in the
initial crosslinking. If the initial crosslinking is light then the
fiber generated after first crosslinking has a high level of
sliminess when hydrated and forms soft gels and cannot be used in
absorbent applications without further treatment. If the
crosslinking in the first or initial crosslinking is greater the
fiber generated after the first crosslinking will not be slimy and
will be a hard gel.
[0034] The mixed polymer fibers are substantially insoluble in
water while being capable of absorbing water. The fibers 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 fiber
(i.e., intra-fiber) and among and between each fiber's constituent
polymer molecules.
[0035] The fibers are intra-fiber crosslinked with metal
crosslinks. The metal crosslinks arise as a consequence of an
associative interaction (e.g., bonding) between functional groups
(e.g., carboxy, carboxylate, or hydroxyl groups) of the fiber's
polymers 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 associative interpolymer
interactions with functional groups of the polymer molecules (e.g.,
reactive toward associative interaction with the carboxy,
carboxylate, or hydroxyl groups). The polymers are crosslinked when
the multi-valent metal species form associative interpolymer
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.
[0036] The fibers include non-permanent intrafiber 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 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 gel was 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 dissociate
and re-associate.
[0037] The fibers have fiber widths of from about 2 .mu.m to about
100 .mu.m and coarseness that varies from soft to rough. Melt blown
fibers have diameters that vary along the length of the fiber to
give an undulating cross section to the fiber.
[0038] The fibers are highly absorptive fibers. The fibers can have
a Free Swell Capacity of from about 25 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).
[0039] The fibers 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 can
absorb liquid at a rate of from about 10 ml/sec to about 0.005
ml/sec (0.9% saline solution/10 ml application). The integrity of
the pads can be varied from soft to very strong.
[0040] The mixed polymer composite fibers 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 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 advantageously has dual
properties of high liquid absorbent capacity and liquid wicking
capacity.
[0041] 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.
[0042] The mixed polymer composite fibers 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 are useful in a variety of other
applications, including, for example, wound dressings, cable wrap,
absorbent sheets or bags, and packaging materials.
[0043] In one aspect of the invention, methods for making mixed
polymer composite fibers are provided. In the methods, the mixed
polymer composite fibers are formed by spinning or extruding the
gel into a fiber and then precipitating the fiber to form a mixed
polymer composite fiber by a water-miscible solvent bath or
spray.
[0044] In one embodiment, the method for making the mixed polymer
composite fibers (crosslinked fibers) includes the steps of: (a)
blending a carboxyalkyl cellulose (e.g., mainly salt form) and a
galactomannan polymer or a glucomannan polymer in water to provide
an aqueous solution; (b) treating the aqueous solution with a first
crosslinking agent to provide a gel; (c) forming a fiber from the
gel by centrifugal spinning; and (d) treating the gel fiber in a
water-miscible solvent bath or by water-miscible solvent spray to
provide to precipitate the mixed polymer composite fibers.
[0045] In another embodiment, the method for making the mixed
polymer composite fibers (crosslinked fibers) includes the steps
of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form)
and a galactomannan polymer or a glucomannan polymer in water to
provide an aqueous solution; (b) treating the aqueous solution with
a first crosslinking agent to provide a gel; (c) forming a fiber
from the gel by melt blowing; and (d) treating the gel fiber in a
water-miscible solvent bath or by water-miscible solvent spray to
provide mixed polymer composite fibers.
[0046] In another embodiment, the method for making the mixed
polymer composite fibers (crosslinked fibers) includes the steps
of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form)
and a galactomannan polymer or a glucomannan polymer in water to
provide an aqueous solution; (b) treating the aqueous solution with
a first crosslinking agent to provide a gel; (c) forming a fiber
from the gel by wet spinning; and (d) treating the gel fiber in a
water-miscible solvent bath to provide mixed polymer composite
fibers.
[0047] In another embodiment, the method for making the mixed
polymer composite fibers (crosslinked fibers) includes the steps
of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form)
and a galactomannan polymer or a glucomannan polymer in water to
provide an aqueous solution; (b) treating the aqueous solution with
a first crosslinking agent to provide a gel; (c) forming a fiber
from the gel by jet-dry wet spinning; and (d) treating the gel
fiber in a water-miscible solvent bath to provide mixed polymer
composite fibers.
[0048] In another embodiment step (d) in each of the above methods
may include treating the fibers with a second crosslinking agent
(e.g., surface crosslinking) by having the second crosslinking
agent in the bath or spray to provide mixed polymer composite
fibers.
[0049] The fibers may have a diameter of 50 .mu.m to 1000 .mu.m.
Melt blown fibers may be nonuniform in diameter along the fiber
length.
[0050] The mixed polymer composite fibers so prepared can be
dried.
[0051] The fibers may have a diameter of 50 .mu.m to 1000
.mu.m.
[0052] In the process, a carboxyalkyl cellulose and a galactomannan
polymer or a glucomannan polymer are blended in water to provide an
aqueous solution.
[0053] 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 solution 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 solution includes from about 80 to about
95% by weight carboxyalkyl cellulose based on the weight of mixed
polymer composite fiber.
[0054] Suitable galactomannan polymers include guar gum, locust
bean gum, tara gum, and fenugreek 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 solution includes from
about 1 to about 20% by weight galactomannan polymer or glucomannan
polymer based on the weight of the mixed polymer composite fibers,
and in one embodiment, the aqueous solution includes from about 1
to about 15% by weight galactomannan polymer or glucomannan polymer
based on the weight of mixed polymer composite fibers.
[0055] In the method, the aqueous solution including the
carboxyalkyl cellulose and galactomannan polymer or glucomannan
polymer is treated with a suitable amount of a first crosslinking
agent to provide a gel.
[0056] 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 (II) 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.
[0057] 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.
[0058] The first crosslinking agent is effective for associating
and crosslinking the carboxyalkyl cellulose (with or without
carboxyalkyl hemicellulose) and galactomannan polymer molecules.
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 titanium 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.
[0059] The gel formed by treating the aqueous solution of a
carboxyalkyl cellulose and a galactomannan polymer with a first
crosslinking agent is then spun or extruded into a gel fiber by
centrifugal spinning, meltblowing or wet spinning.
[0060] The spun or extruded gel fibers are then precipitated to
form mixed polymer composite fibers by treatment by a
water-miscible solvent in either a bath or spray.
[0061] Suitable water-miscible solvents include water-miscible
alcohols and ketones. Representative water-miscible solvents
include acetone, methanol, ethanol, isopropanol, and mixtures
thereof. In one embodiment, the water-miscible solvent is ethanol.
In another embodiment, the water-miscible solvent is
isopropanol.
[0062] If the fibers formed from the spinning or extrusion step are
treated in a mixture of water and a water miscible solvent, the
proportions of water and solvent must be such that the fibers do
not lose their fiber form and form a gel.
[0063] A second crosslinking agent may be used in the bath or
spray. The second crosslinking agent is effective in further
crosslinking (e.g., surface crosslinking) the mixed polymer
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.
[0064] The second crosslinking agent can be 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 hydroxyl oxygen and metal
atoms. These crosslinks can migrate from one 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.
[0065] 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 1.0 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.
[0066] 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.
[0067] The resultant fibers, either with one crosslinking agent or
surface crosslinked with a second crosslinking agent, are then
washed with a water-miscible solvent and air dried or oven dried
below 80.degree. C. to provide the mixed polymer composite
fibers.
[0068] The preparation of representative mixed polymer composite
fibers are described in Examples 1-2.
Test Methods
Free Swell and Centrifuge Retention Capacities
[0069] The materials, procedure, and calculations to determine free
swell capacity (g/g) and centrifuge retention capacity (CRC) (gig)
were as follows.
[0070] Test Materials:
[0071] Japanese pre-made empty tea bags (available from
Drugstore.com, IN PURSUIT OF TEA polyester tea bags 93 mm.times.70
mm with fold-over flap. (http:www.mesh.ne.jp/tokiwa/)).
[0072] Balance (4 decimal place accuracy, 0.0001 g 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, 120 v).
[0073] Test Procedure:
[0074] 1. Determine solids content of ADS.
[0075] 2. Pre-weigh tea bags to nearest 0.0001 g and record.
[0076] 3. Accurately weigh 0.2025 g.+-.0.0025 g 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).
[0077] 4. Fold tea bag edge over closing bag.
[0078] 5. Fill a container (at least 3 inches deep) with at least 2
inches with 1% saline.
[0079] 6. Hold tea bag (with test sample) flat and shake to
distribute test material evenly through bag.
[0080] 7. Lay tea bag onto surface of saline and start timer.
[0081] 8. Soak bags for specified time (e.g., 30 minutes).
[0082] 9. Remove tea bags carefully, being careful not to spill any
contents from bags, hang from a clip on drip rack for 3
minutes.
[0083] 10. Carefully remove each bag, weigh, and record (drip
weight).
[0084] 11. Place tea bags onto centrifuge walls, being careful not
to let them touch and careful to balance evenly around wall.
[0085] 12. Lock down lid and start timer. Spin for 75 seconds.
[0086] 13. Unlock lid and remove bags. Weigh each bag and record
weight (centrifuge weight).
[0087] Calculations:
[0088] 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)
[0089] Free Capacity (g/g):
[ ( drip wt ( g ) - dry bag wt ( g ) ) - ( AD SAP wt ( g ) ) ] - (
dry bag wt ( g ) * 5.78 ) ( AD SAP wt ( g ) * Z ) ##EQU00001##
[0090] Centrifuge Retention Capacity (g/g):
[ centrifuge wt ( g ) - dry bag wt ( g ) - ( AD SAP wt ( g ) ) ] -
( dry bag wt ( g ) * 0.50 ) ( AD SAP wt * Z ) ##EQU00002##
Absorbency Under Load (AUL)
[0091] The materials, procedure, and calculations to determine AUL
were as follows.
[0092] Test Materials;
[0093] Mettler Toledo PB 3002 balance and BALANCE-LINK software or
other compatible balance and software. Software set-up: record
weight from balance every 30 sec (this will be a negative number.
Software can place each value into EXCEL spreadsheet.
[0094] 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 with glass tube
through the stopper that fits the bottle (air inlet); TYGON tubing;
stainless steel rod/plexiglass plunger assembly (71 mm 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.
[0095] Test Procedure:
[0096] 1. Level filter set-up with small level.
[0097] 2. Adjust filter height or fluid level in bottle so that
fritted glass filter and saline level in bottle are at same
height.
[0098] 3. Make sure that there are no kinks in tubing or air
bubbles in tubing or under fritted glass filter plate.
[0099] 4. Place filter paper into filter and place stainless steel
weight onto filter paper.
[0100] 5. Wait for 5-10 min while filter paper becomes fully wetted
and reaches equilibrium with applied weight.
[0101] 6. Zero balance.
[0102] 7. While waiting for filter paper to reach equilibrium
prepare plunger with double stick tape on bottom.
[0103] 8. Place plunger (with tape) onto separate scale and zero
scale.
[0104] 9. Place plunger into dry test material so that a monolayer
of material is stuck to the bottom by the double stick tape.
[0105] 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).
[0106] 11. Filter paper should be at equilibrium by now, zero
scale.
[0107] 12. Start balance recording software.
[0108] 13. Remove weight and place plunger and test material into
filter assembly.
[0109] 14. Place weight onto plunger assembly.
[0110] 15. Wait for test to complete (30 or 60 min)
[0111] 16. Stop balance recording software.
[0112] 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/1 g test material)
EXAMPLES
[0113] The following examples are provided for the purpose of
illustrating, not limiting, the invention. In the following
examples a laboratory extruder was used. It has a cylinder for the
material being extruded and a motor driven piston for extruding the
material at a controlled rate. The piston delivers the material
through a spin pack with a spinneret having a selected diameter.
The diameter of the spinneret can be changed. In the present
examples the spinneret discharged directly into a bath.
Example 1
[0114] A solution of CMC 9H4F 10.0 g OD in 450 ml deionized (DI)
water was prepared with vigorous stirring to obtain a CMC solution.
Guar gum (0.6 g) was dissolved in 25 ml DI water and mix well with
the CMC solution. The solution was stirred for one hour to allow
complete mixing of the two polymers.
[0115] The polymer mixture was blended in the blender. Fully
dissolve basic dihydroxy aluminum acetate stabilized with boric
acid (purchased from Sigma-Aldrich Fine Chemicals) 0.125 g in 25 ml
DI water. Transfer the aluminum acetate stabilized with boric acid
solution to the polymer solution and blend for five minutes to mix
to provide a gel. Leave the gel at ambient temperature (25.degree.
C.) for one hour.
Example 2
[0116] A solution of CMC 9H4F 10.0 g OD in 950 ml deionized (DI)
water was prepared with vigorous stirring to obtain a CMC solution.
Guar gum (0.6 g) was dissolved in 25 ml DI water and mix well with
the CMC solution. The solution was stirred for one hour to allow
complete mixing of the two polymers.
[0117] The polymer mixture was blended in the blender. Fully
dissolve basic dihydroxy aluminum acetate stabilized with boric
acid (purchased from Sigma-Aldrich Fine Chemicals) 0.125 g in 25 ml
DI water. Transfer the aluminum acetate stabilized with boric acid
solution to the polymer solution and blend for five minutes to
provide a gel. Leave the gel at ambient temperature (25.degree. C.)
for one hour.
Example 3
[0118] The aqueous gels described above in Examples 1 and 2 were
extruded in a wet spinning extruder to form a gel fiber. The gel
from the Example 1 was a 2% by weight solution and the gel from
Example 2 a 1% by weight solution. The get fiber was placed in a
denatured ethanol solvent to precipitate the fibers. There was no
second crosslinking. The filaments formed were 700 .mu.m in
diameter. The following table gives the amount of gel in solution
and the free swell, centrifuge capacity and AUL of the fibers. Free
swell, centrifuge capacity and AUL are in grams absorbed per gram
of fiber.
TABLE-US-00001 TABLE 1 gel in centrifuge Example solution, % Free
swell capacity AUL 1 2 31.2 13.32 18.71 1 2 27.16 14.03 22.95 2 1
34.51 17.07 13.23
Example 4
[0119] In this example, the preparation of representative mixed
polymer composite fibers crosslinked with fresh aluminum sulfate
and fresh aluminum sulfate is described. A solution of Weyerhaeuser
pine pulp CMC (40 g OD) in 900 ml deionized water was prepared with
vigorous stirring to obtain a CMC solution. Guar gum (2.4 g) was
dissolved in 50 ml DI water and mixed with the CMC solution. The
solution was stirred for one hour to allow complete mixing of the
two polymers.
[0120] Weigh 0.8 g of fresh 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.degree. C.) for one hour.
[0121] The gel was formed into fibers using wet spinning (one
orifice with hole diameter of 500 micron).
[0122] The gel fibers entered a water-miscible solvent bath
containing 1200 ml water and 3600 ml isopropanol containing a
second crosslinker. The crosslinker concentration in the following
table is based on the amount of crosslinker per 4 g dry gel
extruded. The second crosslinker was also fresh aluminum sulfate.
Each portion of precipitated fiber was then soaked in 500 ml of
isopropanol and mixed for 10 minutes. The fibers were then
dried.
[0123] The following table gives the speed of the gel through the
orifice, the amount of crosslinker in the bath, and the free swell,
and centrifuge capacity of the composite fiber. Free swell,
centrifuge capacity and AUL are in grams absorbed per gram of
fiber.
TABLE-US-00002 TABLE 2 gel rate. centrifuge g/min crosslinker %
free swell capacity 30 0.05 35.4 18.54 30 0.072 41.09 25.16 30
0.084 40.83 26.71 30 0.148 29.3 13.69 10 0.2 38.79 21.15
[0124] 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.
* * * * *