Note: Descriptions are shown in the official language in which they were submitted.
21 95373
HOECHST AKTIENGESELLSCHAFT HOE 96/F 040 Dr. My
Description
5 Process for preparing hydrophilic highly swellable hydrogels
The present invention relates to a process for preparing hydrophilic highly swellable
hydrogels by mixing fine grain into hydrophilic highly swellable hydrogel in aqueous
gel form.
Hydrophilic highly swellable hydrogels are, in particular, polymers comprising
(co)polymerized hydrophilic monomers, graft (co)polymers of one or more
hydrophilic monomers on an appropriate graft base, crosslinked cellulose ethers or
starch ethers, or natural products, for example guar derivatives, which can be
15 swollen in aqueous liquids.
Synthetic products of this kind can be prepared by known polymerization techniques
from appropriate hydrophilic monomers, for example acrylic acid. Polymerization in
aqueous solution by the technique known as gel polymerization is preferred. Thisgives rise to polymers in the form of aqueous jellies which, following mechanical
20 comminution using appropriate apparatus, can be obtained in solid form by means
of known drying processes.
The grinding of these superabsorbent polymers obtained in solid form is
automatically accompanied by the formation of fine particles which, owing to their
low size, are unsuitable for use in diapers, incontinence articles and sanitary towels
25 since they lead to metering difficulties and dusting, and have a reduced swelling
capacity. Fine components in water-swellable polymer articles lead to products of
reduced swelling capacity as a result of the phenomenon known as gel blocking.
Gel blocking describes the apparent reduction in the absorbency for aqueous
liquids, caused by the formation of a flowing gel which surrounds or encloses as yet
30 unswollen superabsorbent polymer particles, so that liquid transport to the surface
of these as yet unswollen particles is prevented. For these reasons, polymeric fine
components smaller than 0.100 mm, preferably smaller than 0.150 mm, are
separated off before being used in sanitary articles, by sieving for example.
Depending on the sieve cut off, up to 25% water-swellable fine components are
-
- 21 95373
produced which to date it has only been possible to employ to a highly restricted
extent for speciality applications.
Since the water-swellable polymeric fine components constitute a considerable
economic factor, there has been no lack of attempts to convert them to a reusable
form.
For instance, DE-A 37 41 157 describes agglomeration through the composition of
granules, by subjecting a mixture of water-swellable, polymeric fine particles and
meltable or sinterable pulverulent solids to heat treatment.
In DE-A 37 41 158, a process is described for agglomerating water-swellable
polymeric fine components, wherein solutions or dispersions are used to compose
agglomerates. However, the disadvantage of agglomerated fine components is theirlow stability with respect to mechanical loads as occur, for example, in the course of
transportation and processing.
W O 92/01008 describes a process for preparing water-swellable products using
ultrafine components of water-swellable polymers, which comprises dispersing thewater-swellable polymeric ultrafine components in a monomer which is liquid at
room temperature, mixing this dispersion with an aqueous monomer solution,
polymerizing the mixture, comminuting the polymer and drying the comminuted
solid.
EP-A 513 780 describes a process for recycling dry polymer fine grain which
absorbs aqueous solutions, wherein the fine grain is mixed with a monomer solution
which is then polymerized.
However, the addition of fine grain to the monomer solution raises the solids
concentration of the monomer solution, and the proportion of transfer reactions of
the growing free-radical polymer chains onto already formed or existing polymer
increases. As a result, more highly crosslinked products are obtained, which have a
correspondingly low absorbency for aqueous liquids.
EP-A 463 388 describes the conversion of the superabsorbent fine grain into larger
particles, the superabsorbent particles of fine grain being mixed with the addition of
water into the gel which is obtainable from the polymerization of the aqueous
monomer solution and this mixture being subsequently dried. The mixing-in
operation described in this document, of superabsorbent fine-grain particles into the
gel obtainable from the polymerization of the aqueous monomer solution, is
2 1 95373
technically complex, since the homogeneous distribution of the fine grain is
hindered by the above-described blocking phenomenon, and unwetted, dry fine-
grain particles can be enclosed by the polymer gel. In addition, for mixing the fine
grain into the polymer gel this process requires large amounts of water, in fact from
5 4 to 7 parts of water per part of fine grain to be mixed in, and this water must be
removed again by drying.
The object of the present invention, therefore, is to convert superabsorbent fine-
grain particles into a (re)useable form without the disadvantages associated with the
10 prior-art processes.
The present invention therefore provides a process for preparing hydrophilic highly
swellable hydrogels by mixing fine particles of a hydrophilic highly swellable
hydrogel into a hydrophilic highly swellable hydrogel in aqueous gel form with the
15 addition of water, wherein the mixing-in operation is carried out in the presence of a
surfactant.
By fine particles of a hydrophilic highly swellable hydrogel there are meant,
,ureferably, particles with a size of less than 0.1 mm, particularly preferably less
20 than 0.15 mm. Such particles are obtained in particular, as described above, in the
course of sieving dried and ground hydrophilic highly swellable polymers.
The term hydrophilic highly swellable hydrogel in aqueous gel form refers preferably
to a product obtained directly by gel polymerization of suitable hydrophilic
monomers that is customarily dried, ground and sieved for further use.
25 It is also possible to convert hydrogels obtained in other ways, for example by
addition of water, into a corresponding aqueous gel form.
Said hydrogel in aqueous gel form preferably has a solids content of from 15 to 50%
by weight, particularly preferably from 15 to 30% by weight. However, solids
30 contents of more than 50% by weight are equally possible.
The fine-grain particles to be employed in accordance with the invention preferably
constitute a product which has been obtained in the course of the above-described
sieving of a polymer obtained by gel polymerization of suitable hydrophilic
21 95373
monomers, and subsequent drying and grinding. Consequently, fine-grain particlesto be employed in accordance with the invention and hydrogel in aqueous gel formpreferably have the same chemical composition.
5 In accordance with the present invention, preferably from 2 to 10 parts, particularly
preferably from 5 to 8 parts, of fine-grain particles, preferably from 0.2 to 10 parts,
particularly preferably from 1 to 4 parts, of water, and preferably from 0.01 to 0.2
part, particularly preferably from 0.015 to 0.15 part, of surfactant are mixed into 100
parts of the hydrophilic, highly swellable hydrogel in aqueous gel form that is
10 obtained by gel polymerization.
The mixing of the fine-grain particles, the water and the surfactant into the
hydrophilic highly swellable hydrogel in aqueous gel form can be undertaken in
various ways. Preference is given to mechanical comminution of the aqueous gel in
a meat grinder, addition thereto of fine-grain particles, water and surfactant, and
15 homogeneous mixing in by means of renewed mincing in a meat grinder. In this
context, fine-grain particles, water and surfactant can be added in various
sequences. It is thus possible first of all to distribute the fine-grain particles in the
aqueous gel and then to add the surfactant together with the water in the form of a
solution or dispersion. However, the fine-grain particles and the mixture of
20 surfactant and water can also be added simultaneously. Another option is first to
make a paste of the fine-grain particles with the mixture of surfactant and water, and
to add this paste to the aqueous gel. In a particularly preferred procedure, the fine-
grain particles are made into a paste with a portion of the mixture of surfactant and
water, and added to the aqueous gel. The homogeneous mixing-in of these pasted
25 fine-grain particles is facilitated by the simultaneous or subsequent addition of the
remaining portion of the mixture of surfactant and water to the aqueous gel.
Praferably, from 40 to 60% of the mixture of surfactant and water is used to make up
a paste from the fine-grain particles, and from 60 to 40% of the mixture of surfactant
and water is added directly to the aqueous gel.
30 Following the admixture of fine-grain particles in the presence of water and
surfactant, the product can be dried, ground and, if desired, sieved, all in
conventional manner.
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In accordance with the invention it is possible to use all nonionic, anionic, cationic or
amphoteric surfactants, preference being given to those which are soluble or at
least dispersible in water. The HLB value of the surfactants is therefore preferably
greater than or equal to three (For definition of HLB value see W.C. Griffin, J. Soc.
Cosmetic Chem. 5 (1954) 249).
Examples of suitable nonionic surfactants are the adducts of ethylene oxide,
propylene oxide or mixtures of ethylene oxide and propylene oxide with alkyl
phenols, aliphatic alcohols, carboxylic acids or amines. Suitable examples are
(C8-C24)-alkylphenols alkoxylated with ethylene oxide and/or propylene oxide.
Examples of commercial products of this kind are octylphenols and nonylphenols
each reacted with from 4 to 20 mol of ethylene oxide per mol of phenol. Other
suitable nonionic surfactants are ethoxylated (C10-C24) fatty alcohols, ethoxylated
(C10-C24) fatty acids, and ethoxylated (C10-C24) fatty amines and ethoxylated (C10-
C24) fatty acid amides. Also suitable are polyhydric (C3-C6) alcohols esterified with
(C~o-C24) fatty acids. These esters may have been additionally reacted with from 2
to 20 mol of ethylene oxide. Examples of suitable fatty alcohols which are
alkoxylated to prepare the surfactants are palmityl alcohol, stearyl alcohol, myristyl
alcohol, lauryl alcohol, oxo alcohols, and unsaturated alcohols, such as oleyl
alcohol. These fatty alcohols are ethoxylated or propoxylated, or reacted with
ethylene oxide and propylene oxide, to a degree such that the reaction products are
soluble in water. In general, 1 mol of the above fatty alcohols is reacted with from 2
to 20 mol of ethylene oxide and, if used, up to 5 mol of propylene oxide so as to give
surfactants having a HLB value of more than 8.
Examples of (C3-C6) alcohols which are partially esterified and, if desired,
ethoxylated are glycerol, sorbitol, mannitol and pentaerythritol. These polyhydric
alcohols are partially esterified with (C10-C24) fatty acids, for example oleic acid,
stearic acid or palmitic acid. Such esterification with the fatty acids takes place at
the most up to a degree such that at least one OH group of the polyhydric alcohol
still remains unesterified. Examples of suitable esterification products are sorbitan
monooleate, sorbitan tristearate, mannitol monooleate, glycerol monooleate and
glycerol dioleate. Said fatty acid esters of polyhydric alcohols which still contain at
least one free OH group can be modified further by reaction with ethylene oxide,
21 95373
propylene oxide or mixtures of ethylene oxide and propylene oxide. Preference isgiven to the use of from 2 to 20 mol of said alkylene oxides per mole of fatty acid
ester. As is known, the degree of ethoxylation influences the HLB value of the
nonionic surfactants. By an appropriate choice of alkoxylating agent, and amount of
5 alkoxylating agent, it is possible in a technically simple manner to prepare
surfactants having HLB values in the range from 3 to 20.
A further group of suitable surfactants comprises homopolymers of ethylene oxide,
block copolymers of ethylene oxide and alkylene oxides, preferably propylene oxide,
and polyfunctional block copolymers which are formed, for example, by sequential10 addition of propylene oxide and ethylene oxide onto diamines.
Also suitable are alkylpolyglycosides as are marketed, for example, under the trade
names '19APG, ~GIucopan and ~'PIantaren.
The nonionic surfactants can be used either alone or else in a mixture with one
another.
Suitable anionic surfactants are (C8-C24)-alkylsulfonates, which are preferably in the
form of the alkali metal salts, (C8-C24)-alkyl sulfates, which are preferably employed
in the form of the alkali metal or trialkanolammonium salts, such as, for example,
triethanolammonium lauryl sulfate, sulfosuccinic diesters, for example the sodium
20 salt of di(2-ethylhexyl) sulfosuccinate, sulfosuccinic monoesters, for example sodium
lauryl sulfosuccinate or disodium fatty alcohol polyglycol ether sulfosuccinate,(C8-C24)-alkylarylsulfonic acids, and the sulfuric half-esters of adducts of ethylene
oxide with alkyl phenols or fatty alcohols.
25 Examples of suitable cationic surfactants are the salts of fatty amines, for example
coconut-fatty ammonium acetate, quaternary fatty acid amino esters, for example di-
fatty acid isopropyl ester dimethylammonium methosulfate, quaternary fatty acid
aminoamides, for example N-undecylenic acid propylamido-N-trimethylammonium
methosulfate, adducts of alkylene oxides with fatty amines or salts of fatty amines,
30 for example pentaoxethylstearylammonium acetate or ethoxylated methyl-oleamine
methosulfate, and also long-chain alkylbenzyldimethylammonium compounds, such
as (C10-C22)-alkyl-benzyldimethylammoniumchloride.
21 95373
Examples of suitable amphoteric surfactants are, in particular, compounds which in
the same molecule carry at least one quaternary ammonium cation and at le~ast one
carboxylate or sulfate anion, such as, for example, dimethylcarboxymethyl-fatty acid
alkylamidoammonium betaines, or 3-(3-fatty acid-amido-propyl)dimethylammonium
5 2-hydroxypropanesulfonates.
The ionic surfactants can be used alone or else in a mixture with one another.
Suitable hydrophilic highly swellable hydrogels which can be prepared in
10 accordance with the invention are, in particular, polymers comprising
(co)polymerized hydrophilic monomers, graft (co)polymers of one or more
hydrophilic monomers on an appropriate graft base, crosslinked cellulose ethers or
starch ethers, or natural products, for example guar derivatives, which can be
swollen in aqueous liquids. These hydrogels are known to the skilled worker.
15 Examples of hydrophilic monomers suitable for preparing these hydrophilic highly
swellable polymers are polymerizable acids, such as acrylic acid, methacrylic acid,
vinylsulfonic acid, vinylphosphonic acid, maleic acid including its anhydride, fumaric
acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-
methylpropanephosphonic acid, and the amides thereof, hydroxyalkyl esters, and
20 amino- or ammonium group-containing esters and amides, and also water-soluble N-vinylamides or else diallyldimethylammonium chloride.
Preferred hydrophilic monomers are compounds of the formula I
R\C C R 1 (I)
H \R 2
in which
30 R1 is hydrogen, methyl or ethyl,
R2 is the group -CooR4, sulfonyl, phosphonyl, phosphonyl esterified with (C1-C4)-
alkanol, or a group of the formula
21 95373
o ~
I
j C~ / C~ ~ R
CH3
R3 is hydrogen, methyl, ethyl or carboxyl,
R4 is hydrogen, amino or hydroxy-(C1-C4)-alkyl, and
R5 is sulfonyl, phosphonyl or carboxyl.
Examples of (C1-C4)-alkanols are methanol, ethanol, n-propanol and n-butanol.
Particularly preferred hydrophilic monomers are acrylic acid and methacrylic acid.
Hydrophilic hydrogels which can be obtained by polymerizing olefinically
unsaturated compounds are already known and are described, for example, in US
4,057,521, US 4,062,817, US 4,525,527, US 4,286,082, US 4,340,706 and US
4,295,987.
Hydrophilic hydrogels which are obtainable by graft copolymerization of olefinically
unsaturated acids on various matrices, such as polysaccharides, polyalkylene
oxides and derivatives thereof, for example, are also already known and are
described, for example, in US 5,011,892, US 4,076,663 or US 4,931,497.
Appropriate graft bases can be natural or synthetic in origin. Examples are starch,
cellulose or cellulose derivatives and other polysaccharides and oligosaccharides,
polyalkylene oxides, especially polyethylene oxides and polypropylene oxides, and
hydrophilic polyesters.
Suitable polyalkylene oxides, for example, have the formula
X
R6-o-(CH2-CH-o)n-R7
21 95373
in which
R6 and R7 independently of one another are hydrogen, alkyl, alkenyl or aryl,
X is hydrogen or methyl and
n is an integer from 1 to 10,000.
R6 and R7 are preferably hydrogen, (C1-C4)-alkyl, (C2-C6)-alkenyl or phenyl.
Particularly preferred hydrogels are polyacrylates, polymethacrylates and the graft
copolymers described in US 4,931,497, US 5,011,892 and US 5,041,496. The
content of these patent documen~s is expressly included as part of the present
disclosure.
The hydrophilic highly swellable hydrogels are preferably crosslinked; in other
words, they include compounds having at least two double bonds which are
copolymerized into the polymer network.
Particularly suitable crosslinkers are methylenebisacrylamide and
methylenebismethacrylamide, esters of unsaturated mono- or polycarboxylic acids
with polyols, such as diacrylate or triacrylate, for example butanediol or ethylene
glycol diacrylate or dimethacrylate, and also trimethylolpropane triacrylate, and allyl
compounds, such as allyl (meth)acrylate, triallylcyanurate, diallyl maleate, polyallyl
esters, tetraallyloxyethane, triallylamine, tetraallylethylenediamine, allyl esters of
phosphoric acid, and also vinylphosphonic acid derivatives as are described, forexample, in EP-A 343 427. The content of EP-A 343 427 is expressly also part of
the present disclosure.
Over and above this, the hydrophilic highly swellable hydrogels are, with particular
preference, aftercrosslinked in aqueous gel phase in a manner known per se.
The hydrophilic highly swellable hydrogels can be prepared by polymerization
techniques which are known per se. Preference is given to polymerization in
aqueous solution by the technique known as gel polymerization. In this
polymerization, from 15 to 50% by weight aqueous solutions of one or more
hydrophilic monomers and, if desired, an appropriate graft base are polymerized in
the presence of a free-radical initiator, preferably without mechanical mixing,
utilizing the Trommsdorff-Norrish effect (Bios Final Rep. 363.22; Makromol. Chem.
21 qS373
1, 169 (1947)).
The polymerization reaction can be carried out in the temperature range between
0C and 150C, preferably between 10C and 100C and under atmospheric
pressure or else under elevated or reduced pressure. As is conventional,
5 polymerization can also be performed in an inert-gas atmosphere, preferably (~nder
nitrogen.
For initiating the polymerization it is possible to employ high-energy electromagnetic
radiation or the customary chemical polymerization initiators, for example organic
peroxides, such as benzoyl peroxide, tert- butyl hydroperoxide, methyl ethyl ketone
10 peroxide, cumene hydroperoxide, azo compounds, such as azodiisobutyronitrile,and inorganic peroxy compounds, such as (NH4)2S2O8 or K2S2O8 or H2O2, alone or
in combination with reducing agents such as sodium hydrogen sulfite, and iron(ll)
sulfate or redox systems whose reducing component comprises an aliphatic or
aromatic sulfinic acid, such as benzenesulfinic acid and toluenesulfinic acid, or
15 derivatives of these acids, such as, for example, Mannich adducts of sulfinic acid,
aldehydes and amino compounds, as are described in DE-C 1 301 566.
By subsequently heating the polymer gels for a number of hours in the temperature
range from 50 to 1 30C, preferably from 70 to 1 00C, it is possible further toimprove the quality properties of the polymers.
The novel addition of surfactant effectively reduces the tendency of the fine-grain
particles toward gel blocking and, consequently, makes it possible to mix them more
readily, and homogeneously, into the hydrophilic highly swellable hydrogel in
aqueous gel form, using significantly lower amounts of water than in the prior art.
25 If the fine-grain particles are not mixed homogeneously into the aqueous gel, then
the addition of water is accompanied by the formation of hard, solid agglomerates of
fine-grain particles, which may lead to mechanical problems in the apparatus
components and which, owing to their size cannot be removed by sieving, yet
nevertheless display the phenomenon of gel blocking in terms of the absorption of
30 aqueous liquids. It is therefore necessary to minimize the proportion of such hard,
solid agglomerates of fine grain particles in the end product in order to obtain the
desired rapid uptake of aqueous liquids. The rate of liquid uptake by
superabsorbent polymer particles can be determined by the vortex test:
21 95373
For this test, 50 ml of a 0.9% by weight aqueous NaCI solution are placed in a
100 ml glass beaker, and this solution is stirred at 600 rpm with the aid of a
magnetic stirrer and a stirrer bar. 2 9 of the superabsorbent polymer under test are
added rapidly at the edge of the stirring vortex formed in this system, and a
5 measurement is made of the time required to bring the vortex to a standstill as a
result of complete gelling. This time is shorter the lower the proportion, in the total
test sample, of particles which exhibit the phenomenon of gel blocking.
The hydrophilic highly swellable hydrogels prepared in accordance with the
10 invention are outstandingly suitable as absorbents for water and aqueous liquids,
such as urine or blood, in sanitary articles such as baby and adult diapers, sanitary
towels, tampons and the like. However, they can also be used as soil conditioners in
agriculture and horticulture, as moisture binders in the sheathing of cables, and for
thickening aqueous wastes.
The invention is illustrated by the following examples:
Comparison Example I
10 parts of superabsorbent fine-grain particles are combined with 2 parts of water,
the fine-grain particles agglomerating to form a single clump of rubberlike
consistency. It is impossible to mix this agglomerate homogeneously into polymergel, however great the amounts of water added.
Example I
10 parts of superabsorbent fine-grain particles are combined with 2 parts of water to
which the parts of surfactant indicated in Table I have been added. In this case, a
30 wetted but still free-flowing powder is obtained each time. This powder can be mixed
and distributed without problems into 200 parts of polymer gel with a solids content
of 25% by weight, this process being assisted by a subsequent addition of 2 parts of
water to this mixture.
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12
Table I
Test Surfactant added to the waterParts of surfactant
1 -1 Genagen~' CA-050 0.12
1 - 2 Tween~ 80 0.08
1 - 3 SPAN~ 20 0.06
1 - 4 Plantaren ~2 000 UPNP 0.05
1 - 5 Hostapur~SAS 30 0.03
1 - 6 C12-/C14-Alkylbenzyldimethylammonium 0.18
chloride
1-7 Ampholyt~JB 130/K 0.25
1 - 8 DSIE adduct 0.30
Genagen~ CA-050 (Commercial product from Hoechst AG) is a coconut-fatty acid
monoethanolamide polyglycol ether
15 Tween~D 80 (Commercial product from ICI) is polyethylene oxide-(20)-sorbitan
monooleate
SPAN 20 (Commercial product from ICI) is sorbitan monolaurate
Plantaren~ 2 000 UPNP (Commercial product from Henkel KgaA) is an
alkylpolyglycoside
20 Hostapur SAS 30 (Commercial product from Hoechst AG) is a mixture of n-
alkanesulfonates which is prepared by sulfoxidation of n-paraffins
DSIE adduct is the reaction product of distearylimidazoline ester with lactic acid
Ampholyt~D JB 130/K (Commercial product from Huls AG) is a cocoamidopropyl
betaine
Comparison Example ll
800 parts of acrylic acid are diluted with 800 parts of water, and this solution is
reacted with 644.38 parts of a 25% by weight sodium hydroxide solution, with
30 cooling by ice. This reaction mixture is placed together with 2 parts of
methylenebisacrylamide and 1916.22 parts of water in an unheated and insulated
21 95373
reactor. Nitrogen is blown through the solution, and the temperature of the solution
is reduced to 10C. When the o3(ygen dissolved in the solution was below 1 ppm,
the following initiators were added in the sequence given:
0 8 part of 2,2-azobisamidinopropane dihydrochloride in 10 parts of water
0.008 part of ascorbic acid
0.23 part of a 35% by weight aqueous hydrogen peroxide solution.
After an induction phase of 20 minutes, polymerization began, and a maximum
temperature of 60C was reached within 2 hours. The gel thus obtained was left in
the insulated reactor for 2 hours more, thereby reducing the residual monomer
content of acrylic acid in the gel to below 1,000 ppm.
After the polymer gel had been comminuted in a meat grinder, 644.38 parts of a
25% by weight sodium hydroxide solution were added to the gel. Prior to the
addition of the sodium hydroxide solution, the temperature of the gel was
approximately 60C and the temperature of the sodium hydroxide solution was
38C. The gel was passed again through the meat grinder in order to achieve goodmixing of the gel with the sodium hydroxide solution and thus homogeneous
neutralization of the gel. This gel, which as a result of the exothermic neutralization
reaction now had a temperature of 75-80C, was admixed simultaneously with 230
parts of superabsorbent fine-grain particles and 1000 parts of water. The gel was
subsequently passed three times more through the meat grinder in order to
distribute the fine-grain particles in the gel with maximum homogeneity.
Nevertheless, relatively small, highly solid agglomerates of fine-grain particles can
still be made out in the gel. The gel mechanically comminuted in this way was dried
with hot air at 150C. The polymer is subsequently ground and sieved to a particle
range of 0.150-0.800 mm.
The water-absorbing polymer has the following properties:
Retention: 45 9l9
Vortex time: 38 s
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14
Example ll
A procedure similar to that of Comparison Example ll was carried out, except that
after complete neutralization 230 parts of superabsorbent fine-grain particles and,
5 simultaneously, 40 parts of surfactant-containing water were added to the polymer
gel. The nature and amount of the surfactants employed are given in Table ll.
Following the subsequent threefold passage of the gel through the grinder, no fine-
grain agglomerates can be made out in the gel, in contrast to Comparison ExampleIl. The gel mechanically comminuted in this way was dried with hot air at 150C. The
1 0 polymer is subsequently ground and sieved to a particle range of 0.150-0.800 mm.
Table ll
Test Surfactant Parts Retention Vortex time
2 - 1 Tween'l921 2.3 47 9/9 31 s
2 - 2 Genapol~ 2822 4.6 46 9/9 33 s
2 - 3 Hostapur~ SAS 30 0.9 47 9/9 32 s
2 - 4 Sodium lauryl sulfate 1.4 48 9/9 30 s
2 - 5 C12-/C14-Alkylbenzyl- 6.0 47 9/9 35 s
dimethylammonium
chloride
2 - 6 Ampholyt ~JB 130/K 5.1 46 9/9 36 s
Tween 21 (Commercial product from ICI) is polyethylene oxide-(4) sorbitan
monolaurate
Genapol'l9 2822 (Commercial product from Hoechst AG) is a nonionic fatty alcohol-
25 ethylene oxide-propylene oxide adduct.
All products prepared in this test series have a lower vortex time than the product
from Comparison Example ll, i.e. have a more rapid absorbency.
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Example lll
A procedure similar to that of Comparison Example ll was carried out, except that
after complete neutralization 230 parts of superabsorbent fine-grain particles, which
5 had been made up into a paste beforehand with 50 parts of surfactant-containing
water were added to the polymer gel. The nature and amount of the surfactants
employed are given in Table lll. Following the subsequent threefold passage of the
gel through the grinder, no fine-grain agglomerates can be.made out in the gel, in
contrast to Comparison Example ll. The gel mechanically comminuted in this way
10 was dried with hot air at 150C. The polymer is subsequently ground and sieved to a
particle range of 0.150-0.800 mm.
Table lll
Test Surfactant PartsRetention Vortex time
3- 1 SPAN ~20 0.8 49 9l9 28 s
3 - 2 Genapol ~2822 4.0 47 9l9 32 s
3 - 3 PlantarenX 2 000 UPNP 1.0 48 g/g 30 s
3 - 4 Sodium lauryl sulfate 1.2 49 9l9 29 s
3 - 5 C12-/C14-Alkylbenzyldimethyl- 6.4 47 9/9 33 s
ammonium chloride
All products prepared in this test series have a lower vortex time than the product
from Comparison Example ll, i.e. have a more rapid absorbency.
25 Example IV
A procedure similar to that of Comparison Example ll was carried out, except that
after complete neutralization 230 parts of superabsorbent fine-grain particles, which
had been made up into a paste beforehand with 25 parts of surfactant-containing
30 water and, simultaneously, 20 parts of surfactant-containing water were added to
the polymer gel. The nature and amount of the surfactants employed are given in
21 9~373
16
Table IV. Following the subsequent threefold passage of the gel through the grinder,
no fine-grain agglomerates can be made out in the gel, in contrast to ComparisonExample ll. The gel mechanically comminuted in this way was dried with hot air at
150C. The polymer is subsequently ground and sieved to a particle range of 0.150-
0.800 mm.
Table IV
Test Surfactant Parts * Retention Vortex time
4 - 1 Tween 80 2.3 50 9/9 26 s
4 - 2 Genageng~ CA-050 3.2 48 9/9 28 s
4 - 3 Hostapur 3SAS 30 1.2 49 9/9 24 s
4 - 4 Sodium salt of di-(2-ethylhexyl) 1.8 49 9/9 25 s
sulfosuccinate
4 - 5 C12-/C14-Alkylbenzyldimethyl- 5.5 48 9/9 30 s
ammonium chloride
4 - 6 Ampholyt ~JB 130/K 4.0 48 9l9 29 s
* Of the amounts of surfactant indicated, half was added to the water employed for
making up the superabsorbent fine-grain particles into a paste, and the other half
was added to the water added additionally to the polymer gel.
All products prepared in this test series have a lower vortex time than the product
from Comparison Example ll, i.e. have a more rapid absorbency.
Comparison Example lll
A superabsorbent polymer was prepared in accordance with Comparison Example
Il. 3 parts of surfactant-containing water were sprayed onto 100 parts of the ground
and sieved polymer, and the product was subsequently dried at 120C for 1 hour in
a drying oven. The nature and amount of the surfactants employed is given in Table
30 V.
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Table V
Test SurFactant PartsRetention Vortex time
5 -1 Tween ~80 2.3 46 9/9 37 s
5 - 2 Genageng' CA-050 3.2 45 9l9 39 s
5 - 3 Hostapur ~)SAS 30 1.2 45 9l9 38 s
5 - 4 Sodium salt of di-(2- 1.8 44 9/9 37 s
ethylhexyl) sulfosuccinate
5 - 5 C12-/C14-Alkylbenzyldimethyl- 5.5 44 9l9 38 s
ammonium chloride
5 - 6 Ampholyt'l9 JB 1 30/K 4.0 45 9/9 39 s
As is evident from the results of Table V, the products treated with surfactant-containing water show no improvement in the data for retention and vortex time in
comparison with the untreated product from Comparison Example ll. This
demonstrates that the more rapid swelling rates found for the products in Examples
15 Il-IV are based not on an improved wettability of the polymer particles, brought
about by the addition of surfactant, but on the more uniform mixing of the
superabsorbent fine-grain particles into the polymer gels.
