Note: Descriptions are shown in the official language in which they were submitted.
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Absorption of Water
The present invention relates to the absorption of water cont~ining ions having a multipie
valency. More particularly, the present invention relates to the use of a water-absorbent
polymeric composition of the kind known as superabsorbent material to absorb water
cont~ining multiple valent ions, particularly divalent ions.
As used herein the term "water" when used alone or in phrases such as "water-absorbing",
"water-absorbent" and "water-swellable" is understood to mean not only water but also
aqueous media such as, in particular, electrolyte solutions such as body fluids.
A large number of compositions have been developed which exhibit the capacity to be water-
absorbing. Known compositions may be in any suitable form including powders, particles
and fibers Examples of two such water-absorbent compositions are described in US3,954,721 and 3,983,095, incorporated herein by reference, which disclose preparations for
derivatives of copolymers of maleic anhydride with at least one vinyl monomer in fibrous
form. The fibrous copolymers are rendered hydrophillic and water-swellable by reaction with
ammonia or an alkali metal hydroxide. US Patent No. 3 810 468, which is incorporated
herein by reference, discloses lightly cross-linked olefin-maleic anhydride copolymers
plG~dl~d as substantially linear copolymers and then reacted with a diol or a diamine to
introduce cross-linking. The result~nt lightly cross-linked copolymers are treated with
~mm~ni~ or an aqueous or alcohol solution of an alkali metal hydroxide. US Patent No. 3
980 663, which is incorporated herein by reference, describes water-swellable abso~
articles made from carboxylic polyelectrolytes via cross-linking with glycerine diglcidyl ether.
Eulu~eal~ Published Application No. 0 268 498 (incorporated herein by reference) describes
a water-absorbent composition formed by causing a substantially linear polymer of water-
soluble ethylenically ullsaluldted monomer blends comprising carboxylic and hydroxylic
monomers to cross-link int~n~lly.
Further examples of water-absolb~ compositions are those produced from copolymers of
an a, B unsaturated monomer having at least one pendant unit selected from a carboxylic acid
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group and deliv~liv~s thereof and a copolyll.elisable monomer.
A ~,lopollion of the pendant units are present in the final copolymer as the free acid and a
proportion as the salt of the acid. These copolymers are capable of being cross-linked, either
int~ lly or with a variety of cross-linking agents, to form the water-swellable composition.
l~xamples of water--swellable compositions of this type can be found in US 4,616,063,
4,705,773, 4,731,067, 4,743,244,4,788,237, 4,813,945, 4,880,868 and 4,892,533 and EP 0 272
074, 0 264 208 and 0 436 514. These patents and applications are incorporated herein by
reference.
Derivatives of carboxylic acid groups include carboxylic acid salt groups, carboxylic acid
amide groups, carboxylic acid imide groups, carboxylic acid anhydride groups, carboxylic acid
ester groups and the like.
Other examples of water-absorbent compositions can be found in US 4,798,861, W0
93/17066, W0 93~255735, W0 93/24684, W0 93/12275, EP 0 401 044, 0 269 393, 0 326 382,
0 227 305, 0 101 253, 0 213 799, 0 232 121, 0 342 919, 0 233 014, 0 268 498 and 0 397
410, GB 2082614, 2022505, 2270030, 2269602 and 21 '6591, US 4~18163, 3989586,
4332917, 4338417, 4420588 and 4155957 and FR 25251 ' 1 which are all incorporated herein
by reference.
Many of the known water-absorbent compositions having pendant carboxylic acid groups
have reduced ability to absorb water which coll~aills multi~ alent ions, such as divalent ions.
Without wishing to be bound by any theory, it is believed that the ions present in the water
react with the carboxylic acid groups. As the product of this reaction is insoluble, the
absorption of the ions results in the precipitation of the ~ ater-absorbent composition which
is then no longer capable of absorbing water.
This is a particular problem where the water to be absorbed contains a large proportion of
multivalent ions. One example of such water is sea water. which contains a number of salts
inrluAin~; divalent ionic salts such as MgC12, CaC12 and SrCl2. As a typical use of water-
absolL.~n~ compositions is as a wrap to protect under sea cables from the effects of sea water,
1 UTE SHEET (RULE 26)
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the ability to absorb sea water is particularly important. Multivalent ions can also be found
in other "waters" which are generally absorbed by these water-absorbent materials. Examples
of the waters include, general spillages, bodily fluids and the like.
We have now discovered that the aforementioned problems can be alleviated or overcame by
the use of a water-absorbent composition having pendant carboxylic acid groups arranged in
mutual proximity to absorb water co-,ti-;"i"g multivalent, particularly divalent ions. It will
be understood that the term "cont~ining" in-~lud~s the water absorption occurring in the
presence of the multivalent ions.
Thus, according to the present invention there is now pro- ided the use of a water--absorbent
composition to absorb water cont~ining multivalent ions wherein the water-absorbent
composition has pendant carboxylic acid groups and wherein two or more such groups react
with the ions and the composition does not precipitate.
The two or more such pendant carboxylic acid groups are preferably located in close
p~ iLy. Where the ion to be absorbed is divalent, the pendant carboxylic acid groups are
preferably located on the polymeric backbone in close proximity, most preferably, the
carboxylic acid groups are located on adJacent carbons on the backbone of the polymer.
Without wishing to be bound by any theory, it is belie~ ed that each of the carboxylic acid
groups in the two or more ~end~llL groups react with, and complex, the multivalent ion. Th
r~slllt~3nt composition does not ~ te thereby ~verco.ning the aforementioned problem.
DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS OF THE INVENTION
Particularly suitable copolymers for use in the production of the water--absorbing
compositions used in the present invention will contain from about ~S to about 75 mole
~ percent recurring units of at least one ~ -ulls~lu-dl~d monomer and from about 75 to about
25 mole percent recurring units of at least one copolymerizable monomer. The copolymer
preferably contains from about 35 to about 65 mole percent of recurring units of at least one
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K,~-unsaturated monomer and from about 65 to about 35 mole percent of at least one
copolymerizable co-monomer. Most preferably, the copolymer will be an equimolar
copolymer.
Suitable c~ n~t--r~tcd monomers are those bearing at least one pendant carboxylic acid
unit or derivative of a carboxylic acid unit. Derivatives of carboxylic acid units include
carboxylic acid salt groups, carboxylic acid amide groups, carboxylic acid imide groups,
carboxylic acid anhydride groups and carboxylic acid ester groups.
Examples of suitable a~ n!c;~t~ ted monomers include m~leic acid, crotonic acid, fumaric
acid, mesaconic acid, the sodium salt of maleic acid, the sodium salt of 2-methyl, 2-butene
dicarboxylic acid, the sodium salt of itatonic acid, maleamic acid, maleamide, N-phenyl
maleimide, maleimide, maleic anhydride, fumaric anhydride; itaconic anhydride, citraconic
anhydride; mesaconic anhydride, methyl itaconic anhydride, ethyl maleic anhydride,
diethylmaleate, methylmaleate; and the like, and their mixtures. Monomers having two
carboxylic acid groups ~tt~rh~orl to ad~acent carbon atoms are particularly preferred.
Any suitable copolymerizable co-monomer can be employed. Examples of suitable
copolymerizable co-monomers include ethylene, propylene, isobutylene, C, to C4 alkyl
methacrylates, vinyl acetate, methyl vinyl ether, isobutyl vinyl ether, and styrenic compounds
having the formula:
R-C-CH2
wherein R lCpl~,Se~ i hydrogen or an aL~cyl group having from 1 to 6 carbon atoms, and
wherein the benzene ring may be sub:~ilul~d with low molecular weight alkyl or hydroxyl
groups.
Suitable Cl to C4 alkyl acrylates include, for example, methyl acrylate, ethyl acrylate,
isoplupyl acrylate, n-propyl acrylate, n-butyl acrylate, and the like, and their mixtures.
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Suitable C, to C4 alkyl methacrylates include, for example, methyl methacrylate, ethyl
methacrylate, isopropyl methacrylate, n-propylmethacrylate, n--butyl methacrylate, and the
like, and their mixtures.
Suitable styrenic compounds include, for example, styrene, a-methylstyrene, p-methylstyrene,
t-b~lLy~y~ e, and the like, and their mixtures.
The pendant units on the a,~3-unsaturated monomer, will determine what, if any, additional
reactions must be carried out to obtain a copolymer having the requisite pendant units
necessary to produce the water-absorbing compositions of this invention. Preferably these
water-absorbing compositions will contain from about '0 to about 80 percent pendant
carboxylic acid units and from about 80 to about 20 percent pendant carboxylate salt units.
Prefe}ably, both units are present in an amount of from about 30 to about 70 percent.
In general, if the cc,B--Inc~t-lr~tçcl monomer bears only carboxylic acid amide, carboxylic acid
imide, carboxylic acid anhydride, carboxylic acid ester groups or mixtures thereof, it will be
n~.cçc.c~ry to convert at least a portion of such carboxylic acid derivative groups to carboxylic
acid groups by, for example, a hydrolysis reaction. If the c~,B-unsaturated monomer bears
only carboxylic acid salt groups, acidification to form carboxylic acid groups will be
neceSs;~,~/ using methods and materials well known in the art
Similarly, the final copolymer should contain from about 80 to 20 percent pendant carboxylate
salt units. Accordingly, it may be necessary to carry out a neutralization reaction.
Neutralization of carboxylic acid groups with a strong organic or inorganic base such as
NaOH, KOH, ammonia, ammonia-in-water solution, or organic amines will result in the
formation of carboxylate salt units, preferably carboxylate metal salt units.
The sequence and the number of reactions (hydrolysis, acidification, neutralization, etc)
carried out to obtain the desired functionality attached to the copolymer backbone are not
critical.
One copolymer particularly suitable for use in the present invention is a copolymer of maleic
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anhydride and isobutylene. Another is maleic anhydride and styrene. Suitable copolymers
will have peak average molecular weights of from about 6,000 to about 500,000 or more.
~iuitable copolymers of maleic anhydride and isobutylene can be ~cpdl~d using any suitable
COIlv~ llLional method. Such copolymers are also commercially available from Kurary Isoprene
Chemical Company, Ltd., Tokyo, Japan under the tr~ nnz~rk ISOBAM. ISOBAM copolymers
are available in several grades which are lliL[tl~ ted by average viscosity molecular weight:
ISOBAM--10, 160,000 to 170,000; ISOBAM-06, 80,000 to 90,000; ISOBAM-04, 55,000 to
65,000 and ISOBAM-600, 6,000 to 10,000.
The copolymer is then preferably cross-linked either intemally via covalent or hydrogen
bonding or using an external cross-linking agent. Suitable cross-linking agents include:
monomers co.-t~;"i"g at least two hydroxyl groups such as alkylene glycols cont~ining Z-10
carbon atoms and their ethers, cycloalkylene glycols, Bisphenol A, hydroxy alkylene
derivatives of Bisphenol A, hydroquinone, phloroglucinol, hydroxy alkylene derivatives of
diphenols, glycerols, Glylhlilol, pentaclylhlilol, and mono--, di- or oligt~s~r~h~rides;
heterQcyclic carbonates; and monomers CO~ ;llil.p at least one amine group and at least one
hydroxyl group such as ethanolamine, tris (hydroxymethyl) aminomethane, 3-amino-1-
propanol, DL--1-amino--2-propanol, 2-amino-1-butanol, N,N-dimethylethanolamine,
diiso~lopa,lol-amine methyl diethanol amine, triethanol amine, 2-(methylamino)ethanol and
the lil~e.
In general cross--linking will not occur and the product will not become absorbent until the
partially neutralized polymer reaction product is heated to a telllpl laLLIlG sufficient to effect
reaction between the cross-linking agent and the copolymer.
The cure conditions required to achieve optimal cross-linking depends upon several factors,
including the particular polymer employed. For example, the cure tt~ .atulG will depend
on the polymer. If the polymer is a partially neutralized ethylene/maleic anhydride
copolymer, a cure teul~ldlule of at least 140~C will be required to achieve cross-linking.
If the polymer is partially neutralized styrene/maleic anhydride copolymcr, a telll~ dlulG of
at least about 150~C is required to cross-link; and if a partially neutralized isobutylene/maleic
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anhydride copolymer is employed, a tell.pc.dLure of at least about 170~C will be required to
achieve cross-linking Cure times can vary dep~ntling on cure te.~,eldtures and on the
amount of reactive compound used. Cure times will typically be within the range of from
about 0.5 to about 20 minlltes, preferably 0.5 to 15 minutes, and most preferably 0.5 to 12
minutes. To m~imi~e absoll,tlll pl~yellies, optimal cure of the composition (ie. minim~l
amount of cross-linking needed to form a cross-linked network) is required. Optimal cure
is achieved by adjusting a number of variables within wide ranges depending upon the
specific syrup composition. Optimal cure conditions require, among other things, a balance
between cure time and cure te~ eldlulc.
As is readily a~pdlcllt from the high te~ eldtulc required to achieve cross-linking, the
aqueous reaction product of the partially neutralized polymer and the reactive compound, ie.
the grafted polymer syrup, can be stored for an unlimited time. This unlimited room
lclllp~ldture stability facilitates further processing of the syrup into any number of
conventional forms, in~ lu-ling fibers and films using conventional methods. For example, the
syrup can be further processed by casting, spray drying, air-assisted spray drying, air
~ttrml~tion, wet spinning, dry spinning, flash spinning, and the like. To facilitate the removal
of water from the aqueous composition during the spinning process, minor amounts of other
polar solvents such as alcohol can be added to the aqueous syrups. The rçsnlt~nt fibers can
be further processed into milled fibers, chopped fibers, fluff or bulk fibers, strands, yarns,
webs, composites, woven fabrics, non-woven fabrics, non-woven mats, tapes, scrim, and the
like, using a variety of methods including twisting, beaming, sl~hing, warping, quilling,
severing, crimping, lrxL~ g~ weaving, knitting, braiding, etc., and the like.
The water-absorbent compositions may be formed into a composite web colllL lisi~g non-
water absorbent fibers and water-absorbent fibers. The fibers of these webs may be bonded
using any suitable technique. Suitable non-water-absorbent fibers include rayon fiber,
cellulose ester fiber, protein fiber, polyamide fiber, polyester fiber, polyvinyl fiber, polyolefin
fiber, polyurethane fiber, aramid fiber, glass fibers and mixtures thereof.
The composite webs may be used in articles of m~nllf~cture such as disposable diapers,
sdllildly napkins, tampons, pant liners, adult incontinence pads, coverstock for r~ h~e
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hygiene products, surgical and dental sponges, bandages, patient underpads (for example pairs
of the type described in US5814101, US4342314 and EP0052403 when are incorporated
herein by reference), wipes, domestic wipes, industrial wipes, pacl~ging, filters, medical tray
pads, fenestration drapes, opelalillg gowns; mortuary pads, other medical related devices,
casket liners, forensic rx,~ tion pads, cable wrap, food tray pads, food preservation articles,
seed germination pads, capillary mats, baby bibs, desiccant strips for anti-rust use, bath mats,
sorbents, breast pads, underarm pads, wound covers, pet litter, roofing materials, automotive
trim, furniture, bedding, clothing, soil modifiers, spill control materials; waste m~n~gement
materials and protective articles.
These articles of m~nllf~/ hlre are found to be particularly effective in absorbing water
co"l~i"i"g multivalent ions, particularly divalent ions.
Water cont~ining divalent ions include sea water, menses and urine The composition of
synthetic sea water - which is believed to correspond to a typical sea water - is set out in
Table 1.
Table 1
Salt g/l
NaCl 24.54
MgC12 ~ 6H2~ 11.10
Na2S04 4.09
CaCl2 1.16
KCl 0.69
NaHCO3 0.20
KBr 0.10
H3B03 0.03
SrC12 ~ 6H2~
NaF 0.003
It can therefore be seen that sea water Collt~il.s a substantial amount of divalent ions.
Therefore using the compositions of the present invention as cable wrap for undersea
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applications is particularly suitable to protect the cable from the effect of the sea water.
The composition of synthetic adult urine - which is believed to correspond to typical adult
urine - is set out in Table 2.
Table 2
Ingredients g/L
Urea 20.5
NaCI 8.5
(NH3)2 2.5
K2S04 4.0
Citric acid H2
MgC12- 6H20 1.1
CaCI2 ~ 6H20 0.8
L. Histidine HCl 0.7
Albumine bovine 0.1
Preserving agent 1.0
Deionised water 960.3
pH Adjuster 6.0
It can therefore be seen that adult urine contains a substantial amount of divalent ions.
Therefore, the compositions of the present invention are particularly useful in, for example,
adult incontinence pads.
The following examples are illustrative of the present invention but should not be construed
as limitin~; the invention in any way.
Prepared samples of water-absorbent compositions were tested for water absorbency and fluid
retention using the "tea bag" test.
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The "tea bag" test was carried out as follows. First 10 pieces of tea bag paper are cut to 5"
x 2" and folded to 2.5" x 2" and heat sealed on 2 sides. These bags are then soaked in a test
solution, removed, dabbed lightly with filter paper to remove excess saline solution and
weighed. These weights are then averaged and the value is recorded as "W2". In to a
triplicate set of tea bags measuring 5" x 2" is placed a~pio~c;lll~tely 0.2 grams of water-
absorbent solvent, the exact weight of which is recorded as "W3", the bags loaded with the
sample are heat sealed. The triplicate sample CO~ .i"i"g tea bags are then placed in a test
solution, with stirring~ for 10 minllt~ c. Each tea bag is then removed from the test solution,
allowed to drain for 10 seconds and then dabbed lightly with filter paper to remove excess
test solution. Each sample co,.l;.;~i"g tea bag is then weighed and recorded as "Wl". Each
sample cont~ining tea bag is then placed in a Buchner porcelain funnel, a small amount of
test solution is poured over the same to re-saturate it, and then the sample cont~ining tea bag
Is exposed to a vacuum of 0.5 psi for 5 minl-tes The sample is removed and weighed and
the weight is recorded as "W4".
The Free Swell Liquid Retention (FS) is det~nnin~d using the formula:
g/g=[Wl-W~/W3]--1
The 0.5 psi Liquid Retention (Rl~ is ~ tçnnin~fl using the fo~nula:
g/g=[W4--W2)/W3] -- 1
where W, = final free swell weight in grams of gel plus wet tea bag,
W2 = average weight in grams of 10 empty, wet tea bags,
W3 = original weight in grams dry staple fiber, and
W4 = final 0.5 psi weight in grams of gel plus wet tea bag.
Examples
Commercially available water-abso~ nt powders A and B were tested in accordance with
the above-mentioned test protocols. A water--absorbent composition of the preferred
embodiments of the invention were pl~pal~d and tested according to the above-mentioned
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test protocols. Th~ results Or the tests are set out ln Table 3.
Table 3
Test Solution Comoosition of Powder A Powder B
the mYention
F.S. R.T. F.S. ' R.T. F.S. R.T.
n-i~ni~d wa~er 351.7 249.8 278.1 190 6 209.2 148.1
0.170 CaCI. 117 92.4 58.5 50 1 73.6 59.3
0.3% CaClz 62.1 38.6 19.3 1 10 26.1 16.1
0.5% C~Cl2 ~6.5 36.1 g.6 1 7 1 5.5 3.5
l~a CaCIz ~3.2 27.9 3.49 2 17 lQ.~ 5.8
0.5~ C2~O~)~ 70.3 52.9 18.3 1~ 5 33 4 26.7
l~ C~O~)~ 47 34.1 6.2 ' 5.5 7 6
0.5% FeS0, 81 56.9 33 25 ~ 22.4 15.8
1% FeS0~ 64.2 35 7 13.5 7 7 8 6 3.2
0.1 % F~(SO~)~ I 12.7 80.2 95 74.3 1oa.2 75.5
0.5% F~(SO4), 43.4 24.7 4~.1 ;0 8 38.9 29.6
O.l~o MgSO, 122.5 87.7 85.5 61.4 69 5 50.8
0.5~o MgSO~ 66 43.4 20 12 2 23.2 15.8
l~ MgSO~ 55 42.7 11.9 9.3 7.5 6
s~wu~r 51.4 38.4 11.3 10.2 11.~ 8.7
(synth~tEc)
S~a Water 57.5 43.8 lg.5 16.2 14.9 l 2 2
~v~
l~ Urca 372.8 239 268.1 171 3 2~2.5 151.3
s~ ur a 351.9 233.2 260.4 171.7 238.6 148.4
10% Ur:a 247 177.2 230.9 172.1 215.8 151.7
0.5% ZnSO4 78.5 54.2 42.1 30.3 45.5 3l~6
1~ ZnSO4 67.7 50.9 20.8 15.1 20 5 13.5
2% ZnSO~ 53.5 39.8 14.2 10.3 10 2 6
SUBSTITUTE SHEET (RULE 26)
