U.S. patent application number 09/860095 was filed with the patent office on 2002-02-07 for multicomponent superabsorbent fibers.
This patent application is currently assigned to BASF Aktiengesellschaft. Invention is credited to Evans, Samantha J., Henderson, John A., Mitchell, Michael A., Tomlin, Anthony S..
Application Number | 20020015846 09/860095 |
Document ID | / |
Family ID | 23045796 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015846 |
Kind Code |
A1 |
Evans, Samantha J. ; et
al. |
February 7, 2002 |
Multicomponent superabsorbent fibers
Abstract
Multicomponent superabsorbent fibers are disclosed. The
multicomponent fibers comprise at least one acidic water-absorbing
resin and at least one basic water-absorbing resin. Each fiber
contains at least one microdomain of the acidic resin in contact
with, or in close proximity to, at least one microdomain of the
basic resin. Blends of multicomponent superabsorbent fibers with
particles of a second water-absorbing resin also are disclosed.
Articles containing the multicomponent superabsorbent fibers also
are disclosed.
Inventors: |
Evans, Samantha J.; (Lymm
Cheshire, WA) ; Henderson, John A.; (Birkenhead,
GB) ; Mitchell, Michael A.; (Lake Zurich, IL)
; Tomlin, Anthony S.; (Island Lake, IL) |
Correspondence
Address: |
MARSHALL, O'TOOLE, GERSTEIN, MURRAY & BORUN
6300 SEARS TOWER
233 SOUTH WACKER DRIVE
CHICAGO
IL
60606-6402
US
|
Assignee: |
BASF Aktiengesellschaft
|
Family ID: |
23045796 |
Appl. No.: |
09/860095 |
Filed: |
May 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09860095 |
May 17, 2001 |
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09273878 |
Mar 22, 1999 |
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09273878 |
Mar 22, 1999 |
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09179553 |
Oct 28, 1998 |
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6222091 |
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09179553 |
Oct 28, 1998 |
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09120674 |
Jul 22, 1998 |
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6235965 |
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09120674 |
Jul 22, 1998 |
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08974125 |
Nov 19, 1997 |
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6072101 |
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Current U.S.
Class: |
428/373 |
Current CPC
Class: |
Y10T 428/2929 20150115;
C08L 101/14 20130101; A61F 13/53 20130101; Y10T 428/2931 20150115;
A61L 15/60 20130101; A61F 2013/530613 20130101; B01J 20/26
20130101; Y10T 428/2924 20150115; D01F 8/10 20130101 |
Class at
Publication: |
428/373 |
International
Class: |
D02G 003/00 |
Claims
What is claimed is:
1. A multicomponent superabsorbent fiber comprising: (a) a core
comprising at least one basic water-absorbing resin and (b) a
sheath comprising at least one acidic water-absorbing resin which
forms a layer surrounding and in contact with the core.
2. The fiber of claim 1 wherein the basic resin comprises a strong
basic resin, a weak basic resin, or a mixture thereof, and the
acidic resin comprises a strong acidic resin, a weak acidic resin,
or a mixture thereof.
3. The fiber of claim 1 having a weight ratio of acidic resin to
basic resin of about 95:5 to about 5:95.
4. The fiber of claim 1 wherein the core contains at least one
microdomain of at least one acidic resin.
5. The fiber of claim 1 wherein the sheath contains at least one
microdomain of at least one basic resin.
6. The fiber of claim 1 wherein the fiber is elongated and
acicular.
7. The fiber of claim 6 wherein the fiber is in the shape of a
cylinder having a diameter of about 10 .mu.m to about 1 mm and a
length of about 1 mm to about 100 mm.
8. The fiber of claim 6 wherein the fiber is in the shape of a
filament having a length diameter ratio of about 500 to about
10,000:1.
9. The fiber of claim 1 wherein the fiber is annealed at a
temperature of about 65.degree. C. to about 150.degree. C. for
about 20 minutes to about 16 hours.
10. The fiber of claim 1 wherein the fiber is surface crosslinked
with up to about 10,000 ppm of a surface crosslinking agent.
11. The fiber of claim 10 wherein the surface crosslinking agent is
selected from the group consisting of a polyhydroxy compound, a
metal salt, a quaternary ammonium compound, a multifunctional epoxy
compound, an alkylene carbonate, a polyaziridine, a haloepoxy, a
polyamine, a polyisocyanate, and mixtures thereof.
12. The fiber of claim 1 wherein the basic resin has about 75% to
100% basic moieties present in a free base form.
13. The fiber of claim 1 wherein the basic resin is lightly
crosslinked.
14. The fiber of claim 1 wherein the basic resin is selected from
the group consisting of a poly(vinylamine), a
poly(dialkylaminoalkyl (meth)acrylamide), a polymer prepared from
the ester analog of an N-(dialkylamino(meth)acrylamide), a
polyethylenimine, a poly(vinylguanidine), a poly(allylguanidine), a
poly(allylamine), a poly(dimethyldialkylammonium hydroxide), a
guanidine-modified polystyrene, a quaternized polystyrene, a
quaternized poly(meth)acrylamide or ester analog thereof,
poly(vinyl alcohol-co-vinylamine), and mixtures thereof.
15. The fiber of claim 1 wherein the acidic resin contains a
plurality of carboxylic acid, sulfonic acid, sulfuric acid,
phosphonic acid, or phosphoric acid groups, or a mixture
thereof.
16. The fiber of claim 1 wherein the acidic resin has about 75% to
100% acid moieties present in the free acid form.
17. The fiber of claim 1 wherein the acidic resin is lightly
crosslinked.
18. The fiber of claim 1 wherein the acidic resin is selected from
the group consisting of polyacrylic acid, a hydrolyzed
starch-acrylonitrile graft copolymer, a starch-acrylic acid graft
copolymer, a saponified vinyl acetate-acrylic ester copolymer, a
hydrolyzed acrylonitrile polymer, a hydrolyzed acrylamide
copolymer, an ethylene-maleic anhydride copolymer, an
isobutylene-maleic anhydride copolymer, a poly(vinylphosphonic
acid), a poly(vinylsulfonic acid), a poly(vinylphosphoric acid), a
poly(vinyl-sulfuric acid), a sulfonated polystyrene, a
poly(aspartic acid), a poly(lactic acid), and mixtures thereof.
19. The fiber of claim 1 wherein the basic resin comprises a
poly(vinylamine), a poly(dialkylaminoalkyl (meth)acrylamide), a
poly(vinylguanidine), a polyethylenimine, or a mixture thereof, and
the acidic resin comprises poly(acrylic acid).
20. The fiber of claim 19 wherein the poly(dialkylaminoalkyl
(meth)acrylamide) comprises poly(dimethylaminoethyl acrylamide),
poly(dimethylaminopropyl methacrylamide), or a mixture thereof.
21. The fiber of claim 19 wherein the poly(acrylic acid) resin
further contains strong acid moieties.
22. The fiber of claim 1 wherein the core has voids.
23. An article comprising a core containing a superabsorbent
polymer, said core comprising about 1% to 100% by weight of a
multicomponent superabsorbent fiber of claim 1.
24. A method of absorbing an aqueous medium comprising contacting
the medium with a plurality of fibers of claim 1.
25. A method of claim 24 wherein the aqueous medium contains
electrolytes.
26. A method of claim 25 wherein the electrolyte-containing aqueous
medium is selected from the group consisting of urine, saline,
menses, and blood.
27. A superabsorbent material comprising: (a) multicomponent
superabsorbent fibers of claim 1, and (b) particles of a second
water-absorbing resin selected from the group consisting of an
acidic water-absorbing resin, a basic water-absorbing resin, and
mixtures thereof.
28. The superabsorbent material of claim 27 wherein the
multicomponent superabsorbent fibers are present in an amount of
about 10% to about 90%, by weight, of the material.
29. The superabsorbent material of claim 27 wherein the
multicomponent superabsorbent fibers are 0% to 25% neutralized, and
the second water-absorbing resin is 0% to 100% neutralized.
30. The superabsorbent material of claim 27 wherein the second
water-absorbing resin comprises an acidic water-absorbing
resin.
31. A multicomponent superabsorbent fiber comprising: (a) a core
comprising at least one acidic water-absorbing resin and (b) a
sheath comprising at least one basic water-absorbing resin which
forms a layer surrounding and in contact with the core.
32. The fiber of claim 31 wherein the fiber is surface crosslinked
with up to about 10,000 ppm of a surface crosslinking agent.
33. The fiber of claim 32 wherein the surface crosslinking agent is
selected from the group consisting of (a) a dihalide or a
disulfonate ester having the formula Y--(CH.sub.2).sub.p--Y,wherein
p is an integer 2 to 12 and Y, independently, is halo, tosylate,
mesylate, an alkyl sulfonate ester, or an aryl sulfonate ester; (b)
a multifunctional aziridine; (c) a multifunctional aldehyde, and
acetals and bisulfites thereof; (d) a halohydrin; (e) a
multifunctional epoxy compound; (f) a multifunctional carboxylic
acid containing 2 to 12 carbon atoms, and methyl and ethyl esters,
acid chlorides, and anhydrides derived therefrom; (g) an organic
titanate; (h) a melamine resin; (i) a hydroxymethyl urea; (j) a
multifunctional isocyanate; and (k) mixtures thereof.
34. The fiber of claim 31 wherein the particle is annealed at a
temperature of about 65.degree. C. to about 150.degree. C. for
about 20 minutes to about 16 hours.
35. The fiber of claim 31 wherein the core contains at least one
microdomain of at least one basic resin.
36. The fiber of claim 31 wherein the sheath contains at least one
microdomain of at least one acidic resin.
37. An article comprising a multicomponent superabsorbent fiber of
claim 31.
38. A method of absorbing an aqueous medium comprising contacting
the medium with a plurality of fibers of claim 31.
39. A superabsorbent material comprising: (a) multicomponent
superabsorbent fibers of claim 31, and (b) particles of a second
water-absorbing resin selected from the group consisting of an
acidic water-absorbing resin, a basic water-absorbing resin, and
mixtures thereof.
40. The superabsorbent material of claim 39 wherein the
multicomponent superabsorbent fibers are 0% to 25% neutralized, and
the second water-absorbing resin is 0% to 100% neutralized.
41. The superabsorbent material of claim 39 wherein the second
water-absorbing resin comprises an acidic water-absorbing
resin.
42. A multicomponent superabsorbent fiber comprising: (a) one or
more first fibers comprising an acidic resin, and (b) one or more
second fibers comprising a basic resin, wherein the first and
second fibers are twisted together in the form of a braid.
43. The fiber of claim 42 wherein the first fiber contains at least
one microdomain of at least one basic resin.
44. The fiber of claim 42 wherein the second fiber contains at
least one microdomain of at least one acidic resin.
45. The fiber of claim 42 wherein the fiber is annealed at a
temperature of about 65.degree. C. to about 150.degree. C. for
about 20 minutes to about 16 hours.
46. The fiber of claim 42 wherein the first fiber, the second
fiber, both the first and second fibers are surface crosslinked
with up to about 10,000 ppm of a surface crosslinking agent.
47. The fiber of claim 42 wherein the fiber is surface crosslinked
with up to about 10,000 ppm of a surface crosslinking agent.
48. An article comprising a core containing a superabsorbent
polymer, said core comprising about 1% to 100% by weight of a
multicomponent superabsorbent fiber of claim 42.
49. A method of absorbing an aqueous medium comprising contacting
the medium with a plurality of fibers of claim 42.
50. The method of claim 49 wherein the aqueous medium contains
electroytes.
51. A multicomponent superabsorbent fiber comprising: (a) a
plurality of first fibers comprising an acidic resin, and (b) a
plurality of second fibers comprising a basic resin, wherein the
first and second fibers are admixed, then formed into the shape of
a mat.
52. The fiber of claim 51 wherein the mat is annealed at a
temperature of about 65.degree. C. to about 150.degree. C. for
about 20 minutes to about 160 hours.
53. The fiber of claim 51 wherein the mat retains its structural
integrity after hydration with a liquid medium.
54. An article comprising a core containing about 1% to 100% by
weight of a multicomponent superabsorbent fiber of claim 51.
55. A method of manufacturing a multicomponent superabsorbent fiber
comprising a core comprising a poly(vinylamine) surrounded by a
sheath comprising a poly(acrylic acid), said method comprising: (a)
forming an aqueous solution comprising an uncrosslinked
poly(vinylamine) and about 0.001 mol % to about 0.1 mol % of a
crosslinking agent, (b) heating the aqueous solution of step (a) to
lightly crosslink the uncrosslinked polyvinylamine and form a
spinning dope, (c) introducing the spinning dope of step (b) into a
coagulation bath containing about 0.1% to about 2% by weight of a
crosslinking agent dissolved in a nonsolvent for poly(vinylamine)
to form a filament of crosslinked poly(vinylamine), (d) directing
the crosslinked poly(vinylamine) filament of step (c) from the
coagulation bath to a bath comprising poly(acrylic acid), about 0.5
to about 5% by weight of a crosslinking agent, and a solvent, (e)
passing the crosslinked poly(vinylamine) through the bath of step
(d) to form a sheath of poly(acrylic acid) over the crosslinked
poly(vinylamine) filament, (f) directing the filament from step (e)
to a doping bath containing a curing catalyst, and (g) curing the
filament from step (f) to provide the multicomponent superabsorbent
fiber.
56. The method of claim 55 wherein the crosslinked poly(vinylamine)
dried after step (c) and prior to step (d).
57. The method of claim 55 wherein the filament formed in step (e)
is dried prior to step (f).
58. The method of claim 55 wherein the crosslinking agent in step
(a) comprising ethylene glycol diglycidyl ether.
59. The method of claim 55 wherein the crosslinking agent in step
(c) comprising ethylene glycol diglycidyl ether.
60. The method of claim 55 wherein the crosslinking agent in step
(d) comprising ethylene glycol diglycidyl ether.
61. The method of claim 55 wherein the curing catalyst of step (f)
comprises triethylamine.
62. The method of claim 55 wherein the filament of step (f) is
cured in step (g) by heating for about 10 to about 60 minutes at
about 60.degree. C. to about 150.degree. C.
63. A method of manufacturing a multicomponent superabsorbent
comprising a mixed bed of fibers of an acidic resin and fibers of a
basic resin, said method comprising: (a) admixing a plurality of
acidic resin fibers and a plurality of basic resin fibers to form a
fiber mixture; (b) forming the fiber mixture into a mixed bed of a
predetermined shape and thickness; and (c) annealing the mixed bed
at a temperature of about 65.degree. C. to about 150.degree. C. for
about 20 minutes to about 16 hours.
64. The method of claim 63 wherein the fiber mixture is formed into
the shape of a diaper core.
65. The fiber of claim 1 wherein the fiber retains its structural
integrity after hydration with a liquid medium.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part application of U.S. patent
application Ser. No. 09/179,553, filed Oct. 28, 1998, pending,
which is a continuation-in-part of U.S. patent application Ser. No.
09/120,674, filed Jul. 22, 1998, pending, which is a
continuation-in-part of U.S. patent application Ser. No.
08/974,125, filed Nov. 19, 1997, pending.
FIELD OF THE INVENTION
[0002] The present invention relates to multicomponent
superabsorbent particles, in fiber form, containing at least one
acidic water-absorbing resin and at least one basic water-absorbing
resin. Each multicomponent superabsorbent fiber has at least one
microdomain of the acidic resin in contact with, or in close
proximity to, at least one microdomain of the basic resin. The
present invention also relates to mixtures containing (a)
multicomponent superabsorbent fibers, and (b) particles of an
acidic water-absorbing resin, a basic water-absorbing resin, or a
mixture thereof.
BACKGROUND OF THE INVENTION
[0003] Water-absorbing resins are widely used in sanitary goods,
hygienic goods, wiping cloths, water-retaining agents, dehydrating
agents, sludge coagulants, disposable towels and bath mats,
disposable door mats, thickening agents, disposable litter mats for
pets, condensation-preventing agents, and release control agents
for various chemicals. Water-absorbing resins are available in a
variety of chemical forms, including substituted and unsubstituted
natural and synthetic polymers, such as hydrolysis products of
starch acrylonitrile graft polymers, carboxymethylcellulose,
crosslinked polyacrylates, sulfonated polystyrenes, hydrolyzed
polyacrylamides, polyvinyl alcohols, polyethylene oxides,
polyvinylpyrrolidones, and polyacrylonitriles.
[0004] Such water-absorbing resins are termed "superabsorbent
polymers," or SAPs, and typically are lightly crosslinked
hydrophilic polymers. SAPs are generally discussed in Goldman et
al. U.S. Pat. Nos. 5,669,894 and 5,559,335, the disclosures of
which are incorporated herein by reference. SAPs can differ in
their chemical identity, but all SAPs are capable of absorbing and
retaining amounts of aqueous fluids equivalent to many times their
own weight, even under moderate pressure. For example, SAPs can
absorb one hundred times their own weight, or more, of distilled
water. The ability to absorb aqueous fluids under a confining
pressure is an important requirement for an SAP used in a hygienic
article, such as a diaper.
[0005] As used here and hereafter, the term "SAP particles" refers
to superabsorbent polymer particles in the dry state, i.e.,
particles containing from no water up to an amount of water less
than the weight of the particles. The terms "SAP gel" or "SAP
hydrogel" refer to a superabsorbent polymer in the hydrated state,
i.e., particles that have absorbed at least their weight in water,
and typically several times their weight in water. The SAP
particles disclosed herein are in fiber form.
[0006] The dramatic swelling and absorbent properties of SAPs are
attributed to (a) electrostatic repulsion between the charges along
the polymer chains, and (b) osmotic pressure of the counter ions.
It is known, however, that these absorption properties are
drastically reduced in solutions containing electrolytes, such as
saline, urine, and blood. The polymers function much less
effectively in the presence of such physiologic fluids.
[0007] The decreased absorbency of electrolyte-containing liquids
is illustrated by the absorption properties of a typical,
commercially available SAP, i.e., sodium polyacrylate, in deionized
water and in 0.9% by weight sodium chloride (NaCl) solution. The
sodium polyacrylate can absorb 146.2 grams (g) of deionized water
per gram of SAP (g/g) at 0 psi, 103.8 g of deionized water per gram
of polymer at 0.28 psi, and 34.3 g of deionized water per gram of
polymer of 0.7 psi. In contrast, the same sodium polyacrylate is
capable of absorbing only 43.5 g, 29.7 g, and 24.8 g of 0.9%
aqueous NaCl at 0 psi, 0.28 psi, and 0.7 psi, respectively. The
absorption capacity of SAPs for body fluids, such as urine or
menses, therefore, is dramatically lower than for deionized water
because such fluids contain electrolytes. This dramatic decrease in
absorption is termed "salt poisoning."
[0008] The salt poisoning effect has been explained as follows.
Water-absorption and water-retention characteristics of SAPs are
attributed to the presence of ionizable functional groups in the
polymer structure. The ionizable groups typically are carboxyl
groups, a high proportion of which are in the salt form when the
polymer is dry, and which undergo dissociation and salvation upon
contact with water. In the dissociated state, the polymer chain
contains a plurality of functional groups having the same electric
charge and, thus, repel one another. This electronic repulsion
leads to expansion of the polymer structure, which, in turn,
permits further absorption of water molecules. Polymer expansion,
however, is limited by the crosslinks in the polymer structure,
which are present in a sufficient number to prevent solubilization
of the polymer.
[0009] It is theorized that the presence of a significant
concentration of electrolytes interferes with dissociation of the
ionizable functional groups, and leads to the "salt poisoning"
effect. Dissolved ions, such as sodium and chloride ions,
therefore, have two effects on SAP gels. The ions screen the
polymer charges and the ions eliminate the osmotic imbalance due to
the presence of counter ions inside and outside of the gel. The
dissolved ions, therefore, effectively convert an ionic gel into a
nonionic gel, and swelling properties are lost.
[0010] The most commonly used SAP for absorbing
electrolyte-containing liquids, such as urine, is neutralized
polyacrylic acid, i.e., containing at least 50%, and up to 100%,
neutralized carboxyl groups. Neutralized polyacrylic acid, however,
is susceptible to salt poisoning. Therefore, to provide an SAP that
is less susceptible to salt poisoning, either an SAP different from
neutralized polyacrylic acid must be developed, or the neutralized
polyacrylic acid must be modified or treated to at least partially
overcome the salt poisoning effect.
[0011] The removal of ions from electrolyte-containing solutions is
often accomplished using ion exchange resins. In this process,
deionization is performed by contacting an electrolyte-containing
solution with two different types of ion exchange resins, i.e., an
anion exchange resin and a cation exchange resin. The most common
deionization procedure uses an acidic resin (i.e., cation exchange)
and a basic resin (i.e., anion exchange). The two-step reaction for
deionization is illustrated with respect to the desalinization of
water as follows:
NaCl+R--SO.sub.3H.fwdarw.R--SO.sub.3Na+HCl
HCl+R--N(CH.sub.3).sub.3OH.fwda-
rw.R--N(CH.sub.3).sub.3Cl+H.sub.2O.
[0012] The acidic resin (R--SO.sub.3H) removes the sodium ion; and
the basic resin (R--N(CH.sub.3).sub.3OH) removes the chloride ions.
This ion exchange reaction, therefore, produces water as sodium
chloride is adsorbed onto the resins. The resins used in ion
exchange do not absorb significant amounts of water.
[0013] The most efficient ion exchange occurs when strong acid and
strong base resins are employed. However, weak acid and weak base
resins also can be used to deionize saline solutions. The
efficiency of various combinations of acid and base exchange resins
are as follows:
[0014] Strong acid--strong base (most efficient)
[0015] Weak acid--strong base
[0016] Strong acid--weak base
[0017] Weak acid--weak base (least efficient).
[0018] The weak acid/weak base resin combination requires that a
"mixed bed" configuration be used to obtain deionization. The
strong acid/strong base resin combination does not necessarily
require a mixed bed configuration to deionize water. Deionization
also can be achieved by sequentially passing the
electrolyte-containing solution through a strong acid resin and
strong base resin.
[0019] A "mixed bed" configuration of the prior art is a physical
mixture of an acid ion exchange resin and a base ion exchange resin
in an ion exchange column, as disclosed in Battaerd U.S. Pat. No.
3,716,481. Other patents directed to ion exchange resins having one
ion exchange resin imbedded in a second ion exchange resin are
Hatch U.S. Pat. No. 3,957,698, Wade et al. U.S. Pat. No. 4,139,499,
Eppinger et al. U.S. Pat. No. 4,229,545, and Pilkington U.S. Pat.
No. 4,378,439. Composite ion exchange resins also are disclosed in
Hatch U.S. Pat. Nos. 3,041,092 and 3,332,890, and Weiss U.S. Pat.
No. 3,645,922.
[0020] The above patents are directed to nonswelling resins that
can be used to remove ions from aqueous fluids, and thereby provide
purified water. Ion exchange resins used for water purification
must not absorb significant amounts of water because resin swelling
resulting from absorption can lead to bursting of the ion exchange
containment column.
[0021] Ion exchange resins or fibers also have been disclosed for
use in absorbent personal care devices (e.g., diapers) to control
the pH of fluids that reach the skin, as set forth in Berg et al.,
U.S. Pat. No. 4,685,909. The ion exchange resin is used in this
application to reduce diaper rash, but the ion exchange resin is
not significantly water absorbent and, therefore, does not improve
the absorption and retention properties of the diaper.
[0022] Ion exchange resins having a composite particle containing
acid and base ion exchange particles embedded together in a matrix
resin, or having acid and base ion exchange particles adjacent to
one another in a particle that is free of a matrix resin are
disclosed in B. A. Bolto et al., J. Polymer Sci.:Symposium No. 55,
John Wiley and Sons, Inc. (1976), pages 87-94. The Bolto et al.
publication is directed to improving the reaction rates of ion
exchange resins for water purification and does not utilize resins
that absorb substantial amounts of water.
[0023] Other investigators have attempted to counteract the salt
poisoning effect and thereby improve the performance of SAPs with
respect to absorbing electrolyte-containing liquids, such as menses
and urine. For example, Tanaka et al. U.S. Pat. No. 5,274,018
discloses an SAP composition comprising a swellable hydrophilic
polymer, such as polyacrylic acid, and an amount of an ionizable
surfactant sufficient to form at least a monolayer of surfactant on
the polymer. In another embodiment, a cationic gel, such as a gel
containing quaternized ammonium groups and in the hydroxide (i.e.,
OH) form, is admixed with an anionic gel (i.e., a polyacrylic acid)
to remove electrolytes from the solution by ion exchange.
Quaternized ammonium groups in the hydroxide form are very
difficult and time-consuming to manufacture, thereby limiting the
practical use of such cationic gels.
[0024] Wong U.S. Pat. No. 4,818,598 discloses the addition of a
fibrous anion exchange material, such as DEAE (diethylaminoethyl)
cellulose, to a hydrogel, such as a polyacrylate, to improve
absorption properties. The ion exchange resin "pretreats" the
saline solution (e.g., urine) as the solution flows through an
absorbent structure (e.g., a diaper). This pretreatment removes a
portion of the salt from the saline. The conventional SAP present
in the absorbent structure then absorbs the treated saline more
efficiently than untreated saline. The ion exchange resin, per se,
does not absorb the saline solution, but merely helps overcome the
"salt poisoning" effect.
[0025] WO 96/17681 discloses admixing discrete anionic SAP
particles, such as polyacrylic acid, with discrete
polysaccharide-based cationic SAP particles to overcome the salt
poisoning effect. Similarly, WO 96/15163 discloses combining a
cationic SAP having at least 20% of the functional groups in a
basic (i.e., OH) form with a cationic exchange resin, i.e., a
nonswelling ion exchange resin, having at least 50% of the
functional groups in the acid form. WO 96/15180 discloses an
absorbent material comprising an anionic SAP, e.g., a polyacrylic
acid and an anion exchange resin, i.e., a nonswelling ion exchange
resin.
[0026] SAP particles in fiber form are known. For example, Allen
U.S. Pat. No. 5,147,956 and Allen et al. U.S. Pat. Nos. 4,962,172;
4,861,539; and 4,280,079 disclose absorbent products and their
method of manufacture. Farrar et al. U.S. Pat. No. 4,997,714 also
discloses absorbent products in a fiber form, and their method of
manufacture. Additional patents include Morgan U.S. Pat. No.
3,867,499, Funk U.S. Pat. No. 4,913,869, and Tai et al. U.S. Pat.
No. 5,667,743. GB 2,269,602 discloses a wet-laid nonwoven fabric
comprising a blend of SAP fibers and a less absorbing fiber, like
woodpulp. European Patent Application 0 425 269 discloses a melt
spun fiber containing a conventional synthetic material and an SAP.
WO 98/24832 discloses an absorbent composition containing an acidic
and basic material. The absorbent composition can be in a fiber
form. Further patents directed to fibers include WO 96/JP651, WO
97/43480, and Hills U.S. Pat. No. 5,162,074.
[0027] Various references disclose combinations that attempt to
overcome the salt poisoning effect. However, the references do not
teach SAP fibers having the improved fluid absorption and retention
properties, or absorption kinetics, demonstrated by the fibers of
the present invention, which comprise at least one microdomain of
an acidic resin in contact, or in close proximity, with at least
one microdomain of a basic resin. These references also do not
teach a mixture of resin particles wherein one component of the
mixture is fibers of a multicomponent SAP.
[0028] The present invention, therefore, is directed to discrete
SAP fibers that exhibit exceptional water absorption and retention
properties, especially with respect to electrolyte-containing
liquids, and thereby overcome the salt poisoning effect. In
addition, the discrete SAP fibers have an ability to absorb liquids
quickly, demonstrate good fluid permeability and conductivity into
and through the SAP fiber, and have a high gel strength such that
the hydrogel formed from the SAP fibers does not deform or flow
under an applied stress or pressure, when used alone or in a
mixture with other water-absorbing resins.
SUMMARY OF THE INVENTION
[0029] The present invention is directed to multicomponent SAPs, in
fiber form, comprising at least one acidic water-absorbing resin,
such as a polyacrylic acid, and at least one basic water-absorbing
resin, such as a poly(vinylamine), a polyethyleneimine, or a
poly(dialkylaminoalkyl acrylamide) or a poly(dialkylaminoalkyl
methacrylamide), hereafter collectively referred to as
poly(dialkylaminoalkyl(meth)acrylamides).
[0030] More particularly, the present invention is directed to
multicomponent SAP fibers containing at least one discrete
microdomain of at least one acidic water-absorbing resin in contact
with, or in close proximity to, at least one microdomain of at
least one basic water-absorbing resin. The acidic resin can be a
strong or a weak acidic resin. Similarly, the basic resin can be a
strong or a weak basic resin.
[0031] A preferred SAP contains one or more microdomains of at
least one weak acidic resin and one or more microdomains of at
least one weak basic resin. The properties demonstrated by such
preferred multicomponent SAP particles are unexpected because, in
ion exchange applications, the combination of a weak acid and a
weak base is the least effective of any combination of a strong or
weak acid ion exchange resin with a strong or weak basic ion
exchange resin.
[0032] The multicomponent SAP fibers can contain a plurality of
microdomains of the acidic water-absorbing resin and/or the basic
water-absorbing resin dispersed throughout the particle.
Alternatively, the multicomponent SAP fibers can be in the form of
a core and sheath, wherein the core is a microdomain of a first
water-absorbing resin and the sheath is a microdomain of a second
water-absorbing resin. The multicomponent SAP fibers also can be in
the form of a fiber of an acidic water-absorbing resin and a fiber
of a basic water-absorbing resin that are twisted together in the
form of a braid or rope.
[0033] Accordingly, one aspect of the present invention is to
provide SAP fibers that have a high absorption rate, have good
permeability and gel strength, overcome the salt poisoning effect,
and demonstrate an improved ability to absorb and retain
electrolyte-containing liquids, such as saline, blood, urine, and
menses. The present SAP fibers contain discrete microdomains of
acidic and basic resin, and during hydration, the fibers resist
coalescence but remain fluid permeable.
[0034] Another aspect of the present invention is to provide an SAP
having improved absorption and retention properties compared to a
conventional SAP, such as sodium polyacrylate. The present
multicomponent SAP fibers are produced by any method that positions
a microdomain of an acidic water-absorbing resin in contact with,
or in close proximity to, a microdomain of a basic water-absorbing
resin to provide a discrete particle. Such SAP particles
demonstrate improved absorption and retention properties, and
permeability through and between particles compared to SAP
compositions comprising a simple admixture of acidic resin
particles and basic resin particles.
[0035] In one embodiment, the SAP fibers are produced by
coextruding an acidic water-absorbing hydrogel and a basic
water-absorbing hydrogel to provide multicomponent SAP fibers
having a plurality of discrete microdomains of an acidic resin and
a basic resin dispersed throughout the particle. In another
embodiment, the present multicomponent SAP fibers can be prepared
by admixing dry particles of a basic resin with a hydrogel of an
acidic resin, then extruding the resulting mixture to form
multicomponent SAP fibers having microdomains of a basic resin
dispersed throughout a continuous phase of an acidic resin.
Alternatively, dry acidic resin particles can be admixed with a
basic resin hydrogel, followed by extruding the resulting mixture
to form multicomponent SAP fibers having microdomains of an acidic
resin dispersed in a continuous phase of a basic resin.
[0036] In addition, a multicomponent SAP fiber containing
microdomains of an acidic resin and a basic resin dispersed in a
continuous phase of a matrix resin can be prepared by adding dry
particles of the acidic resin and dry particles of the basic resin
to a hydrogel of the matrix hydrogel, then extruding.
[0037] In other embodiments, the acidic and basic water-absorbing
hydrogels are coextruded, or spun, to form a fiber having a
core-sheath configuration. Alternatively, the acidic and basic
water-absorbing hydrogels are extruded, or spun, individually, then
twisted together, in the form of a braid, to provide a
multicomponent SAP fiber.
[0038] In accordance with yet another important aspect of the
present invention, the acidic and basic resins are lightly
crosslinked, such as with a suitable polyfunctional vinyl polymer.
In preferred embodiments, the acidic resin, the basic resin, and/or
the entire multicomponent SAP fiber are surface treated or annealed
to further improve water absorption and retention properties,
especially under a load.
[0039] Yet another important feature of the present invention is to
provide an SAP fiber containing at least one microdomain of a weak
acidic water-absorbing resin in contact with at least one
microdomain of a weak basic water-absorbing resin.
[0040] An example of a weak acidic resin is polyacrylic acid having
0% to 25% neutralized carboxylic acid groups (i.e., DN=0 to DN=25).
Examples of weak basic water-absorbing resins are a
poly(vinylamine), a polyethylenimine, and a poly(dialkylaminoalkyl
(meth)acrylamide) prepared from a monomer either having the general
structure formula (I) 1
[0041] or the ester analog of (I) having the general structure
formula (II) 2
[0042] wherein R.sub.1 and R.sub.2, independently, are selected
from the group consisting of hydrogen and methyl, Y is a divalent
straight chain or branched organic radical having 1 to 8 carbon
atoms, and R.sub.3 and R.sub.4, independently, are alkyl radicals
having 1 to 4 carbon atoms. Examples of a strong basic
water-absorbing resin are poly(vinylguanidine) and
poly(allylguanidine).
[0043] Yet another aspect of the present invention is to provide an
improved SAP material comprising a combination containing (a)
multicomponent SAP fibers, and (b) particles of a second
water-absorbing resin selected from the group consisting of an
acidic water-absorbing resin, a basic water-absorbing resin, and a
mixture thereof. The combination contains about 10% to about 90%,
by weight, multicomponent SAP fibers and about 10% to about 90%, by
weight, particles of the second water-absorbing resin.
[0044] Another important aspect of the present invention is to
provide a method of continuously producing core-sheath
multicomponent SAP fibers. In one embodiment, a poly(vinylamine)
core is prepared using a wet spinning method, which then is
immediately directed to a solution containing poly(acrylic acid)
and a crosslinker. The freshly spun poly(vinylamine) fiber,
therefore, has a sheath of poly(acrylic acid) applied thereto.
[0045] Still another aspect of the present invention is to provide
diapers having a core comprising multicomponent SAP fibers or an
SAP material of the present invention. Other articles that can
contain the multicomponent SAP fibers or an SAP material of the
present invention include catamenial devices, adult incontinence
products, and devices for absorbing saline and other ion-containing
fluids.
[0046] These and other aspects and advantages of the present
invention will become apparent from the following detailed
description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a cross-sectional view of a water-absorbing fiber
containing microdomains of a first resin dispersed in a continuous
phase of a second resin;
[0048] FIG. 2 is a cross-sectional view of a water-absorbing
particle containing microdomains of a first resin and microdomains
of a second resin dispersed throughout the particle;
[0049] FIGS. 3A and 3B are cross-sectional views of a
water-absorbing fiber having a core microdomain of a first resin
surrounded by a sheath microdomain of a second resin;
[0050] FIGS. 4A and 4B are cross-sectional views of water-absorbing
fibers having a microdomain of a first resin in contact with a
microdomain of a second resin;
[0051] FIGS. 5A and 5B are schematic diagrams of a water-absorbing
fiber having individual fibers of a first and a second
water-absorbing resin twisted together to form a rope;
[0052] FIG. 6 contains plots of absorbance (in grams of synthetic
urine per gram of multicomponent SAP granules) vs. annealing
temperature for a one-hour annealing step;
[0053] FIG. 7 contains a plot of absorbance (in grams of synthetic
urine per gram of multicomponent SAP granules) vs. time for an
annealing step performed at 125.degree. C.;
[0054] FIG. 8 is a schematic illustration of a dry spinning
apparatus;
[0055] FIG. 9 is a schematic illustration of a wet spinning
apparatus;
[0056] FIG. 10 contains plots of AUL (0.28 psi) (g/g) vs. time for
rate of absorption of twisted SAP fibers cured at 125.degree. C.
for 20 mins.; and
[0057] FIGS. 11 and 12 are scanning electron micrographs of the
multicomponent SAP fibers of Example 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] The present invention is directed to multicomponent SAP
particles, in fiber form, containing at least one microdomain of an
acidic water-absorbing resin in close proximity to, and preferably
in contact with, at least one microdomain of a basic
water-absorbing resin. Each fiber particle contains one or more
microdomains of an acidic resin and one or more microdomains of a
basic resin. The microdomains can be distributed nonhomogeneously
or homogeneously throughout each fiber particle.
[0059] Each multicomponent SAP fiber of the present invention
contains at least one acidic water-absorbing resin and at least one
basic water-absorbing resin. In one embodiment, the SAP fibers
consist essentially of acidic resins and basic resins, and contain
microdomains of the acidic and/or basic resins. In another
embodiment, microdomains of the acidic and basic resins are
dispersed in an absorbent matrix resin.
[0060] The multicomponent SAP particles of the present invention
are in the shape of a fiber. It is important that substantially
each SAP particle contain at least one microdomain of an acidic
water-absorbing resin and at least one microdomain of a basic
water-absorbing resin in close proximity to one another. Improved
water absorption and retention, and improved fluid permeability
through and between SAP particles, are observed as long as the
acidic resin microdomain and the basic resin microdomain are in
close proximity within the particle. In a preferred embodiment, the
microdomains of acidic and basic resin are in contact.
[0061] In some embodiments, an idealized multicomponent SAP fiber
of the present invention is analogous to a liquid emulsion wherein
small droplets of a first liquid, i.e., the dispersed phase, are
dispersed in a second liquid, i.e., the continuous phase. The first
and second liquids are immiscible, and the first liquid, therefore,
is homogeneously dispersed in the second liquid. The first liquid
can be water or oil based, and conversely, the second liquid is oil
or water based, respectively.
[0062] Therefore, in one embodiment, the multicomponent SAP fibers
of the present invention can be envisioned as one or more
microdomains of an acidic resin dispersed in a continuous phase of
a basic resin, or as one or more microdomains of a basic resin
dispersed in a continuous acid resin. These idealized
multicomponent SAP fibers are illustrated in FIG. 1 showing a cross
section of an SAP fiber 10 having discrete microdomains 14 of a
dispersed resin in a continuous phase of a second resin 12. If
microdomains 14 comprise an acidic resin, then continuous phase 12
comprises a basic resin. Conversely, if microdomains 14 comprise a
basic resin, then continuous phase 12 is an acidic resin.
[0063] In another embodiment, the SAP fibers are envisioned as
microdomains of an acidic resin and microdomains of a basic resin
dispersed throughout each particle, without a continuous phase.
This embodiment is illustrated in FIG. 2, showing a cross section
of an idealized multicomponent SAP fiber 20 having a plurality of
microdomains of an acidic resin 22 and a plurality of microdomains
of a basic resin 24 dispersed throughout fiber 20.
[0064] In yet another embodiment, microdomains of the acidic and
basic resins are dispersed throughout a continuous phase comprising
a matrix resin. This embodiment also is illustrated in FIG. 1
wherein multicomponent SAP fiber 10 contains one or more
microdomains 14, each an acidic resin or a basic resin, dispersed
in a continuous phase 12 of a matrix resin.
[0065] It should be understood that the microdomains within each
fiber can be of regular or irregular shape, and that the
microdomains can be dispersed homogeneously or nonhomogeneously
throughout each particle. Accordingly, another important embodiment
of the SAP fiber is illustrated in FIG. 3A, showing an idealized
multicomponent fiber 30 having a core 32 of an acidic
water-absorbing resin surrounded by a sheath 34 of a basic
water-absorbing resin. Conversely, core 32 can comprise a basic
resin, and sheath 34 can comprise an acidic resin.
[0066] FIG. 3B illustrates, in cross section, a similar embodiment
having a core and concentric sheaths that alternate between sheaths
of acidic resin and basic resin. In one embodiment, core 42 and
sheath 46 comprise an acidic water-absorbing resin, and shell 44
comprises a basic water-absorbing resin. Other embodiments include:
core 42 and sheath 46 comprising a basic resin and sheath 44
comprising an acidic resin, or core 42 comprising a matrix resin
and sheaths 44 and 46 comprising an acidic resin and a basic resin
in alternating shells. Other configurations are apparent to persons
skilled in the art, such as increasing the number of shells around
the core.
[0067] FIG. 4A illustrates another embodiment of the present SAP
fibers, in cross section, wherein one microdomain 52 of an acidic
water-absorbing resin is in contact with one microdomain 54 of a
basic water-absorbing resin to provide a multicomponent SAP fiber
50. In this embodiment, a surface of an acidic resin is in contact
with a surface of a microdomain of a basic resin. The embodiment
illustrated in FIG. 4A extends to SAP fibers having more than one
microdomain of each of the acidic resin and the basic resin, as
illustrated in FIG. 4B, wherein, in cross section, multicomponent
SAP fiber 70 contains alternating zones of acidic water-absorbing
resin 72 and basic water-absorbing resin 74. Fiber 70 also can
contain one or more layers 72 or 74 comprising a matrix resin.
[0068] In another embodiment, the multicomponent SAP fiber
comprises individual filaments of acidic resin and basic resin that
are twisted together in the form of a rope. This embodiment is
illustrated in FIGS. 5A and B, which illustrate a "twisted rope"
embodiment of the present SAP fibers lengthwise and in cross
section, respectively. In FIGS. 5A and B, a multicomponent SAP
particle 80 comprises a filament 82 of acidic water-absorbing resin
and a filament 84 of basic water-absorbing resin. Filaments 82 and
84 are in contact along zone of contact 86, thereby placing the
acidic and basic resins in contact.
[0069] The "twisted rope" SAP fibers of FIGS. 5A and B also can be
an embodiment wherein acidic resin filament 82 contains
microdomains of a basic water-absorbing resin, i.e., is a
multicomponent SAP fiber itself, and/or basic resin filament 84
contains microdomains of an acidic water-absorbing resin, i.e.,
also is a multicomponent SAP fiber itself. Filaments 82 and 84 then
are intertwined to form multicomponent SAP fiber 80.
[0070] The embodiment of FIGS. 5A and B also can be a filament 82
and/or a filament 84 comprising a matrix resin having microdomains
of acidic resin and/or basic resin. In this embodiment, filament 82
contains microdomains of an acidic resin, or microdomains of an
acidic and a basic resin, and filament 84 contains microdomains of
a basic resin, or microdomains of an acidic resin and a basic
resin.
[0071] The multicomponent SAP fibers of the present invention
comprise an acidic resin and a basic resin in a weight ratio of
about 95:5 to about 5:95, and preferably about 15:85 to about
85:15. To achieve the full advantage of the present invention, the
weight ratio of acidic resin to basic resin in a multicomponent SAP
fiber is about 30:70 to about 70:30. The acidic and basic resins
can be distributed homogeneously or nonhomogeneously throughout the
SAP fiber.
[0072] The present multicomponent SAP fibers contain at least about
50%, and preferably at least about 70%, by weight of acidic resin
plus basic resin. To achieve the full advantage of the present
invention, a multicomponent SAP fiber contains about 80% to 100% by
weight of the acidic resin plus basic resin. Components of the
present SAP fibers, other than the acidic and basic resin,
typically, are matrix resins or other minor optional
ingredients.
[0073] The multicomponent SAP fibers of the present invention can
be of any cross-sectional geometry. The multicomponent SAP fibers
can be prepared using an extrusion step. In such a case, the shape
of the SAP fiber is determined by the shape of the extrusion die.
The shape of the multicomponent SAP fibers also can be determined
by other methods of preparing the particles, such wet or dry
spinning, which are the preferred methods of preparation.
[0074] In accordance with the present invention, a microdomain is
defined as a volume of an acidic resin or a basic resin that is
present in a multicomponent SAP fiber. Because each multicomponent
SAP particle contains at least one microdomain of an acidic resin,
and at least one microdomain of a basic resin, a microdomain has a
volume that is less than the volume of the multicomponent SAP
fiber. A microdomain, therefore, can be as large as about 90% of
the volume of multicomponent SAP fibers.
[0075] The multicomponent SAP fibers of the present invention are
elongated, acicular SAP particles. The fiber can be in the shape of
a cylinder, for example, having a minor dimension (i.e., diameter)
and a major dimension (i.e., length). The fiber also can be in the
form of a long filament that can be woven. Such filament-like
fibers have a weight of below about 80 decitex, and preferably
below about 70 decitex, per filament, for example, about 2 to about
60 decitex per filament. Tex is the weight in grams per one
kilometer of fiber. One tex equals 10 decitex. For comparison,
poly(acrylic acid) is about 0.78 decitex (0.078 tex), and
poly(vinylamine) is about 6.1 decitex (0.61 tex).
[0076] Cylindrical multicomponent SAP fibers have a minor dimension
(i.e., diameter of the fiber) less than about 1 mm, usually less
than about 500 .mu.m, and preferably less than 250 .mu.m, down to
about 10 .mu.m. The cylindrical SAP fibers can have a relatively
short major dimension, for example, about 1 mm, e.g., in a fibril,
lamella, or flake-shaped article, but generally the fiber has a
length of about 3 to about 100 mm. The filament-like fibers have a
ratio of major dimension to minor dimension of at least 500 to 1,
and preferably at least 1000 to 1, for example, up to and greater
than 10,000 to 1.
[0077] Typically, a microdomain within a fiber or a filament of a
fiber has a diameter of about 750 .mu.m or less, and preferably
about 100 .mu.m or less. To achieve the full advantage of the
present invention, a microdomain has a diameter of about 20 .mu.m
or less. The multicomponent SAP fibers also contain microdomains
that have submicron diameters, e.g., microdomain diameters of less
than 1 .mu.m to about 0.01 .mu.m. In other embodiments, the
microdomain can be the entire filament of a twisted rope SAP fiber.
Microdomains also can be the core and the sheath in the embodiments
illustrated in FIGS. 3A and B.
[0078] Each multicomponent SAP fiber contains one or more
microdomains of an acidic water-absorbing resin and one or more
microdomains of a basic water-absorbing resin, either in contact or
in close proximity to one another. As illustrated hereafter, the
microdomain structure of the present SAP fibers provides improved
fluid absorption (both in amount of fluid absorbed and retained,
and rate of absorption) compared to an SAP comprising a simple
mixture of discrete acidic SAP resin fibers and discrete basic SAP
resin fibers. In accordance with another important feature of the
present invention, the present multicomponent SAP fibers also
demonstrate improved permeability, both through an individual fiber
and between fibers. The present SAP fibers, therefore, have an
improved ability to rapidly absorb a fluid, even in "gush"
situations, for example, when used in diapers to absorb urine.
[0079] The features of good permeability, absorption and retention
properties, especially of electrolyte-containing liquids,
demonstrated by the present multicomponent SAP fibers, is important
with respect to practical uses of an SAP. These improved properties
are attributed, in part, to the fact that electrolyte removal from
the liquid is facilitated by contacting a single particle (which,
in effect, performs an essentially simultaneous deionization of the
liquid), as opposed to the liquid having to contact individual
acidic and basic particles (which, in effect, performs a sequential
two-step deionization).
[0080] If a blend of acidic resin fibers and basic resin fibers is
used, the fibers typically have a small particle size. A small
particle size is required to obtain desirable desalination
kinetics, because the electrolyte is removed in a stepwise manner,
with the acidic resin removing the cation and the basic resin
removing the anion. The electrolyte-containing fluid, therefore,
must contact two particles for desalination, and this process is
facilitated by small particle sized SAPs. Small particles, however,
have the effect of reducing flow of the fluid through and between
SAP particles, i.e., permeability is reduced and a longer time is
required to absorb the fluid.
[0081] In addition, in practical use, such as in diapers, SAPs are
used in conjunction with a cellulosic pulp. If a blend of acidic
resin particles and basic resin particles is used as the SAP, the
cellulosic pulp can cause a separation between the acidic resin
particles and basic resin particles, which adversely affects
desalination. The present multidomain SAP fibers overcome this
problem because the acidic resin and basic resin are present in a
single particle. The introduction of cellulosic pulp, therefore,
cannot separate the acidic and basic resin and cannot adversely
affect desalination by the SAP.
[0082] A single multicomponent SAP particle, like a present fiber,
simultaneously desalinates an electrolyte-containing liquid.
Desalination is essentially independent of particle size.
Accordingly, the present multicomponent SAP fibers can be of a
larger size. These features allow for improved liquid permeability
through and between the SAP particles, and results in a more rapid
absorption of the electrolyte-containing liquid.
[0083] The following schematic reactions illustrate the reactions
which occur to deionize, e.g., desalinate, an aqueous saline
solution, and that are performed essentially simultaneously in a
single microcomposite SAP particle, but are performed stepwise in a
simple mixture of acidic and basic resins:
R--CO.sub.2H+NaCl.fwdarw.R--CO.sub.2.sup.-Na.sup.++HCl
[0084] (acidic resin)
R--NH.sub.2+HCl.fwdarw.R--NH.sub.3.sup.+Cl.sup.-
[0085] (basic resin).
[0086] The present multicomponent SAP fibers can be in a form
wherein a microdomain of an acidic water-absorbing resin is in
contact with a microdomain of a basic water-absorbing resin. In
another embodiment, the SAP fibers can be in a form wherein at
least one microdomain of an acidic water-absorbing resin is
dispersed in a continuous phase of a basic water-absorbing resin.
Alternatively, the multicomponent SAP fibers can be in a form
wherein at least one microdomain of a basic resin is dispersed in a
continuous phase of an acidic resin. In another embodiment, at
least one microdomain of one or more acidic resin and at least one
microdomain of one or more basic resin comprise the entire SAP
fiber, and neither type of resin is considered the dispersed or the
continuous phase. In yet another embodiment, at least one
microdomain of an acidic resin and at least one microdomain of a
basic resin are dispersed in a matrix resin.
[0087] An acidic water-absorbing resin present in a multicomponent
SAP fiber can be either a strong or a weak acidic water-absorbing
resin. The acidic water-absorbing resin can be a single resin, or a
mixture of resins. The acidic resin can be a homopolymer or a
copolymer. The identity of the acidic water-absorbing resin is not
limited as long as the resin is capable of swelling and absorbing
at least ten times its weight in water, when in a neutralized form.
The acidic resin is present in its acidic form, i.e., about 75% to
100% of the acidic moieties are present in the free acid form. As
illustrated hereafter, although the free acid form of a acidic
water-absorbing resin is generally a poor water absorbent, the
combination of an acidic resin and a basic resin in a present
multicomponent SAP fiber provides excellent water absorption and
retention properties.
[0088] The acidic water-absorbing resin typically is a lightly
crosslinked acrylic-type resin, such as lightly crosslinked
polyacrylic acid. The lightly crosslinked acidic resin typically is
prepared by polymerizing an acidic monomer containing an acyl
moiety, e.g., acrylic acid, or a moiety capable of providing an
acid group, i.e., acrylonitrile, in the presence of a crosslinker,
i.e., a polyfunctional organic compound. The acidic resin can
contain other copolymerizable units, i.e., other monoethylenically
unsaturated comonomers, well known in the art, as long as the
polymer is substantially, i.e., at least 10%, and preferably at
least 25%, acidic monomer units. To achieve the full advantage of
the present invention, the acidic resin contains at least 50%, and
more preferably, at least 75%, and up to 100%, acidic monomer
units. The other copolymerizable units can, for example, help
improve the hydrophilicity and crosslinking of the polymer.
[0089] Ethylenically unsaturated carboxylic acid and carboxylic
acid anhydride monomers useful in the acidic water-absorbing resin
include acrylic acid, methacrylic acid, ethacrylic acid,
.alpha.-chloroacrylic acid, .alpha.-cyanoacrylic acid,
.beta.-methylacrylic acid (crotonic acid), .alpha.-phenylacrylic
acid, .beta.-acryloxypropionic acid, sorbic acid,
.alpha.-chlorosorbic acid, angelic acid, cinnamic acid,
p-chlorocinnamic acid, .beta.-stearylacrylic acid, itaconic acid,
citraconic acid, mesaconic acid, glutaconic acid, aconitic acid,
maleic acid, fumaric acid, tricarboxyethylene, and maleic
anhydride.
[0090] Ethylenically unsaturated sulfonic acid monomers include
aliphatic or aromatic vinyl sulfonic acids, such as vinylsulfonic
acid, allyl sulfonic acid, vinyl toluene sulfonic acid, styrene
sulfonic acid, acrylic and methacrylic sulfonic acids, such as
sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate,
sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropyl sulfonic
acid, and 2-acrylamide-2-methylpr- opane sulfonic acid.
[0091] As set forth above, polymerization of acidic monomers, and
copolymerizable monomers, if present, most commonly is performed by
free radical processes in the presence of a polyfunctional organic
compound. The acidic resins are crosslinked to a sufficient extent
such that the polymer is water insoluble. Crosslinking renders the
acidic resins substantially water insoluble, and, in part, serves
to determine the absorption capacity of the resins. For use in
absorption applications, an acidic resin is lightly crosslinked,
i.e., has a crosslinking density of less than about 20%, preferably
less than about 10%, and most preferably about 0.01% to about
7%.
[0092] A crosslinking agent most preferably is used in an amount of
less than about 7 wt %, and typically about 0.1 wt % to about 5 wt
%, based on the total weight of monomers. Examples of crosslinking
polyvinyl monomers include, but are not limited to, polyacrylic (or
polymethacrylic) acid esters represented by the following formula
(III); and bisacrylamides, represented by the following formula
(IV). 3
[0093] wherein x is ethylene, propylene, trimethylene, cyclohexyl,
hexamethylene, 2-hydroxypropylene,
--(CH.sub.2CH.sub.2O).sub.nCH.sub.2CH.- sub.2--, or 4
[0094] n and m are each an integer 5 to 40, and k is 1 or 2; 5
[0095] wherein 1 is 2 or 3.
[0096] The compounds of formula (III) are prepared by reacting
polyols, such as ethylene glycol, propylene glycol,
trimethylolpropane, 1,6-hexanediol, glycerin, pentaerythritol,
polyethylene glycol, or polypropylene glycol, with acrylic acid or
methacrylic acid. The compounds of formula (IV) are obtained by
reacting polyalkylene polyamines, such as diethylenetriamine and
triethylenetetramine, with acrylic acid.
[0097] Specific crosslinking monomers include, but are not limited
to, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate,
1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate,
diethylene glycol diacrylate, diethylene glycol dimethacrylate,
ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A
dimethacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol
diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol
dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol
dimethacrylate, triethylene glycol diacrylate, triethylene glycol
dimethacrylate, tripropylene glycol diacrylate, tetraethylene
glycol diacrylate, tetraethylene glycol dimethacrylate,
dipentaerythritol pentaacrylate, pentaerythritol tetraacrylate,
pentaerythritol triacrylate, trimethylolpropane triacrylate,
trimethylolpropane trimethacrylate,
tris(2-hydroxyethyl)isocyanurate triacrylate,
tris(2-hydroxyethyl)isocyanurate trimethacrylate, divinyl esters of
a polycarboxylic acid, diallyl esters of a polycarboxylic acid,
triallyl terephthalate, diallyl maleate, diallyl fumarate,
hexamethylenebismaleimide, trivinyl trimellitate, divinyl adipate,
diallyl succinate, a divinyl ether of ethylene glycol,
cyclopentadiene diacrylate, tetraallyl ammonium halides, or
mixtures thereof. Compounds such as divinylbenzene and divinyl
ether also can be used to crosslink the poly(dialkylaminoalkyl
acrylamides). Especially preferred crosslinking agents are
N,N'-methylenebisacrylamide, N,N'-methylenebismethacrylamide,
ethylene glycol dimethacrylate, and trimethylolpropane
triacrylate.
[0098] The acidic resin, either strongly acidic or weakly acidic,
can be any resin that acts as an SAP in its neutralized form. The
acidic resins typically contain a plurality of carboxylic acid,
sulfonic acid, phosphonic acid, phosphoric acid, and/or sulfuric
acid moieties. Examples of acidic resins include, but are not
limited to, polyacrylic acid, hydrolyzed starch-acrylonitrile graft
copolymers, starch-acrylic acid graft copolymers, saponified vinyl
acetate-acrylic ester copolymers, hydrolyzed acrylonitrile
copolymers, hydrolyzed acrylamide copolymers, ethylene-maleic
anhydride copolymers, isobutylene-maleic anhydride copolymers,
poly(vinylsulfonic acid), poly(vinylphosphonic acid),
poly(vinylphosphoric acid), poly(vinylsulfuric acid), sulfonated
polystyrene, poly(aspartic acid), poly(lactic acid), and mixtures
thereof. The preferred acidic resins are the polyacrylic acids.
[0099] The multicomponent SAP fibers can contain individual
microdomains that: (a) contain a single acidic resin or (b) contain
more than one, i.e., a mixture, of acidic resins. The
multicomponent SAP fibers also can contain microdomains wherein,
for the acidic component, a portion of the acidic microdomains
comprise a first acidic resin or acidic resin mixture, and the
remaining portion comprises a second acidic resin or acidic resin
mixture.
[0100] Analogous to the acidic resin, the basic water-absorbing
resin in the present SAP fibers can be a strong or weak basic
water-absorbing resin. The basic water-absorbing resin can be a
single resin or a mixture of resins. The basic resin can be a
homopolymer or a copolymer. The identity of the basic resin is not
limited as long as the basic resin is capable of swelling and
absorbing at least 10 times its weight in water, when in a charged
form. The weak basic resin typically is present in its free base,
or neutral, form, i.e., about 75% to about 100% of the basic
moieties, e.g., amino groups, are present in a neutral, uncharged
form. The strong basic resins typically are present in the
hydroxide (OH) or bicarbonate (HCO.sub.3) form.
[0101] The basic water-absorbing resin typically is a lightly
crosslinked acrylic type resin, such as a poly(vinylamine) or a
poly(dialkylaminoalkyl (meth)acrylamide). The basic resin also can
be a polymer such as a lightly crosslinked polyethylenimine, a
poly(allylamine), a poly(allylguanidine), a
poly(dimethyldiallylammonium hydroxide), a quaternized polystyrene
derivative, such as 6
[0102] a guanidine-modified polystyrene, such as 7
[0103] a quaternized poly((meth)acrylamide) or ester analog, such
as 8
[0104] wherein Me is methyl, R.sub.2 is hydrogen or methyl, n is a
number 1 to 8, and q is a number from 10 to about 100,000, or a
poly(vinylguanidine), i.e., poly(VG), a strong basic
water-absorbing resin having the general structural formula (V)
9
[0105] wherein q is a number from 10 to about 100,000, and R.sub.5
and R.sub.6, independently, are selected from the group consisting
of hydrogen, C.sub.1-C.sub.4 alkyl, C.sub.3-C.sub.6 cycloalkyl,
benzyl, phenyl, alkyl-substituted phenyl, naphthyl, and similar
aliphatic and aromatic groups. The lightly crosslinked basic
water-absorbing resin can contain other copolymerizable units and
is cross-linked using a polyfunctional organic compound, as set
forth above with respect to the acidic water-absorbing resin.
[0106] A basic water-absorbing resin used in the present SAP fibers
typically contains an amino or a guanidino group. Accordingly, a
water-soluble basic resin also can be crosslinked in solution by
suspending or dissolving an uncrosslinked basic resin in an aqueous
or alcoholic medium, then adding a di- or polyfunctional compound
capable of crosslinking the basic resin by reaction with the amino
groups of the basic resin. Such crosslinking agents include, for
example, multifunctional aldehydes (e.g., glutaraldehyde),
multifunctional acrylates (e.g., butanediol diacrylate, TMPTA),
halohydrins (e.g., epichlorohydrin), dihalides (e.g.,
dibromopropane), disulfonate esters (e.g.,
ZA(O.sub.2)O--(CH.sub.2).sub.n--OS(O).sub.2Z, wherein n is 1 to 10,
and Z is methyl or tosyl), multifunctional epoxies (e.g., ethylene
glycol diglycidyl ether), multifunctional esters (e.g., dimethyl
adipate), multifunctional acid halides (e.g., oxalyl chloride),
multifunctional carboxylic acids (e.g., succinic acid), carboxylic
acid anhydrides (e.g., succinic anhydride), organic titanates
(e.g., TYZOR AA from DuPont), melamine resins (e.g., CYMEL 301,
CYMEL 303, CYMEL 370, and CYMEL 373 from Cytec Industries, Wayne,
N.J.), hydroxymethyl ureas (e.g.,
N,N'-dihydroxymethyl-4,5-dihydroxyethyleneurea), and
multifunctional isocyanates (e.g., toluene diisocyanate or
methylene diisocyanate). Crosslinking agents also are disclosed in
Pinschmidt, Jr. et al. U.S. Pat. No. 5,085,787, incorporated herein
by reference, and in EP 450 923.
[0107] Conventionally, the crosslinking agent is water or alcohol
soluble, and possesses sufficient reactivity with the basic resin
such that crosslinking occurs in a controlled fashion, preferably
at a temperature of about 25.degree. C. to about 150.degree. C.
Preferred crosslinking agents are ethylene glycol diglycidyl ether
(EGDGE), a water-soluble diglycidyl ether, and a dibromoalkane, an
alcohol-soluble compound.
[0108] The basic resin, either strongly or weakly basic, therefore,
can be any resin that acts as an SAP in its charged form. The basic
resin typically contains amino or guanidino moieties. Examples of
basic resins include a poly(vinylamine), a polyethylenimine, a
poly(vinylguanidine), a poly(allylamine), a poly(allylguanidine),
or a poly(dialkylaminoalkyl (meth)acrylamide) prepared by
polymerizing and lightly crosslinking a monomer having the
structure 10
[0109] wherein R.sub.1 and R.sub.2, independently, are selected
from the group consisting of hydrogen and methyl, Y is a divalent
straight chain or branched organic radical having 1 to 8 carbon
atoms, and R.sub.3 and R.sub.4, independently, are alkyl radicals
having 1 to 4 carbon atoms. Preferred basic resins include a
poly(vinylamine), polyethylenimine, poly(vinylguanadine),
poly(dimethylaminoethyl acrylamide) (poly(DAEA)), and
poly(dimethylaminopropyl methacrylamide) (poly(DMAPMA)). Analogous
to microdomains of an acidic resin, the present multicomponent SAPs
can contain microdomains of a single basic resin, microdomains
containing a mixture of basic resins, or microdomains of different
basic resins.
[0110] The present multicomponent SAP fibers can be prepared by
various methods, and the method of preparing a multicomponent SAP
fiber is not limited by the following embodiments. Any method that
provides a fiber having at least one microdomain of an acidic resin
in contact with or in close proximity to at least one microdomain
of a basic resin is suitable.
[0111] In one method, dry particles of a basic resin, optionally
surface crosslinked and/or annealed, are admixed into a rubbery gel
of an acidic resin. The resulting mixture is extruded, then dried,
and optionally surface crosslinked and/or annealed, to provide
multicomponent SAP fibers having microdomains of a basic resin
dispersed in a continuous phase of an acidic resin. Alternatively,
particles of an acidic resin, optionally surface crosslinked and/or
annealed, can be admixed into a rubbery gel of a basic resin, and
the resulting mixture is extruded and dried, and optionally surface
crosslinked and/or annealed, to provide multicomponent SAP fibers
having microdomains of an acidic resin dispersed in a continuous
phase of a basic resin.
[0112] In another method, dry particles of an acidic resin can be
admixed with dry particles of a basic resin, and the resulting
mixture is formed into a hydrogel, then extruded, to form
multicomponent SAP fibers.
[0113] In yet another method, a rubbery gel of an acidic resin and
a rubbery gel of a basic resin, each optionally surface crosslinked
and/or annealed, are coextruded, and the coextruded product is
dried, and optionally surface crosslinked and/or annealed, to form
multicomponent SAP fibers containing microdomains of the acidic
resin and the basic resin, as illustrated in FIGS. 3 and 4.
[0114] Another method utilizes spinning technology, wherein a first
polymer, e.g., poly(vinylamine), is spun in the form of a filament,
then the freshly spun filament is coated with a second polymer,
e.g., poly(acrylic acid), to form (after drying) a core-sheath
multicomponent SAP fiber.
[0115] In yet another method, a filament of an acidic resin is
prepared by standard spinning techniques, and a filament of a basic
resin is prepared by standard spinning techniques. The two
filaments then are twisted together, before and/or after optional
surface crosslinking and annealing, and then dried and formed into
multicomponent SAP fibers, as illustrated in FIG. 5.
[0116] The method of preparing the present multicomponent SAP
fibers, therefore, typically utilizes, but does not require, a
spinning or an extrusion step. Other methods of preparation wherein
the multicomponent SAP fiber contains at least one microdomain of
an acidic resin and at least one microdomain of a basic resin in
contact or in close proximity with each other also can be used.
[0117] In embodiments wherein an acidic resin and a basic resin are
present as microdomains within a matrix of a matrix resin,
particles of an acidic resin and a basic resin are admixed with a
rubbery gel of a matrix resin, and the resulting mixture is
extruded, then dried, to form multicomponent SAP fibers having
microdomains of an acidic resin and a basic resin dispersed in a
continuous phase of a matrix resin. Alternatively, rubbery gels of
an acidic resin, basic resin, and matrix resin can be coextruded to
provide a multicomponent SAP fibers containing microdomains of an
acidic resin, a basic resin, and a matrix resin. In this
embodiment, the acidic resin, basic resin, and resulting
multicomponent SAP fibers, each can be optionally surface
crosslinked and/or annealed. Similarly, the matrix resin, acidic
resin, and basic resin can be spun to form a core-sheath or twisted
SAP fiber embodiment of the multicomponent SAP fibers.
[0118] The matrix resin is any resin that allows fluid transport
such that a liquid medium can contact the acidic and basic resin.
The matrix resin typically is a hydrophilic resin capable of
absorbing water. Nonlimiting examples of matrix resins include
poly(vinyl alcohol), poly(N-vinylformamide), polyethylene oxide,
poly(meth)acrylamide, poly(hydroxyethyl acrylate),
hydroxyethylcellulose, methylcellulose, and mixtures thereof. The
matrix resin also can be a conventional water-absorbing resin, for
example, a polyacrylic acid neutralized greater than 25 mole %, and
typically greater than 50 mole %.
[0119] In preferred embodiments, the acidic resin, the basic resin,
and/or the multicomponent SAP particles are surface treated and/or
annealed. Surface treatment and/or annealing results in surface
crosslinking of the particle. In especially preferred embodiments,
the acidic and/or basic resins comprising the multicomponent SAP
fibers are surface treated and/or annealed, and the entire
multicomponent SAP fiber is surface treated and/or annealed. It has
been found that surface treating and/or annealing of an acidic
resin, a basic resin, and/or a multicomponent SAP fiber of the
present invention enhances the ability of the resin or
multicomponent SAP fiber to absorb and retain aqueous media under a
load.
[0120] Surface crosslinking is achieved by contacting an acidic
resin, a basic resin, and/or a multicomponent SAP fiber with a
solution of a surface crosslinking agent to wet predominantly only
the outer surfaces of the resin or SAP particle. Surface
crosslinking and drying of the resin or multicomponent SAP particle
then is performed, preferably by heating at least the wetted
surfaces of the resin or multicomponent SAP fibers.
[0121] Typically, the resins and/or SAP fibers are surface treated
with a solution of a surface cross-linking agent. The solution
contains about 0.01% to about 4%, by weight, surface crosslinking
agent, and preferably about 0.4% to about 2%, by weight, surface
crosslinking agent in a suitable solvent, for example, water or an
alcohol. The solution can be applied as a fine spray onto the
surface of freely tumbling resin particles or multicomponent SAP
particles at a ratio of about 1:0.01 to about 1:0.5 parts by weight
resin or SAP particles to solution of surface crosslinking agent.
The surface crosslinker is present in an amount of 0% to about 5%,
by weight of the resin or SAP fiber, and preferably 0% to about
0.5% by weight. To achieve the full advantage of the present
invention, the surface crosslinker is present in an amount of about
0.001% to about 0.1% by weight.
[0122] The crosslinking reaction and drying of the surface-treated
resin or multicomponent SAP fibers are achieved by heating the
surface-treated polymer at a suitable temperature, e.g., about
25.degree. C. to about 150.degree. C., and preferably about
105.degree. C. to about 120.degree. C. However, any other method of
reacting the crosslinking agent to achieve surface crosslinking of
the resin or multicomponent SAP fibers, and any other method of
drying the resin or multicomponent SAP fibers, such as microwave
energy, or the such as, can be used.
[0123] With respect to the basic resin, or multicomponent SAP
fibers having a basic resin present on the exterior of the fibers,
suitable surface crosslinking agents include di- or polyfunctional
molecules capable of reacting with amino groups and crosslinking a
basic resin. Preferably, the surface crosslinking agent is alcohol
or water soluble and possesses sufficient reactivity with a basic
resin such that crosslinking occurs in a controlled fashion at a
temperature of about 25.degree. C. to about 150.degree. C.
[0124] Nonlimiting examples of suitable surface crosslinking agents
for basic resins include:
[0125] (a) dihalides and disulfonate esters, for example, compounds
of the formula
Y--(CH.sub.2).sub.p--Y,
[0126] wherein p is a number from 2 to 12, and Y, independently, is
halo (preferably bromo), tosylate, mesylate, or other alkyl or aryl
sulfonate esters;
[0127] (b) multifunctional aziridines;
[0128] (c) multifunctional aldehydes, for example, glutaraldehyde,
trioxane, paraformaldehyde, terephthaldehyde, malonaldehyde, and
glyoxal, and acetals and bisulfites thereof;
[0129] (d) halohydrins, such as epichlorohydrin;
[0130] (e) multifunctional epoxy compounds, for example, ethylene
glycol diglycidyl ether, bisphenol A diglycidyl ether, and
bisphenol F diglycidyl ether,
[0131] (f) multifunctional carboxylic acids and esters, acid
chlorides, and anhydrides derived therefrom, for example, di- and
polycarboxylic acids containing 2 to 12 carbon atoms, and the
methyl and ethyl esters, acid chlorides, and anhydrides derived
therefrom, such as oxalic acid, adipic acid, succinic acid,
dodecanoic acid, malonic acid, and glutaric acid, and esters,
anhydrides, and acid chlorides derived therefrom;
[0132] (g) organic titanates, such as TYZOR AA, available from E.
I. DuPont de Nemours, Wilmington, Del.;
[0133] (h) melamine resins, such as the CYMEL resins available from
Cytec Industries, Wayne, N.J.;
[0134] (i) hydroxymethyl ureas, such as
N,N'-dihydroxymethyl-4,5-dihydroxy- ethylene urea;
[0135] (j) multifunctional isocyanates, such as toluene
diisocyanate, isophorone diisocyanate, methylene diisocyanate,
xylene diisocyanate, and hexamethylene diisocyanate; and
[0136] (k) other crosslinking agents for basic water-absorbing
resins known to persons skilled in the art.
[0137] A preferred surface crosslinking agent is a dihaloalkane,
ethylene glycol diglycidyl ether (EGDGE), or a mixture thereof,
which crosslink a basic resin at a temperature of about 25.degree.
C. to about 150.degree. C. Especially preferred surface
crosslinking agents are dibromoalkanes containing 3 to 10 carbon
atoms and EGDGE.
[0138] With respect to the acidic water-absorbing resins, or
multicomponent SAP particles having an acidic resin on the exterior
of the fibers, suitable surface crosslinking agents are capable of
reacting with acid moieties and crosslinking the acidic resin.
Preferably, the surface crosslinking agent is alcohol soluble or
water soluble, and possesses sufficient reactivity with an acidic
resin such that crosslinking occurs in a controlled fashion,
preferably at a temperature of about 25.degree. C. to about
150.degree. C.
[0139] Nonlimiting examples of suitable surface crosslinking agents
for acidic resins include:
[0140] (a) polyhydroxy compounds, such as glycols and glycerol;
[0141] (b) metal salts;
[0142] (c) quaternary ammonium compounds;
[0143] (d) a multifunctional epoxy compound;
[0144] (e) an alkylene carbonate, such as ethylene carbonate or
propylene carbonate;
[0145] (f) a polyaziridine, such as 2,2-bishydroxymethyl butanol
tris[3-(1-aziridine propionate]);
[0146] (g) a haloepoxy, such as epichlorhydrin;
[0147] (h) a polyamine, such as ethylenediamine;
[0148] (i) a polyisocyanate, such as 2,4-toluene diisocyanate;
and
[0149] (j) other crosslinking agents for acidic water-absorbing
resins known to persons skilled in the art.
[0150] In addition to, or in lieu of, surface treating, the acidic
resin, the basic resin, the matrix resin, the entire SAP fiber, or
any combination thereof can be annealed to improve water absorption
and retention properties under a load. It has been found that
heating a resin for a sufficient time at a sufficient temperature
above the Tg (glass transition temperature) of the resin or
microdomains improves the absorption properties of the resin. FIGS.
6 and 7 contain graphs showing the effect of annealing time and
temperature on the absorption properties of multicomponent SAP
granules comprising 55% by weight poly(vinylamine) and 45% by
weight poly(acrylic acid). Typically, a multicomponent SAP fiber of
the present invention is subjected to a sufficient temperature for
a sufficient time to heat and anneal the external and the internal
portions of the fiber.
[0151] The graphs in FIGS. 6 and 7 show that heating a
multicomponent SAP granule for about 20 to about 120 minutes at a
temperature of about 60.degree. C. to about 150.degree. C. improves
absorption properties. The absorption properties, i.e., AUL and
AUNL, graphed in FIGS. 6 and 7 are discussed in detail hereafter.
Preferably, annealing is performed for about 30 to about 100
minutes at about 80.degree. C. to about 140.degree. C. To achieve
the full advantage of annealing, the SAP fibers are annealed for
about 40 to about 90 minutes at about 100.degree. C. to about
140.degree. C.
[0152] In accordance with an important feature of the present
invention, a strong acidic resin can be used with either a strong
basic resin or a weak basic resin, or a mixture thereof. A weak
acidic resin can be used with a strong basic resin or a weak basic
resin, or a mixture thereof. Preferably, the acidic resin is a weak
acidic resin and the basic resin is a weak basic resin. This result
is unexpected in view of the ion exchange art wherein a combination
of a weak acidic resin and a weak basic resin does not perform as
well as other combinations, e.g., a strong acidic resin and a
strong basic resin. In more preferred embodiments, the weak acidic
resin, the weak basic resin, and/or the multicomponent SAP fibers
are surface crosslinked and/or annealed.
[0153] As previously discussed, sodium poly(acrylate)
conventionally is considered the best SAP, and, therefore, is the
most widely used SAP in commercial applications. Sodium
poly(acrylate) has polyelectrolytic properties that are responsible
for its superior performance in absorbent applications. These
properties include a high charge density, and charge relatively
close to the polymer backbone.
[0154] However, an acidic resin in the free acid form, or a basic
resin in the free base form, typically do not function as a
commercially useful SAP because there is no ionic charge on either
type of polymer. A poly(acrylic acid) resin, or a poly(vinylamine)
resin, are neutral polymers, and, accordingly, do not possess the
polyelectrolytic properties necessary to provide SAPs useful
commercially in diapers, catamenial devices, and similar absorbent
articles. The driving force for water absorption and retention,
therefore, is lacking. This is illustrated in Tables 3 and 4
showing the relatively poor absorption and retention properties for
a neutral poly(DAEA) in absorbing synthetic urine. However, when
converted to a salt, an acidic resin, such as a polyacrylic acid,
or a basic resin, such as a poly(dialkylaminoalkyl
(meth)acrylamide), then behave such as a commercially useful
SAP.
[0155] It has been found that basic resins, in their free base
form, are useful components in super-absorbent materials further
containing an acidic water-absorbing resin. For example, a
superabsorbent material comprising an admixture of a
poly(dialkylaminoalkyl (meth)acrylamide) and an acidic
water-absorbing resin, such as polyacrylic acid, demonstrates good
water absorption and retention properties. Such an SAP material
comprises two uncharged, slightly crosslinked polymers, each of
which is capable of swelling and absorbing aqueous media. When
contacted with water or an aqueous electrolyte-containing medium,
the two uncharged polymers neutralize each other to form a
superabsorbent material. This also reduces the electrolyte content
of the medium absorbed by polymer, further enhancing the
polyelectrolyte effect. Neither polymer in its uncharged form
behaves as an SAP by itself when contacted with water. However,
superabsorbent materials, which contain a simple mixture of two
resins, one acidic and one basic, are capable of acting as an
absorbent material because the two resins are converted to their
polyelectrolyte form. These superabsorbent materials have
demonstrated good water absorption and retention properties.
[0156] In the present multicomponent SAP fibers, the weak basic
resin is present in its free base, e.g., amine, form, and the
acidic resin is present in its free acid form. It is envisioned
that a low percentage, i.e., about 25% or less, of the amine and/or
acid functionalities can be in their charged form. The low
percentage of charged functionalities does not adversely affect
performance of the SAP fibers, and can assist in the initial
absorption of a liquid. A strong basic resin is present in the
hydroxide or bicarbonate, i.e., charged, form.
[0157] The present multicomponent SAP fibers are useful in articles
designed to absorb large amounts of liquids, especially
electrolyte-containing liquids, such as in diapers and catamenial
devices.
[0158] The following nonlimiting examples illustrate the
preparation of the multicomponent SAP fibers of the present
invention. In the test results set forth herein, the multicomponent
SAP particles of the present invention were tested for absorption
under no load (AUNL) and absorption under load at 0.28 psi and 0.7
psi (AUL (0.28 psi) and AUL (0.7 psi)). Absorption under load (AUL)
is a measure of the ability of an SAP to absorb fluid under an
applied pressure. The AUL was determined by the following method,
as disclosed in U.S. Pat. No. 5,149,335, incorporated herein by
reference.
[0159] An SAP (0.160 g.+-.0.001 g) is carefully scattered onto a
140-micron, water-permeable mesh attached to the base of a hollow
Plexiglas cylinder with an internal diameter of 25 mm. The sample
is covered with a 100 g cover plate and the cylinder assembly
weighed. This gives an applied pressure of 20 g/cm.sup.2 (0.28 psi)
. Alternatively, the sample can be covered with a 250 g cover plate
to give an applied pressure of 51 g/cm.sup.2 (0.7 psi). The
screened base of the cylinder is placed in a 100 mm petri dish
containing 25 milliliters of a test solution (usually 0.9% saline),
and the polymer is allowed to absorb for 1 hour (or 3 hours). By
reweighing the cylinder assembly, the AUL (at a given pressure) is
calculated by dividing the weight of liquid absorbed by the dry
weight of polymer before liquid contact.
EXAMPLE 1
Preparation of Poly(acrylic acid) Particles 0% Neutralized
(Poly(AA) DN=0)
[0160] A monomer mixture containing acrylic acid (270 grams),
deionized water (810 grams), methylene-bisacrylamide (0.4 grams),
sodium persulfate (0.547 grams), and
2-hydroxy-2-methyl-1-phenyl-propan-1-one (0.157 grams) was
prepared, then sparged with nitrogen for 15 minutes. The monomer
mixture was placed into a shallow glass dish, then the monomer
mixture was polymerized at an initiation temperature of 10.degree.
C. under 20 mW/cm.sup.2 of UV light for about 12 to about 15
minutes. The resulting poly(AA) was a rubbery gel.
[0161] The rubbery poly(AA) gel was cut into small pieces, then
extruded three times through a KitchenAid Model K5SS mixer with
meat grinder attachment. During extrusion, sodium metabisulfite was
added to gel to react with unreacted monomer. The extruded gel was
dried in a forced-air oven at 145.degree. C. for 90 minutes, and
finally ground and sized through sieves to obtain the desired
particle size of about 180 to about 710 .mu.m (microns).
[0162] This procedure provided a lightly crosslinked polyacrylic
acid with a degree of neutralization of zero (DN=0). The
polyacrylid acid (DN=0) absorbed 119.5 g of 0.1 M sodium hydroxide
(NaOH) per gram of polymer and 9.03 g synthetic urine per gram of
polymer under a load of 0.7 psi.
EXAMPLE 2
Preparation of a Crosslinked Poly(vinylamine) Resin Particles
[0163] To 100 g of an 8% by weight aqueous poly(vinylamine)
solution was added about 2 mol % (0.66 g) of ethylene glycol
diglycidyl ether (EGDGE). The resulting mixture was stirred for
about 5 minutes to dissolve the EGDGE, then the homogeneous mixture
was placed in an oven, heated to about 60.degree. C., and held for
two hours to gel. The resulting gel then was extruded three times,
and dried to a constant weight at 60.degree. C. The dried, lightly
crosslinked poly(vinylamine) (poly(VAm)) then was cryogenically
milled to form a granular material (about 180 to about 710 .mu.m).
The crosslinked poly(VAm) absorbed 59.12 g/g of 0.1 M hydrochloric
acid under no load, and 17.3 g/g of synthetic urine under a load of
0.7 psi.
EXAMPLE 3
Preparation of Poly(acrylic acid) Fibers by Dry Spinning
[0164] A spinning solution was prepared by concentrating an aqueous
35% (w/w) solution of uncrosslinked poly(acrylic acid) (poly(AA)),
molecular weight about 250,000, to 55% (w/w). To this solution was
added EGDGE (0.5% to 5% mol/mol poly(AA)) and triethylamine (5%
mol/mol poly(AA)), and the resulting mixture was mixed to produce a
homogeneous spinning solution. The viscosity of the spinning
solution, at 55% (w/w), was 13,000 cps (by Reverse Flow Viscometer,
size 8, at 25.degree. C.). The spinning solution was placed in a
Petri dish and fibers were drawn vertically upwards to a rotating
drum (diameter of 15.5 cm). The dry spinning apparatus is
illustrated in FIG. 8. The pull off speed was about 54 rpm with a
filament draw length of 500 mm. The drawn fibers were cured either
by microwave using 720 watts (W) power (2 minutes for 5% EGDGE) or
by a conventional fan-assisted oven at 60.degree. C. (60 minutes
for 5% EGDGE). The time needed to cure the fiber was dependent upon
the concentration of EGDGE. In the preparation of poly(AA) by dry
spinning, the concentration of EGDGE in the spinning solution
typically is about 0.5 to about 5% (mol/mol poly(AA)). The addition
of triethylamine as a cure catalyst resulted in a faster cure,
which occurred at a lower temperature.
[0165] The resulting poly(AA) fibers were about 25 .mu.m in
diameter and 0.71 denier (0.078 tex). The fibers absorbed about
69.9 g/g of 0.1 M NaOH at no load after 1 hour, and about 17.6 g/g
of synthetic urine at 0.28 psi after 1 hour.
EXAMPLE 4
Preparation of Poly(vinylamine) Fibers by Wet Spinning
[0166] A spinning solution was prepared by concentrating a 6% w/w
aqueous solution of poly(VAm) to 10% w/w poly(VAm) (molecular
weight about 190,000). EGDGE (0.025 mol %) was added to the
poly(VAm) solution, and mixed to provide a homogeneous solution.
The solution then was heated for about 30 minutes at about
40.degree. C., and was spinnable. The resulting spinning solution
was introduced directly into a coagulation bath through a
spinnerette submersed in a coagulating medium. The coagulation
medium in the coagulation bath contained a mixture of EGDGE,
typically 0.5% (w/w), and acetone. The concentration of EGDGE
typically is about 0.5 to about 5% (w/w). The spinning solution was
placed in a syringe fitted with a 23 gauge needle. The poly(VAm)
was injected into the coagulating medium at a flow rate of 0.02
ml/min, and the resulting poly(VAm) was drawn off at a wind-up rate
of 64 rpm. The diameter of the drum was 12 cm. The wet spinning
apparatus is illustrated in FIG. 9. The poly(VAm) fibers had a
diameter of 28 .mu.m and were 5.5 denier (0.61 tex). Curing was
performed in an oven at 80.degree. C. for 30 minutes. The poly(VAm)
fiber absorbed 68.3 g/g (after 1 hour) and 73.5 g/g (after 3 hours)
of 0.1 M hydrochloric acid under no load, and 19.6 g/g (after 1
hour) under a load of 0.28 psi.
[0167] Poly(VAm) fibers also were produced from the identical
spinning solution using a dry-jet wet spinning technique. In this
technique, the spinnerette was positioned above the coagulation
bath and the fiber originally was spun in air, then pulled through
the coagulation bath.
[0168] As illustrated above, the physical properties of poly(AA)
permit dry spinning of the polymer. Poly(AA) has a high extensional
viscosity that allows stringing of the polymer solution and drawing
of filaments, or fibers, from a poly(AA) spinning solution.
Poly(VAm) does not have the physical properties necessary for dry
spinning, and therefore is subjected to a wet spinning process. In
the spinning of an acidic or a basic water-absorbing polymer,
persons skilled in the art can determine whether a dry spinning or
a wet spinning process should be used based on the properties of
the resin.
EXAMPLE 5
Preparation of Twisted Rope Multicomponent SAP Fibers
[0169] A multicomponent SAP fiber of the present invention was
prepared by twisting together a poly(AA) fiber of Example 3 and a
poly(VAm) fiber of Example 4 to provide intimate contact between
the acidic and basic water-absorbing resins. After twisting the
acidic and basic water-absorbing fibers together, the resulting
twisted rope fiber was heated in a 125.degree. C. oven for about 10
to about 20 minutes. Twisted rope fibers containing a 50:50 mole
ratio of poly(AA) of Example 3 and poly(VAm) of Example 4 absorbed
aqueous media as follows:
1 Aqueous AUL.sup.1) (g/g) AUL (g/g) Testing Medium (after 1 hr)
(after 4 hr) Synthetic urine 33.0.sup.4) (20.2).sup.3) 35.7 (26.2)
30.4 36.4 0.9% saline 24.1 (19.6) 25.4 (21.3) 23.9 24.6 Synthetic
blood.sup.2) 29.2 (24.1) 30.0 (26.1) 27.2 28.8 .sup.1)Absorbance
under load of 0.7 psi; .sup.2)PLASMION .RTM., available from
Rhone-Poulenc Rorer Bellon, Neilly sur Seine, Belgium; .sup.3)the
value in parentheses is the amount of aqueous medium absorbed by a
commercial SAP fiber, i.e., OASIS .TM., available from Allied
Colloids, England, and is included for comparative purposes; and
.sup.4)absorption tests were run in duplicate.
[0170] In another example, a twisted fiber containing a 2:1 mole
rate of poly(VAm) fiber to poly(AA) fiber was prepared. This
twisted fiber also exhibited excellent fluid adsorption properties.
In addition, during hydration of the twisted fiber, distinct
entanglement of the fibers was observed.
[0171] In Example 5, the twisted rope was annealed after the fibers
were twisted together. However, annealing of the individual fibers,
prior to braiding, also can be performed, as well as annealing of
the individual fibers followed by annealing of the twisted rope
fiber.
[0172] Although Example 5 is directed to a single fiber of a
poly(AA) and a single fiber of a poly(VAm) twisted together in the
form of a braid, a twisted rope fiber of the present invention also
encompasses embodiments wherein one or more poly(AA) fibers and one
or more poly(VAm) fibers are twisted together in the form of a
braid. Accordingly, embodiments wherein one or a plurality of
(e.g., 1 to 500) poly(AA) fibers twisted together with one or a
plurality of (e.g., 1 to 500) poly(VAm) fibers also are within the
scope of the present invention.
[0173] In the twisted fiber embodiment, the mole ratio of basic
resin to acidic resin is about 5:1 to about 1:5, and preferably
about 3:1 to about 1:3. To achieve the full advantage of the
present invention, the mole ratio is about 2:1 to about 1:2.
[0174] The effect of cure time and cure temperature on absorbency
of a 50:50 mole ratio twisted fiber of Example 5 also was examined.
The results of this test are summarized in Table 1.
2TABLE 1 Effect of cure time and temperature on the absorbency of
twisted fibers Time of cure Temp of AUL.sup.1) (g/g) AUL.sup.1)
(g/g) (mins) cure (.degree. C.) (after 1 hr) (after 3 hr) 30 80
33.08 37.66 10 125 38.41 40.03 20 125 55.46 63.21 30 125 33.53
36.80 120 125 29.28 32.11 .sup.1)amount of synthetic urine absorbed
under a load of 0.7 psi.
[0175] The rate of absorption for the 50:50 mole ratio twisted
fibers of Example 5, cured at 125.degree. C. for 20 minutes, was
compared to OASIS.TM. fibers, poly(VAm) fibers of Example 4, and
poly(AA) fibers of Example 3. The results are summarized in FIG.
10. FIG. 10 shows that the twisted SAP fibers absorb more rapidly
than poly(VAm) and poly(AA) fibers, and over time outperforms
OASIS.TM. fibers.
[0176] A test also was performed to determine whether fiber length
affected absorption. The twisted fiber multicomponent SAP of
Example 5, having a length of 5, 10, 20, and 40 mm, was compared to
poly(AA) granules, OASIS.TM. fibers, and physical blends of
poly(AA) and poly(VAm) fibers having a length 5, 10, 20, and 40 mm
in length, for absorption rate of synthetic urine under 0.28 psi
pressure. Absorption improved with increasing fiber length up to 20
mm, then decreased at 40 mm. The twisted fiber multicomponent SAP
outperformed the blend of poly(AA) and poly(VAm) fibers.
[0177] A multicomponent SAP fiber of the present invention also can
be in the form of a core of a first resin and a sheath, or shell,
of a second resin. This embodiment is illustrated in Examples 6 and
7.
EXAMPLE 6
Preparation of Multicomponent SAP Fibers Having a Poly(AA) Core and
a Poly(VAm) Sheath
[0178] Poly(AA) fibers were prepared as set forth in Example 3. The
poly(AA) fibers then were passed through a solution of poly(VAm)
(10-20% solids like in Example 4). The resulting coated fiber then
was passed through a coagulation bath containing EGDGE (0.5 w/w)
and acetone. The resulting core/sheath multicomponent SAP fibers
were dried and cured in a fan-assisted oven at 60.degree. C. for 1
hour. A typical core/sheath multicomponent SAP fibers contained
about 0.008 g of poly(AA) and 0.011 g of poly(VAm), or a mole ratio
of acrylic acid to vinylamine of 1:2.3. The multicomponent SAP
fiber of Example 6 absorbed 18.2 g/g of synthetic urine after 60
minutes under a 0.7 psi load. In comparison, the poly(AA) fibers of
Example 3 absorbed 8.4 g/g under identical conditions.
EXAMPLE 7
Preparation of Multicomponent SAP Fibers Having a Poly(VAm) Core
and a Poly(AA) Sheath
[0179] An aqueous polyvinylamine solution (10% solids) was combined
with 0.025 mol % of EGDGE crosslinker. The resulting solution was
mixed until homogeneous, and then allowed to crosslink lightly at
40.degree. C. for 20 minutes to form a spinning dope. The dope was
injected directly into a coagulation bath containing EGDGE,
typically in an amount of about 0.25% to about 1% based on a w/w %
concentration. The coagulant in the bath was a nonsolvent for
poly(VAm), typically acetone. The poly(VAm) was spun directly into
the bath at a flow rate of 2.54 cm.sup.3/hr. The fiber was produced
at a fast rate, with coagulation occurring initially from the
outside. The process started with the production of a skin. This
type of coagulation produced a fiber morphology having voids within
the core, as illustrated in FIGS. 11-13. The fiber was drawn
through the bath, and upwards from the bath. On drawing the fiber
from the coagulation bath, it was passed over an acetone soaked
roller and then passed into a coating bath containing poly(AA) and
EGDGE. This bath contained a concentrated aqueous solution of
poly(AA) (50-70 w/w %) diluted to about 15% w/w % polyacrylic acid
with a polar solvent, typically acetone. The EGDGE was present at
about 0.5 mol %. Passing the fiber through this bath coated the
core of poly(VAm) with a sheath of poly(AA). After passing through
this bath, the fiber was passed over a second acetone-coated roller
and into a doping bath containing 5 wt % triethylamine in acetone.
After passing the fiber through this solution, the fiber was wound
at a speed of about 50-60 rpm. The fibers thus produced were
removed from the roller and cured for 30 minutes at 125.degree. C.
The multicomponent SAP fibers were 25 denier (2.8 tex). Increasing
the cure time of the fibers at 125.degree. C. up to 60 minutes or
longer, resulted in a change in the morphology of the hydrated
fibers. The hydrated fiber gel was harder than hydrated fibers
cured for only 20 to 30 minutes. Upon removal of the fibers from
the AUL test cell, the structure fell apart and no longer resembled
a mat.
[0180] The multicomponent SAP fibers of Example 7 were tested for
an ability to absorb artificial urine, artificial blood, and 0.9%
saline. The test results are summarized below.
3 Aqueous AUL (after 1 AUL (after 4 Testing medium hour @ 0.7 psi)
hour @ 0.7 psi) Synthetic urine 24.9 26.0 0.9% saline 19.3 24.4
Synthetic blood 20.5 22.5
[0181] Upon hydration, the fibers of Example 7 formed a mat-type
structure. On completion of the AUL test, the mat maintained its
integrity, and it was possible to remove the mat as one piece. In
contrast, the twisted rope fiber of Example 5 fractured into its
individual fiber components after hydration. Examination of the mat
produced with the core-shell fiber of Example 7 revealed an open
structure with a very fibrous appearance. No free fluid was present
on the surface of the fibers. Accordingly, all of the fluid was
contained within the structure of the fiber. It also was observed
that as the coating of poly(AA) increased, AUL values of 50 g/g
were attained.
[0182] The fibers of Example 7 were tested to determine the effect
of cure time on the absorbency of the fibers under a 0.7 psi load.
Four samples were prepared identically, then subjected to a cure
time of 1, 3, 5, or 20 minutes, each at 125.degree. C. The test
results are summarized in Table 2, showing that an increased curing
time improved the absorption of synthetic urine.
4TABLE 2 Time of cure AUL (g/g) AUL (g/g) (mins) (after 1 hr)
(after 3 hr) 1 16.9 17.6 3 17.6 18.9 5 18.9 20.0 20 29.0 29.5
[0183] The fibers of Example 7 also were prepared using an
alternate procedure wherein poly(VAm) fibers prepared in Example 4
were passed through a solution containing poly(AA), EGDGE (about
0.5 to about 5 mol %), and triethylamine (5 mol %). In different
runs, the fibers were dried and cured either by microwave (720W)
for 4 minutes, or by a fan-assisted oven at 60.degree. C. for 60
minutes. A typical core-sheath SAP fiber contained 0.16 g poly(VAm)
and 0.16 g poly(AA), i.e., a mole ratio of poly(VAm) to poly(AA) of
2:1. This SAP fiber absorbed 26.8 g/g of synthetic urine under a
load of 0.7 psi after 60 minutes. Under the same conditions,
poly(VAm) fibers absorbed 14.2 g/g of synthetic urine.
[0184] The following Examples 8-11 illustrate other embodiments of
the present invention, in particular, embodiments wherein the fiber
comprises microdomains of an acidic resin in a continuous phase of
a basic resin, or vice versa.
EXAMPLE 8
Preparation of a Poly(VAm) Fiber Containing Microdomains of
Poly(AA)
[0185] To a poly(VAm) spinning solution prepared as set forth in
Example 4 was added finely milled poly(AA) fines (<20 .mu.m
diameter). The mixture was stirred until a homogeneous solution was
obtained (about 5 minutes). The spinning solution was spun into an
EGDGE (about 0.5% to about 5% w/w)-acetone coagulation bath as in
Example 4. The resulting fibers were cured in an oven at 60.degree.
C. for 60 minutes.
[0186] A typical multicomponent SAP fiber of Example 8 contained
5.54 g of poly(VAm) and 0.11 g of poly(AA), which is a mole ratio
of poly(VAm) of poly(AA) of 6:1, and 2% w/w amount of EGDGE
crosslinker. These fibers absorbed 24.2 g/g synthetic urine after 1
hour under a load of 0.7 psi. An identical poly(VAm) fiber that is
free of poly(AA) fines, absorbed 12.1 g/g, under identical
conditions.
EXAMPLE 9
Preparation of a Poly(AA) Fiber Containing Microdomains of
Poly(VAm)
[0187] To an aqueous poly(AA) solution prepared as set forth in
Example 3 was added finely milled poly(VAm) fines (<20 .mu.m
diameter). The mixture was stirred until a homogeneous solution was
obtained (about 5 minutes). The spinning solution was dry spun as
described in Example 3. The resulting fibers were cured in an oven
at 60.degree. C. for 60 minutes.
[0188] A typical multicomponent SAP fiber of Example 9 contained
0.13 g of poly(VAm) and 4.94 g of poly(AA), which is a mole ratio
of poly(VAm) to poly(AA) of 1:12, and 0.5% w/w of EGDGE
crosslinker. The fibers of Example 9 absorbed 18.4 g/g of synthetic
urine after 1 hour under a load of 0.7 psi. An identical poly(AA)
fiber that is free of poly(VAm) fines absorbed 8.4 g/g, under
identical conditions.
EXAMPLE 10
[0189] In a method identical to Example 9, VISCOMER.TM. was added
to a solution of poly(VAm). VISCOMER.TM. is a commercially
available poly(AA) from Chemdal Corporation, Palatine, Ill.
VISCOMER.TM. has a molecular weight of about 4 million, and a
particle size of less than 10 .mu.m in diameter. The resulting
spinning solution was spun into an EGDGE (from about 0.5 to about
5% w/w)-acetone coagulation bath as previously described. The
resulting fibers were cured in an oven at 60.degree. C.
overnight.
[0190] A typical multicomponent SAP fiber of Example 10 contained a
mole ratio of poly(VAm) to poly(AA) of 1:1, and 0.5% w/w of EGDGE
crosslinker. The fibers of Example 10 absorbed 14.47 g/g of
synthetic urine under a load 0.7 psi after 60 minutes.
EXAMPLE 11
[0191] In a method identical to Example 9, CARBOPOL.TM. was added
to a solution of poly(VAm). CARBOPOL.TM. is a commercially
available poly(AA) from BF Goodrich Co., Cleveland, Ohio.
CARBOPOL.TM. has a molecular weight of about 400,000 to about
4,000,000, and a particle size of about 2 to about 7 .mu.m in
diameter. The resulting spinning solution was spun into an EGDGE
(about 0.5 to about 5% w/w)-acetone coagulation bath as previously
described. The resulting fibers were cured in an oven at 60.degree.
C. overnight.
[0192] A typical multicomponent SAP particle of Example 10
contained a 1:1 mole ratio of poly(VAm) to poly(AA), and 0.5% w/w
of EGDGE crosslinker. The fibers of Example 11 absorbed 17.5 g/g of
synthetic urine under a load of 0.7 psi after 60 minutes.
[0193] The following Example 12 illustrates an embodiment wherein
poly(VAm) and poly(AA) fibers are coextruded.
EXAMPLE 12
Preparation of Multicomponent SAP Fibers by Coextrusion
[0194] Poly(VAm) fibers were prepared by the wet spinning method
disclosed in Example 4. In parallel, poly(AA) fibers were prepared
by the dry spinning method disclosed in Example 3. The poly(AA)
fibers were passed through a heated chamber at 60.degree. C.,
followed by coextrusion with the poly(VAm) fibers. The coextruded
SAP fibers were cured at 60.degree. C. for 1 hour.
[0195] A typical coextruded multicomponent SAP fiber of the present
invention contains a 1:1 mole ratio of poly(VAm) to poly(AA). The
coextruded fiber absorbed 28.1 g/g of synthetic urine under a load
of 0.7 psi after 60 minutes. In comparison, the poly(AA) fibers of
Example 3 absorbed 8.4 g/g and the poly(VAm) fibers of Example 4
absorbed 12.9 g/g under identical conditions.
[0196] The following Example 13 illustrates surface treating a
multicomponent SAP fiber of the present invention.
EXAMPLE 13
Surface Treating of Multicomponent SAP Fibers
[0197] The twisted rope SAP fibers of Example 5 were passed through
a solution of propylene glycol and water (80:20 w/w) to coat the
twisted fibers. The coated twisted fibers then were dried in a
125.degree. C. oven for 1 hour. The resulting surface crosslinked
SAP fibers had a mole ratio of poly(AA) to poly(VAm) of 1:1, and a
weight ratio of twisted fibers to surface coating of 4.7:1. The
surface crosslinked multicomponent SAP fibers absorbed 10.5 g/g of
synthetic urine under a load of 0.7 psi after 60 minutes.
[0198] The following tables contain absorption and retention data
for the multicomponent SAP fibers of the present invention, for
individual polymers present in the multicomponent SAP fibers, and
for simple admixtures of the dry resins present in the
multicomponent SAP fibers. The data shows a significant improvement
in water absorption and retention for the present multicomponent
SAP fibers containing microdomains of an acidic and/or basic resin
polymers within each particle compared to the individual resins and
a simple admixture of the individual resins. The data in Tables 3-8
shows the improved ability of multicomponent SAP fibers of the
present invention to absorb and retain an aqueous 0.9% saline
solution.
5TABLE 3 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7
psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.)
Poly(DAEA) 9.6 8.1 23.9 13.5 9.3 24.2 alone.sup.1) Polyacrylic Acid
11.9 10.8 14.3 12.0 10.8 14.3 alone.sup.2) SAP-1.sup.3) 11.0 10.9
45.2 14.8 14.4 48.0 SAP-2.sup.4) 12.5 9.6 26.7 18.9 13.1 30.1
SAP-3.sup.5) 12.4 11.3 37.3 16.5 14.7 42.3 SAP-4.sup.6) 20.1 17.2
28.6 24.7 20.7 34.1 SAP-5.sup.7) 25.3 18.2 35.3 28.1 23 38.7
Multicomponent SAP-1.sup.8) 0.sup.9) 23.7 16.3 41.6 26.9 20 41.7
200 26.7 24.7 41.2 27.1 25.1 39.9 400 27.3 24.1 43.4 27.5 24.5 44.0
600 29.2 23.8 41.8 29.5 24.0 41.2 800 26.6 24.1 40.9 26.7 24.2 41.7
1,000 27.5 24.3 39.9 27.8 24.2 40.7 Multicomponent SAP-2.sup.10)
0.sup.9) 26.3 15.4 40 26.9 17.3 39.4 400 26.5 20.5 39.3 27 22.4
40.3 600 27 18.3 40.2 27.1 20.7 40.6 .sup.1)particle size-180-710
.mu.m; .sup.2)0% neutralization, particle size-180-710 .mu.m,
surface crosslinked-600 ppm EGDGE; .sup.3)mixture of 60%
poly(DAEA), particle sizes less than 180 nm, and 40% polyacrylic
acid-0% neutralized; .sup.4)mixture of 60% poly(DAEA), particle
sizes less than 180 nm, and 40% polyacrylic acid-0% neutralized,
crosslinked with 600 ppm EGDGE; .sup.5)mixture of 60% poly(DAEA),
particle size-180-710 .mu.m, and 40% polyacrylic acid-0%
neutralized; .sup.6)mixture of 60% poly(DAEA), particle
size-180-710 .mu.m, and 40% polyacrylic acid-0% neutralized,
crosslinked with 600 ppm EGDGE; .sup.7)mixture of 60% poly(DAEA),
particle sizes less than 180 .mu.m, and 40% polyacrylic acid-20%
neutralized, particle size 180-710 .mu.m; .sup.8)multicomponent SAP
containing microdomains of poly(DAEA) (<180 .mu.m) as dispersed
phase in poly(AA) (DN = 0) continuous phase, poly(DAEA)/poly(AA)
weight ratio-60/40; .sup.9)ppm surface crosslinking with EGDGE; and
.sup.10)multicomponent SAP containing microdomains of poly(DAEA)
(<180 .mu.m) as dispersed phase in poly(AA) (DN = 20) continuous
phase, poly(DAEA)/poly(AA) weight ratio-60/40.
[0199]
6TABLE 4 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7
psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.)
Poly(DMAPMA).sup.11) 10.2 8.6 18 11.4 10 18.3 Poly(DMAPMA).sup.12)
9.3 5.2 17.4 11 6.9 17.8 Polyacrylic acid.sup.13) 11.9 10.8 14.3
12.0 10.8 14.3 SAP-6.sup.14) 14.5 10.9 18.8 17.2 14.3 20.9
SAP-7.sup.15) 14 12 38.7 17.9 15.7 43.6 SAP-8.sup.16) 12.5 10.4
24.8 14.5 12.4 24.8 Multicomponent SAP-3.sup.17) 0.sup.9) 28.8 15
41.6 31 17.5 41.5 100 27.4 24.2 38.8 27.1 23.6 38.8 200 27.3 24.2
39.8 25.8 23 39 400 26 23 37 25.2 22.5 36.4 600 25.1 22.3 37.1 24.7
21.3 36.1 Multicomponent SAP-4.sup.18) 0.sup.9) 31.9 11.6 44.2 31.8
15.7 44.9 200 27.6 24.3 37.8 27.5 23.4 38.1 400 27.5 23.7 37.4 27.2
23.1 38.8 Multicomponent SAP-5.sup.19) 0.sup.20) 23.6 12.9 37.9 25
14.4 38.5 1500 24.7 16.9 36.4 25.5 18.3 37.5 .sup.11)Poly(DMAPMA),
particle size less than 106 .mu.m; .sup.12)Poly(DMAPMA), particle
size 106-180 .mu.m; .sup.13)Polyacylic acid, particle size-180-710
.mu.m-0% neutralized, surface crosslinked with 600 ppm EGDGE;
.sup.14)mixture of 60% poly(DMAPMA), particle size 106-180 .mu.m,
and 40% polyacrylic acid-0% neutralized; .sup.15)mixture of 60%
poly(DMAPMA), particle size <106 .mu.m, and 40% polyacrylic
acid-0% neutralized; .sup.16)mixture of 50% poly(DMAPMA), and 50%
polyacrylic acid-0% neutralized; .sup.17)multicomponent SAP
containing microdomains of poly(DMAPMA) (<106 .mu.m) as
dispersed phase in poly(AA) (DN = 0) continuous phase,
poly(DMAPMA)/poly(AA) weight ratio 60/40; .sup.18)multicomponent
SAP containing microdomains of poly(DMAPMA) (106-180 .mu.m) as
dispersed phase in poly(AA) (DN = 0) continuous phase,
poly(DMAPMA)/poly(AA) weight ratio 60/40. .sup.19)multicomponent
SAP containing microdomains of poly(AA) (DN = 0%) (<106 .mu.m)
as dispersed phase in poly(DMAPMA) continuous phase,
poly(AA)/poly(DMAPMA) weight ratio 50/50; and .sup.20)ppm surface
crosslinking with dibromooctane.
[0200]
7TABLE 5 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7
psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.)
Poly(vinylamine) 14.2 14.4 21.4 15 14.3 23.4 alone SAP-9.sup.21)
21.2 18.6 28.3 23.8 20.5 36.3 Multicomponent SAP-6.sup.22) 0.sup.9)
14.9 12.8 53.8 16.9 15.6 55.4 100 37.5 30.1 45.5 37.5 30.1 45.5 200
36.2 30.4 48.5 35.9 30.2 47.4 400 34.6 30.6 44.9 34.6 30.6 46.2
.sup.21)mixture of 37% poly(vinylamine) and 63% poly(AA); and
.sup.22)multicomponent SAP containing microdomains of
poly(vinylamine) (<180 .mu.m) as dispersed phase in poly(AA) (DN
= 0) continuous phase, poly(vinylamine)/poly(AA) weight
ratio-37/63.
[0201]
8TABLE 6 Coextruded Multicomponent SAP Particle (60/40 weight ratio
poly(DAEA)/poly(AA) AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL
psi, (0.7 psi, AUNL Surface Treatment 1 hr.) 1 hr.) (1 hr.) 3 hr.)
3 hr.) (3 hr.) 0 30.5 13.3 41.1 30.6 16.3 40.2 200 ppm EGDGE 31
27.7 40.2 30.8 27.3 39.9
[0202]
9TABLE 7 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7
psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.)
Poly(vinyl- 21 16.1 31.2 22.4 18.0 32.7 quanidine) hydro- chloride
alone Multicomponent SAP-7.sup.23) 0.sup.9) 18.8 12.7 40.6 21.2
15.3 46.8 200 22 19.2 33.5 23.5 20.3 37.4 .sup.23)multicomponent
SAP containing microdomains of poly(VG) and poly(AA), with a
poly(VG)/poly(AA) weight ratio-50/50.
[0203]
10TABLE 8 Coextruded Multicomponent SAP Particle (37.4/62.6 weight
ratio PEI/poly(AA)) Cross- AUL (0.28 AUL (0.7 AUL (0.28 AUL (0.7
PEI Gel linker psi, psi, AUNL (1 psi, psi, AUNL (3 (% Solids)
Level.sup.24) 1 hr.) 1 hr.) hr.) 3 hr.) 3 hr.) hr.) 20 1.0 23 19.5
32 24.3 20.8 34.9 10 1.5 20.1 16.2 28.4 22.4 18.1 31.9 .sup.24)mole
% EGDGE.
[0204] To demonstrate that a multicomponent SAP fiber of the
present invention can contain an acidic resin and/or a basic resin
that is partially neutralized, a series of tests was performed on
multicomponent SAP particles containing 45% by weight poly(AA) and
55% by weight poly(vinylamine). The multicomponent SAP particles
were prepared in an identical manner, but the percent
neutralization of the poly(AA) and poly(vinylamine) was changed.
The various multicomponent SAP particles were tested for an ability
to absorb and retain synthetic urine, and the results are
summarized in Table 9.
11TABLE 9 % Neutralized Poly(vinylamine)/ AUL AUL % Neutralized
Surface (0.7 psi, (0.7 psi, Poly(AA) (by weight) Crosslinking 1 hr)
3 hr) 0/0 None 16.8 21.6 0/10 None 13.4 16.9 0/25 None 12.6 16 10/0
None 37.2 37.7 25/0 None 24.4 25.3 10/10 None 19.2 24.3 25/25 None
19.8 19.3 50/50 None 11.9 13.8 0/0 PG/H.sub.2O .sup.1) 43.3 47.6
0/10 PG/H.sub.2O 34 36.9 0/25 PG/H.sub.2O 14.4 17.4 10/0
PG/H.sub.2O 30.9 31.4 25/0 PG/H.sub.2O 24.1 25.3 10/10 PG/H.sub.2O
39.3 41.2 25/25 PG/H.sub.2O 18.9 18.7 50/50 PG/H.sub.2O 12.1 14.5
.sup.1) Surface treatment with propylene glycol/water (80/20
ratio), dried at 125.degree. C. for 2.5 hours.
[0205] In another series of tests, the ratio of acidic
water-absorbing resin to basic water-absorbing resin in the
multicomponent SAP particles was varied. In particular, Table 10
summarizes the AUNL data and the AUL data at different pressures
for a series of multicomponent SAP particles containing
poly(vinylamine) and poly(AA) over the range of 25% to 75% by
weight. The multicomponent SAP particles used in this series of
tests were multicomponent SAP particles containing 55% by weight
poly(vinylamine) and 45% by weight poly(acrylic acid). All
multicomponent SAP particles used in the test were
surface-crosslinked with 50 ppm EGDGE. The multicomponent SAP
particles were tested for an ability to absorb and retain synthetic
urine.
12TABLE 10 Weight Ratio AUL AUL AUL AUL AUL AUL AUL Poly (vinyl
0.28 0.7 1.4 0.28 0.7 1.4 0.28 AUL AUL amine)/- psi psi psi AUNL
psi psi psi AUNL psi 0.7 psi 1.4 psi AUNL Poly(AA) (1 hr) (1 hr) (1
hr) (1 hr) (3 hr) (3 hr) (3 hr) (3 hr) (17 hr) (17 hr) (17 hr) (17
hr) 25/75 41.3 36.6 53.6 41.2 36.6 54 39.1 33.3 52.3 30/70 46.3
42.2 58.7 46.4 42.8 59.6 43.1 38.7 58.4 35/65 43.6 38.5 54.4 44.2
39.5 54.8 42 35.8 54.3 40/60 52.1 44.3 63.9 53.7 46.5 66.7 51.7
43.2 65.2 45/55 50.4 46 61.1 51.4 47.4 63.2 47.3 41.9 61.9 50/50
52.2 45 26 62.5 54.8 47.7 29 66.7 52.8 45.4 30.9 66.4 55/45 52.1
47.3 27.4 62.5 54.8 49.3 31.3 66.2 53.1 44.8 32.5 65.4 60/40 52.8
47 27.8 64.6 55.2 49.6 30.9 68 52.6 44 33 67.6 65/35 50 45.9 59.2
51.6 47.3 61.8 48.8 41 61.4 70/30 47.5 43.1 57.4 48.3 43.8 59.4
43.5 37.2 56.7 75/25 43.9 39.3 53.6 43.9 39.2 54.8 38.9 31.2
51.4
[0206] In addition to an ability to absorb and retain relatively
large amounts of a liquid, it also is important for an SAP to
exhibit good permeability, and, therefore, rapidly absorb the
liquid. Therefore, in addition to absorbent capacity, or gel
volume, useful SAP fibers also have a high gel strength, i.e., the
fibers do not deform after absorbing a liquid. In addition, the
permeability or flow conductivity of a hydrogel formed when SAP
fibers swell, or have already swelled, in the presence of a liquid
is extremely important property for practical use of the SAP
fibers. Differences in permeability or flow conductivity of the
absorbent polymer can directly impact on the ability of an
absorbent article to acquire and distribute body fluids.
[0207] Many types of SAP particles exhibit gel blocking. "Gel
blocking" occurs when the SAP particles are wetted and swell, which
inhibits fluid transmission to the interior of the SAP particles
and between absorbent SAP particles. Wetting of the interior of the
SAP particles or the absorbent structure as a whole, therefore,
takes place via a very slow diffusion process, possibly requiring
up to 16 hours for complete fluid absorption. In practical terms,
this means that acquisition of a fluid by the SAP particles, and,
accordingly, the absorbent structure, such as a diaper, can be much
slower than the rate at which fluids are discharged, especially in
gush situations. Leakage from an absorbent structure, therefore,
can occur well before the SAP particles in the absorbent structure
are fully saturated, or before the fluid can diffuse or wick past
the "gel blocked" particles into the remainder of the absorbent
structure. Gel blocking can be a particularly acute problem if the
SAP particles lack adequate gel strength, and deform or spread
under stress after the SAP particles swell with absorbed fluid.
[0208] Accordingly, an SAP particle can have a satisfactory AUL
value, but will have inadequate permeability or flow conductivity
to be useful at high concentrations in absorbent structures. In
order to have a high AUL value, it is only necessary that the
hydrogel formed from the SAP particles has a minimal permeability
such that, under a confining pressure of 0.3 psi, gel blocking does
not occur to any significant degree. The degree of permeability
needed to simply avoid gel blocking is much less than the
permeability needed to provide good fluid transport properties.
Accordingly, SAPs that avoid gel blocking and have a satisfactory
AUL value can still be greatly deficient in these other fluid
handling properties.
[0209] Accordingly, an important characteristic of the
multicomponent SAP fibers of the present invention is permeability
when swollen with a liquid to form a hydrogel zone or layer, as
defined by the Saline Flow Conductivity (SFC) value of the SAP
particles. SFC measures the ability of an SAP to transport saline
fluids, such as the ability of the hydrogel layer formed from the
swollen SAP to transport body fluids. A material having relatively
high SFC value is an air-laid web of woodpulp fibers. Typically, an
air-laid web of pulp fibers (e.g., having a density of 0.15 g/cc)
exhibits an SFC value of about 200.times.10.sup.-7 cm.sup.3 sec/g.
In contrast, typical hydrogel-forming SAPs exhibit SFC values of
1.times.10.sup.-7 cm.sup.3 sec/g or less. When an SAP is present at
high concentrations in an absorbent structure, and then swells to
form a hydrogel under usage pressures, the boundaries of the
hydrogel come into contact, and interstitial voids in this high SAP
concentration region become generally bounded by hydrogel. When
this occurs, the permeability or saline flow conductivity
properties in this region is generally indicative of the
permeability or saline flow conductivity properties of a hydrogel
zone formed from the SAP alone. Increasing the permeability of
these swollen high concentration regions to levels that approach or
even exceed conventional acquisition/distribution materials, such
as wood pulp fluff, can provide superior fluid handling properties
for the absorbent structure, thus decreasing incidents of leakage,
especially at high fluid loadings.
[0210] Accordingly, it would be highly desirable to provide SAP
particles having an SFC value that approaches or exceeds the SFC
value of an air-laid web of wood pulp fibers. This is particularly
true if high, localized concentrations of SAP particles are to be
effectively used in an absorbent structure. High SFC values also
indicate an ability of the resultant hydrogel to absorb and retain
body fluids under normal usage conditions.
[0211] The SFC value of the present multicomponent SAP particles
are substantially improved over the SFC value for a standard
poly(AA) SAP, as illustrated in the data summarized in Table 11. A
method for determining the SFC value of SAP particles is set forth
in Goldman et al. U.S. Pat. No. 5,599,335, incorporated herein by
reference.
13TABLE 11 Sample 1 Sample 2 (Control).sup.1) (Comparative).sup.2)
Sample 3.sup.3) Sample 4.sup.4) Sample 5.sup.5) Sample 6.sup.6)
Sample 7.sup.7) Time AUL AUL AUL AUL AUL AUL AUL (min) 0.7 psi 0.7
psi 0.7 psi 0.7 psi 0.7 psi 0.7 psi 0.7 psi 0 0 0 0 0 0 0 0 5 25.3
14.8 26 26.3 17.8 19.3 13.6 10 30.7 20.9 33.2 34.5 23.4 20.4 16.2
15 32.1 25.1 37.9 38.8 26.3 21 17.4 30 33.8 31.2 43.3 44.1 29.9
20.8 17.6 45 34.2 34.3 45.8 45.6 31.8 21.6 19.3 60 34.5 36.4 47.6
46.2 32.4 21.7 20.1 120 35.2 40 49.1 47.6 33.6 22.3 20.5 180 35.2
42.3 49.7 48 35.6 22.8 21.7 SFC.sup.8) 15 115 368 685 707 534 930
.sup.1)Standard, commercial SAP, i.e., neutralized poly(AA), 75%
DN, available as A2300, from Chemdal, Corp., Palatine, IL;
.sup.2)Comparative sample containing a dry blend of 55% by weight
unneutralized poly(vinylamine) particles and 45% by weight
unneutralized poly(AA) particles; .sup.3)Multicomponent SAP
particles, containing 55% unneutralized poly(vinylamine) and 55%
poly(AA), prepared in a KitchenAid mixer; .sup.4)Multicomponent SAP
particles, containing 55% unneutralized poly(vinylamine) and 45%
poly(AA); .sup.5)Multicomponent SAP particles, containing 55%
unneutralized poly(vinylamine) and 45% poly(AA) as a core-shell
granule; .sup.6)Multicomponent SAP particles, containing 55%
unneutralized poly(vinylamine) and 45% poly(AA)as an
interpenetrating polymer network; .sup.7)Multicomponent SAP
particles, containing 55% unneutralized poly(vinylamine) and 45%
poly(AA) as layers; and .sup.8)in .times. 10.sup.-7
cm.sup.3sec/g.
[0212] The data summarized in Table 11 shows a substantial
improvement in AUL at 0.7 psi and SFC for multicomponent SAP
particles in comparison to a control SAP and a comparative dry
blend of SAP particles. Accordingly, a present multicomponent SAP
fiber has an SFC value of at least about 150.times.10.sup.-7
cm.sup.3 sec/g, and preferably at least about 250.times.10.sup.-7
cm.sup.3 sec/g. To achieve the full advantage of the present
invention, the SFC value is at least about 350.times.10.sup.-7
cm.sup.3 sec/g, and can range to greater than 1000.times.10.sup.-7
cm.sup.3 sec/g.
[0213] The present multicomponent SAP particles also exhibit
excellent diffusion of a liquid through and between the particles.
Diffusion is measured in a PUP capacity test, which is similar to
the AUL test, but the SAP particles are allowed to absorb a fluid
on demand. The PUP test is designed to illustrate absorption
kinetics of an SAP particle. It is expected that a multicomponent
SAP fiber of the present invention has an initial PUP capacity rate
of at least 50 g/g/hr.sup.1/2, and preferably at least 70
g/g/hr.sup.1/2. To achieve the full advantage of the present
invention, the multicomponent SAP fibers have an initial PUP
capacity rate of greater than 90 g/g/hr.sup.1/2, and preferably
greater than 100 g/g/hr.sup.1/2.
[0214] In another test, the free swell rate (FSR) of a present
multicomponent SAP particle was compared to the FSR of a standard
poly(AA) SAP and 55/45 weight ratio of
poly(vinylamine)/poly(acrylic acid) dry particle blend. The FSR
test, also known as a lockup test, is well known to persons skilled
in the art.
[0215] The present multicomponent SAP particles had an FSR (in
g/g/sec) of 0.49 and 0.48, for 55/45 weight ratio multicomponent
SAP particles made in a KitchenAid mixer and a Brabender extruder,
respectively. In comparison, a dry blend had an FSR of 0.10 and a
standard neutralized poly(AA) had an FSR or 0.32. Multicomponent
SAP particles of the present invention, therefore, have an FSR of
greater than 0.35, preferably greater than 0.40, and most
preferably greater than 0.45. These data further show the improved
ability of the present SAP particles to absorb and retain larger
amounts of an electrolyte-containing liquid quickly.
[0216] The multicomponent SAP fibers also can be mixed with
particles of a second water-absorbing resin to provide an SAP
material having improved absorption properties. The second
water-absorbing resin can be an acidic water-absorbing resin, a
basic water-absorbing resin, or a mixture thereof. The SAP material
comprises about 10% to about 90%, and preferably about 25% to about
85%, by weight, multicomponent SAP fibers and about 10% to about
90%, and preferably, about 25% to about 85%, by weight, particles
of the second water-absorbing resin. More preferably, the SAP
material contains about 30% to about 75%, by weight, multicomponent
SAP fibers. To achieve the full advantage of the present invention,
the SAP material contains about 35% to about 75%, by weight, the
multicomponent SAP fibers.
[0217] The second water-absorbing resin can be any of the
previously discussed acidic resins used in the preparation of a
multicomponent SAP. The second water-absorbing resin, either acidic
or basic, can be unneutralized (DN=0), partially neutralized
(O<DN<100), or completely neutralized (DN=100). A preferred
acidic water-absorbing resin used as the second resin is
polyacrylic acid, preferably partially neutralized polyacrylic
acid, e.g., DN about 50%, and preferably about 70% up to about
100%. The second water-absorbing resin also can be any of the
previously discussed basic resins used in the preparation of a
multicomponent SAP. Preferred basic water-absorbing resins used as
the second resin are poly(vinylamine) or a
poly(dialkylaminoalkyl(meth)acryla- mide. Blends of acidic resins,
or blends of basic resins, can be used as the second
water-absorbing resin. Blends of an acidic resin and a basic resin
also can be used as the second water-absorbing resin.
[0218] To illustrate the improved absorption properties
demonstrated by an SAP material comprising multicomponent SAP
particles and particles of a second water-absorbing resin, mixtures
of multicomponent SAP particles and partially neutralized (DN=70)
polyacrylic acid (poly(AA)) particles were prepared. As used here
and throughout the specification poly(AA) (DN=70) refers to a
standard, commercial poly(AA) neutralized about 70% to about 80%,
and poly(AA) (DN=0) refers to unneutralized poly(AA). The
multicomponent SAP particles contain microdomains of
poly(vinylamine) dispersed in poly(AA) (DN=0). The
poly(vinylamine)/poly(AA) weight ratio of the multicomponent SAP
particles was 55/45. The resulting SAP material was tested for an
ability to absorb synthetic urine under load at 0.7 psi, in
accordance with the previously described method. The results are
summarized below:
14 AUL 0.7 psi AUL 0.7 psi SFC (.times.10.sup.-7 wt ratio .sup.1)
(1 hr.) (3 hr.) cm.sup.3 sec/g) 100/0 26.7 27.1 14 75/25 30.2 30.7
26 50/50 36.7 37.7 72 25/75 40.8 42.6 189 0/100 43.0 46.4 787
.sup.1) weight ratio of partially neutralized poly(AA) particles to
multicomponent SAP particles.
[0219] The data presented above shows a substantial improvement in
absorption properties achieved by an SAP material comprising a
blend of multicomponent SAP particles and particles of a second
water-absorbing resin over conventional, partially neutralized
poly(AA).
[0220] The following Examples 14-17 show SAP materials containing
present multicomponent SAP fibers and a second water-absorbing
resin.
EXAMPLE 14
[0221] The core-sheath multicomponent SAP fibers of Examples 6 and
7, individually, were admixed with a commercial SAP, i.e.,
ASAP2300.TM. granules, a 75%-80% neutralized poly(AA) available
from Chemdal Corp., Palatine, Ill., until a homogeneous mixture
resulted. The resulting mixtures were about 50:50 (w/w) of fibers
of Examples 6 or 7 and ASAP2300.TM..
[0222] A typical mixture contained 0.052 g of fiber of Example 6
and 0.050 g of ASAP2300.TM.. The SAP material of Example 14
absorbed 29.7 g/g of synthetic urine after 1 hour under a load of
0.7 psi. In comparison, the fibers of Example 6 absorbed 18.2 g/g
and ASAP2300.TM. absorbed 34.0 g/g, under the identical
conditions.
EXAMPLE 15
[0223] Similar to Example 14, the fibers of Examples 6 and 7,
individually, were admixed with OASIS.TM. fibers. A typical
formulation contained 0.051 g of fibers of Example 7 and 0.050 g of
OASIS.TM., i.e., a 50:50 (w/w) ratio. The SAP material of Example
15 absorbed 20.1 g/g of synthetic urine after 1 hour under a load
of 0.7 psi. In comparison, the OASIS.TM. fibers absorbed 18.9 g/g
and the fibers of Example 7 absorbed 26.8 g/g.
EXAMPLE 16
[0224] Similar to Examples 14 and 15, the coextruded fibers of
Example 12 were admixed with ASAP2300.TM., i.e., a 50:50 (w/w)
ratio. The SAP material of Example 16 absorbed 24.9 g/g of
synthetic urine after 1 hour under a load of 0.7 psi. In
comparison, the fibers of Example 12 absorbed 28.1 g/g and the
ASAP2300.TM. granules absorbed 34.0 g/g, under identical
conditions.
EXAMPLE 17
[0225] Similar to Examples 14-16, the coextruded fibers of Example
12 were admixed with OASIS.TM. fibers. A typical formulation
contained 0.05 g of the fibers of Example 12 and 0.051 g of
OASIS.TM. fibers, i.e., a 50:50 (w/w) ratio. The SAP material of
Example 17 absorbed 16.0 g/g of synthetic urine after 1 hour under
a load of 0.7 psi. In comparison, the fibers of Example 12 absorbed
28.1 g/g and the OASIS.TM. fibers absorbed 18.9 g/g, under
identical conditions.
EXAMPLE 18
[0226] Similar to Examples 14-17, the twisted rope SAP fibers of
Example 5 were admixed with ASAP2300.TM. granules. A typical
formulation contained 0.07 g of the twisted rope SAP fibers and
0.11 g of ASAP2300.TM., i.e., a 40:60 (w/w) ratio. The SAP material
of Example 18 absorbed 21.8 g/g of synthetic urine after 1 hour
under a load of 0.7 psi. In comparison, the twisted rope SAP fibers
of Example 5 absorbed 16.9 g/g and ASAP2300.TM. absorbed 34.0 g/g
under identical conditions.
EXAMPLE 19
[0227] Similar to Examples 14-18, the twisted rope SAP fibers of
Example 5 were admixed with OASIS.TM. fibers. A typical formulation
contained 0.070 g of the twisted rope fibers and 0.067 g of the
OASIS.TM. fibers, i.e., a 50:50 (w/w) ratio. The SAP material of
Example 19 absorbed 14.4 g/g of synthetic urine after 1 hour under
a load of 0.7 psi. In comparison, the twisted rope fibers of
Example 5 absorbed 16.9 g/g and the OASIS.TM. fibers absorbed 18.9
g/g, under identical conditions.
EXAMPLE 20
Mixed Bed Fiber
[0228] A 50:50 mixture, by weight, of poly(acrylic acid) fibers and
poly(vinylamine) fibers was prepared by admixing the fibers. The
poly(AA) and poly(VAm) fibers were produced as described in
Examples 3 and 4, respectively, and were in the uncured state. The
fiber mixture then was passed through a circular core former, which
directs the fiber mixture through a sieve and collects the fiber
mixture on paper, while under a vacuum, to form a mat. The mat thus
formed then was cured, or annealed, for 60 minutes at 125.degree.
C. The cured mat was tested for absorbency under a 0.7 psi load,
and absorbed 37.6 g/g of synthetic urine after 1 hour and 42 g/g
after 4 hours.
[0229] In an alternative route, the poly(AA) and poly(VAm) fibers
were cured first, either prior to admixing or after admixing, and
then the cured fibers were passed through a core former as above.
After a final cure of 60 minutes at 125.degree. C., the fiber mat
absorbed 32.9 g/g (of synthetic urine) after 1 hour and 35.3 g/g
after 4 hours in an AUL test (under 0.7 psi).
[0230] The hydrated mats of Example 20 had very good structural
integrity and retained their shape after being removed from the AUL
sample pot. The surface of the mat was relatively dry. The hydrated
mats did not disintegrate and did not sag to an appreciable
degree.
[0231] To further demonstrate the improved absorption properties of
the present multicomponent SAP fibers, or an SAP material
containing the present SAP fibers, the multicomponent SAP fibers
and SAP materials were compared to physical blends of fibers and
physical blends of a fiber and a granule. The comparative physical
blends did not contain multicomponent SAP fibers of the present
invention. The following Table 12 summarizes the results of
comparative tests on twenty samples, including fibers and SAP
materials of the present invention and comparative samples. The
tested samples have the following compositions:
15 Test Sample Composition 1 Physical mix.sup.1) of amine fibers of
Example 4 and acid fibers of Example 3 (comparative) 2 Physical mix
of amine fibers of Example 4 and poly(AA) granules of Example 1
(comparative) 3 Physical mix of amine granules of Example 2 and
acid fibers of Example 3 (comparative) 4 Multicomponent SAP fiber
of Example 5 5 Physical mix of Test Sample 1 and OASIS .TM. fibers
(comparative) 6 Physical mix of Test Sample 1 and ASAP2300 .TM.
granules (comparative) 7 Physical mix of amine fibers of Example 4
and reprotonated OASIS .TM. fibers (comparative) 8 Poly(VAm)
granules of Example 2 blended with reprotonated OASIS .TM. fibers
(comparative) 9 SAP material of Example 14 10 SAP material of
Example 15 11 SAP material of Example 16 12 SAP material of Example
17 13 Multicomponent SAP fibers of Example 6 14 Multicomponent SAP
fibers of Example 7 15 Multicomponent SAP fibers of Example 12 16
Multicomponent SAP fibers of Example 9 17 Multicomponent SAP fibers
of Example 8 18 Multicomponent SAP fibers of Example 10 19
Multicomponent SAP fibers of Example 11 20 Multicomponent SAP
fibers of Example 13 .sup.1)All blends were prepared by admixing
the solid, dry ingredient until homogeneous; and .sup.2)OASIS .TM.
fibers were reprotonated by wetting the fibers with concentrated
phosphoric acid. The reprotonated fibers were separated from the
acid, then washed with methanol until the methanol filtrate had a
constant pH. The reprotonated fibers then were dried at 60.degree.
C.
[0232]
16TABLE 12 Sample.sup.1) 1 Absorption under 0.7 psi load for 2:1
mix - 14.1 g/g (1 hour) 2 Absorption under 0.7 psi load for 2:1 mix
- 20.6 g/g (1 hour) 3 Absorption under 0.7 psi load for 1:1 mix -
32.0 g/g (1 hour) 4 Absorption under 0.7 psi load for 2:1 mix -
13.7 g/g (1 hour) 5 Absorption under 0.7 psi load for 1:1 mix -
14.3 g/g (1 hour) 6 Absorption under 0.7 psi load for 1:1 MIX -
21.8 g/g (1 hour) 7 Absorption after 1 hour under a 0.7 psi load
was 5 g/g fiber/fiber. There was no increase after 3 hours. 8
Absorption after 1 hour under 0.7 psi was 10.6 g/g, increasing to
17.5 g/g after 3 hours. 9 Absorption after 1 hour under 0.7 psi was
29.6 g/g, increasing to 31.7 g/g after 3 hours. 10 Absorption after
1 hour under 0.7 psi was 20.1 g/g, increasing to 22.5 g/g after 3
hours. 11 Absorption after 1 hour under 0.7 psi was 24.8 g/g,
increasing to 27.7 g/g after 3 hours. 12 Absorption after 1 hour
under 0.7 psi was 16.0 g/g, increasing to 19.8 g/g after 3 hours.
13 Absorption after 3 hours under 0.7 psi was 21.8 g/g. 0 load = 33
g/g after 3 hours. 14 Absorption after 3 hours under 0.7 psi was
32.8 g/g. 0 load = 28.8 g/g after 3 hours. 15 Absorption after 1
hour under 0.7 psi was 28.1 g/g, increasing to 38.7 g/g after 3
hours. 16 Absorption after 3 hours under 0.7 psi was 22.5 g/g. 0
load = 44.6 g/g after 3 hours. 17 Absorption after 3 hours under
0.7 psi was 24.4 g/g. 0 load = 23.1 g/g after 3 hours. 18
Absorption after 3 hours under 0.7 psi was 16.34 g/g. 0 psi = 9.12
g/g. 19 Absorption after 3 hours under 0.7 psi was 22.74 g/g. 0 psi
= 20.37 g/g. 20 Absorption after 1 hour under 0.7 psi was 10.4 g/g,
increasing to 14.2 g/g after 3 hours. .sup.1)for composition, a
poly(VAm) fiber absorbs 14.2 g/g and a poly(AA) fiber absorbs 7.7
g/g.
[0233] A present SAP material has an SFC of greater than
15.times.10.sup.-7 cm.sup.3 sec/g, and typically greater than
20.times.10.sup.-7 cm.sup.3 sec/g. Preferred embodiments have an
SFC about 30.times.10.sup.-7 cm.sup.3 sec/g or greater, for
example, up to about 800.times.10.sup.-7 cm.sup.3 sec/g. In
particular, an SAP material containing 25% multicomponent SAP
particle and 75% poly(AA)(DN=70) particles has an SFC of 34.4
cm.sup.3 sec/g. A present SAP material also demonstrates an
improved initial PUP capacity rate of 45.5 g/g 1 hr.sup.1/2 for the
superabsorbent material. A standard poly(AA) (DN=70) has an initial
PUP capacity rate of 40.7 g/g 1 hr.sup.1/2.
[0234] In particular, multicomponent SAP fibers of Example 7 were
tested for permeability using the SFC test. Analysis was performed
on a 0.1 g test sample under an applied load of 0.3 psi. For
synthetic urine, the fibers of Example 7 exhibited an SFC of
603.times.10.sup.-7 cm.sup.3 sec/g. Similarly, for 0.9% saline and
artificial blood, the fibers of Example 7 exhibited an SFC of 32
and 4.8 cm.sup.3 sec/g, respectively.
[0235] The present multicomponent SAP fibers and superabsorbent
materials containing multicomponent SAP fibers, (a) have an
improved ability to absorb liquids faster, (b) have a better liquid
diffusion rate, and (c) have an improved ability to absorb and
retain liquids. The present SAP fibers and SAP materials,
therefore, are useful in disposable diapers, adult incontinence
products, and catamenial devices, for example.
[0236] In particular, present day diapers generally consist of a
topsheet made from a nonwoven material that is in contact with the
skin of the wearer, an acquisition layer below (i.e., opposite the
skin of wearer) the topsheet, a core that is below the acquisition
layer, and a backsheet below the core. This construction is well
known in the industry. The improvements provided by present
multicomponent SAP fibers, or superabsorbent material, may permit
an acquisition layer to be omitted from a disposable diaper.
[0237] In addition, additional test samples, similar to Example 20,
were prepared and tested for an ability to absorb synthetic urine.
The mixed bed fiber mats contained a weight ratio of either 60/40,
50/50, or 30/70 poly(vinylamine) to poly(acrylic acid), and were
prepared identically as set forth above in Example 20. The mixed
bed fiber mats were annealed at 125.degree. C. for a time period
ranging from 10 to 60 minutes. The ability of the mixed bed fibers
to absorb synthetic urine is summarized in Table 13.
17TABLE 13 Weight Ratio of Cure Condi- AUL Load 1 hr 4 hr PVAm to
PAA Fibers tions (psi) (g/g) (g/g) 50/50 125.degree. C. 10 mins 0
68.71 65.20 0.28 34.64 46.28 0.7 32.96 45.13 125.degree. C. 20 mins
0 73.57 68.40 0.28 46.68 56.43 0.7 37.59 44.35 125.degree. C. 30
mins 0 66.73 66.35 0.28 40.25 37.20 0.7 36.81 39.16 125.degree. C.
45 mins 0 62.29 59.03 0.28 41.83 39.60 0.7 31.41 36.75 125.degree.
C. 60 mins 0 66.53 61.97 0.28 43.54 47.22 0.7 36.05 37.39 30/70
125.degree. C. 10 mins 0 53.82 47.51 0.28 41.23 48.77 0.7 27.48
39.10 125.degree. C. 20 mins 0 56.19 50.67 0.28 34.77 42.56 0.7
32.31 40.03 125.degree. C. 30 mins 0 51.85 43.58 0.28 34.24 32.73
0.7 27.39 32.00 125.degree. C. 45 mins 0 49.77 45.10 0.28 37.34
44.00 0.7 32.31 31.58 125.degree. C. 60 mins 0 48.75 42.39 0.28
34.34 36.47 0.7 52.59 57.73 60/40 125.degree. C. 10 mins 0.7 30.12
34.59 125.degree. C. 20 mins 0.7 37.52 36.81 125.degree. C. 30 mins
0.7 34.74 35.04 125.degree. C. 45 mins 0.7 33.76 34.57 125.degree.
C. 60 mins 0.7 35.96 38.25
[0238] The mixed fibers of Example 20, and the mixed bed fibers
tested in Table 13, showed excellent structural integrity after
hydration by synthetic urine, i.e., the mat of mixed bed fibers can
be lifted without disintegrating.
[0239] In addition, a significant improvement in liquid absorption,
both with respect to kinetics and retention, are expected if the
standard poly(AA)(DN=70) presently used in diaper cores is
completely replaced by multicomponent SAP fibers, or is replaced by
a superabsorbent material of the present invention, i.e., a
composition containing multicomponent SAP fibers and a second
water-absorbing resin, such as poly(AA)(DN=70).
[0240] The improved results demonstrated by the present invention
also permit the thickness of the diaper core to be reduced.
Typically, cores contain 50% or more fluff or pulp to achieve rapid
liquid absorption while avoiding problems like gel blocking. Cores
which contain multicomponent SAP fibers acquire liquids
sufficiently fast to avoid problems, like gel blocking, and,
therefore, the amount of fluff or pulp in the core can be reduced,
or eliminated. A reduction in the amount of the low-density fluff
results in a thinner core, and, accordingly, a thinner diaper.
[0241] Therefore, a diaper core can contain at least 50% of an SAP,
preferably at least 75% of an SAP, and up to 100% of an SAP. In
various embodiments, the presence of a fluff or pulp is no longer
necessary, or desired. In each case, the SAP in the core contains
multicomponent SAP fibers, in an amount of about 15% to 100% of the
SAP. The remaining SAP can be a second water-absorbing resin,
either basic or acidic. The second water-absorbing resin preferably
is not neutralized, but can have a degree of neutralization up to
100%. The multicomponent SAP fibers can be admixed with particles
of a second water-absorbing resin for introduction into a diaper
core. Alternatively, a diaper core can contain zones of
multicomponent SAP fibers and zones of a second water-absorbing
resin.
[0242] In addition to a thinner diaper, the present invention also
allows an acquisition layer to be omitted from the diaper. The
acquisition layer in a diaper typically is a nonwoven or fibrous
material, typically having a high degree of void space, or "loft,"
that assists in the initial absorption of a liquid. Cores
containing multicomponent SAP fibers can acquire liquid at a
sufficient rate such that diapers free of an acquisition layers are
practicable.
[0243] Many modifications and variations of the invention as
hereinbefore set forth can be made without departing from the
spirit and scope thereof and, therefore, only such limitations
should be imposed as are indicated by the appended claims.
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