CA2195373A1 - Process for preparing hydrophilic highly swellable hydrogels - Google Patents
Process for preparing hydrophilic highly swellable hydrogelsInfo
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- CA2195373A1 CA2195373A1 CA002195373A CA2195373A CA2195373A1 CA 2195373 A1 CA2195373 A1 CA 2195373A1 CA 002195373 A CA002195373 A CA 002195373A CA 2195373 A CA2195373 A CA 2195373A CA 2195373 A1 CA2195373 A1 CA 2195373A1
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- Prior art keywords
- hydrophilic
- highly swellable
- fine
- gel
- water
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
- C08J3/075—Macromolecular gels
Abstract
The present invention relates to 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 addition of water, wherein the mixing-in operation is carried out in the presence of a surfactant.
Description
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 -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 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 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.
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, 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.
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 o ~
I
j C~ / C~ ~ R
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 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:
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.
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 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 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.
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 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.
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.
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 -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 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 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.
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, 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.
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 o ~
I
j C~ / C~ ~ R
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 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:
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.
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 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 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.
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 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.
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.
Claims (10)
1. 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 addition of water, wherein the mixing-in operation is carried out in the presence of a surfactant.
2. The process as claimed in claim 1, wherein the fine particles have a size of less than 0.1 mm, particularly preferably less than 0.15 mm.
3. The process as claimed in claim 1 and/or 2, wherein the hydrogel in aqueous gel form has a solids content of from 15 to 50% by weight, particularly preferably from 15 to 30% by weight.
4. The process as claimed in one or more of claims 1 to 3, wherein fine-grainparticles and hydrogel in aqueous gel form have the same chemical composition.
5. The process as claimed in one or more of claims 1 to 4, wherein surfactants having a HLB value of greater than or equal to three are used.
6. The process as claimed in one or more of claims 1 to 5, wherein nonionic or anionic surfactants are used.
7. The process as claimed in one or more of claims 1 to 6, wherein the surfactants are used in amounts of from 0.01 to 0.2 part, particularly preferably from 0.015 to 0.15 part, per 100 parts of the hydrophilic highly swellable hydrogel in aqueous gel form.
8. The process as claimed in one or more of claims 1 to 7, wherein hydrophilic highly swellable hydrogels are 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.
9. The process as claimed in claim 8, wherein hydrophilic monomers are compounds of the formula ?
(I) in which R1 is hydrogen, methyl or ethyl, R is the group -COOR4, sulfonyl, phosphonyl, phosphonyl esterified with (C1-C4)-alkanol, or a group of the formula R3 is hydrogen, methyl, ethyl or carboxyl, R4 is hydrogen, amino or hydroxy-(C1-C4)-alkyl, and R5 is sulfonyl, phosphonyl or carboxyl.
(I) in which R1 is hydrogen, methyl or ethyl, R is the group -COOR4, sulfonyl, phosphonyl, phosphonyl esterified with (C1-C4)-alkanol, or a group of the formula R3 is hydrogen, methyl, ethyl or carboxyl, R4 is hydrogen, amino or hydroxy-(C1-C4)-alkyl, and R5 is sulfonyl, phosphonyl or carboxyl.
10. The process as claimed in claim 8 and/or 9, wherein hydrophilic monomers are acrylic acid or methacrylic acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19601764A DE19601764A1 (en) | 1996-01-19 | 1996-01-19 | Process for the production of hydrophilic, highly swellable hydrogels |
| DE19601764.5 | 1996-01-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2195373A1 true CA2195373A1 (en) | 1997-07-20 |
Family
ID=7783128
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195373A Abandoned CA2195373A1 (en) | 1996-01-19 | 1997-01-17 | Process for preparing hydrophilic highly swellable hydrogels |
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| Country | Link |
|---|---|
| EP (1) | EP0785224B1 (en) |
| JP (1) | JP4024894B2 (en) |
| CA (1) | CA2195373A1 (en) |
| DE (2) | DE19601764A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7811605B2 (en) | 2002-11-06 | 2010-10-12 | Uluru Inc. | Method of formation of shape-retentive aggregates of gel particles and their uses |
| US7910135B2 (en) | 2006-10-13 | 2011-03-22 | Uluru Inc. | Hydrogel wound dressing and biomaterials formed in situ and their uses |
| US8080620B2 (en) | 2008-06-19 | 2011-12-20 | Basf Se | Process for continuously producing water-absorbing polymer particles |
| US8410222B2 (en) | 2008-07-15 | 2013-04-02 | Basf Se | Method for producing water-absorbing polymer particles |
| US8765906B2 (en) | 2010-04-27 | 2014-07-01 | Nippon Shokubai, Co., Ltd. | Method for producing polyacrylic acid (salt) type water absorbent resin powder |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7351430B2 (en) * | 2002-11-06 | 2008-04-01 | Uluru Inc. | Shape-retentive hydrogel particle aggregates and their uses |
| US7163966B2 (en) * | 2003-12-19 | 2007-01-16 | Stockhausen, Inc. | Superabsorbent polymer having increased rate of water absorption |
| DE102005014291A1 (en) | 2005-03-24 | 2006-09-28 | Basf Ag | Process for the preparation of water-absorbing polymers |
| WO2012144595A1 (en) | 2011-04-20 | 2012-10-26 | 株式会社日本触媒 | Process and apparatus for producing water-absorbable resin of polyacrylic acid (salt) type |
Family Cites Families (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1301566B (en) | 1966-11-30 | 1969-08-21 | Continental Gummi Werke Ag | Process for the production of hydrolysis-resistant polyurethane elastomers |
| US4057521A (en) | 1974-08-05 | 1977-11-08 | The Dow Chemical Company | Absorbent articles made from carboxylic synthetic polyelectrolytes having copolymerized N-substituted acrylamide crosslinker |
| JPS51125468A (en) | 1975-03-27 | 1976-11-01 | Sanyo Chem Ind Ltd | Method of preparing resins of high water absorbency |
| US4041496A (en) | 1976-04-26 | 1977-08-09 | Norris Paul R | Automatic direction finding system |
| US4062817A (en) | 1977-04-04 | 1977-12-13 | The B.F. Goodrich Company | Water absorbent polymers comprising unsaturated carboxylic acid, acrylic ester containing alkyl group 10-30 carbon atoms, and another acrylic ester containing alkyl group 2-8 carbon atoms |
| US4286082A (en) | 1979-04-06 | 1981-08-25 | Nippon Shokubai Kagaku Kogyo & Co., Ltd. | Absorbent resin composition and process for producing same |
| US4295987A (en) | 1979-12-26 | 1981-10-20 | The Procter & Gamble Company | Cross-linked sodium polyacrylate absorbent |
| JPS6025045B2 (en) | 1980-03-19 | 1985-06-15 | 製鉄化学工業株式会社 | Method for producing acrylic acid polymer with excellent salt water absorption ability |
| US4381782A (en) * | 1981-04-21 | 1983-05-03 | Kimberly-Clark Corporation | Highly absorbent materials having good wicking characteristics which comprise hydrogel particles and surfactant treated filler |
| US4525527A (en) | 1982-01-25 | 1985-06-25 | American Colloid Company | Production process for highly water absorbable polymer |
| DE3738602A1 (en) | 1987-11-13 | 1989-05-24 | Cassella Ag | HYDROPHILY-SOURCE-PURPLE POLYMERISES, THEIR PREPARATION AND USE |
| DE3741157A1 (en) | 1987-12-04 | 1989-06-15 | Stockhausen Chem Fab Gmbh | METHOD FOR THE AGGLOMERATION OF WATER-SOILABLE POLYMER BY MELTING (SINTER) GRANULATION WITH POWDER-SUBSTANCES AND USE OF THE GRANULES |
| DE3817425A1 (en) | 1988-05-21 | 1989-11-23 | Cassella Ag | ALKENYL PHOSPHONE AND PHOSPHINE ACID ESTERS, METHOD FOR THE PRODUCTION THEREOF AND HYDROGELS PRODUCED THEREOF AND THEIR USE |
| US4950692A (en) * | 1988-12-19 | 1990-08-21 | Nalco Chemical Company | Method for reconstituting superabsorbent polymer fines |
| DE3911433A1 (en) | 1989-04-07 | 1990-10-11 | Cassella Ag | HYDROPHILIC SWELLABLE GRAFT POLYMERISATES, THEIR PRODUCTION AND USE |
| US5350799A (en) * | 1990-05-31 | 1994-09-27 | Hoechst Celanese Corporation | Process for the conversion of fine superabsorbent polymer particles into larger particles |
| DE4021847C2 (en) | 1990-07-09 | 1994-09-08 | Stockhausen Chem Fab Gmbh | Process for the preparation of water-swellable products using Feinstanteilen water-swellable polymers |
| US5342899A (en) | 1991-05-16 | 1994-08-30 | The Dow Chemical Company | Process for recycling aqueous fluid absorbents fines to a polymerizer |
-
1996
- 1996-01-19 DE DE19601764A patent/DE19601764A1/en not_active Withdrawn
-
1997
- 1997-01-10 EP EP97100322A patent/EP0785224B1/en not_active Expired - Lifetime
- 1997-01-10 DE DE59709730T patent/DE59709730D1/en not_active Expired - Lifetime
- 1997-01-17 CA CA002195373A patent/CA2195373A1/en not_active Abandoned
- 1997-01-17 JP JP00690797A patent/JP4024894B2/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7811605B2 (en) | 2002-11-06 | 2010-10-12 | Uluru Inc. | Method of formation of shape-retentive aggregates of gel particles and their uses |
| US7910135B2 (en) | 2006-10-13 | 2011-03-22 | Uluru Inc. | Hydrogel wound dressing and biomaterials formed in situ and their uses |
| US8080620B2 (en) | 2008-06-19 | 2011-12-20 | Basf Se | Process for continuously producing water-absorbing polymer particles |
| US8410222B2 (en) | 2008-07-15 | 2013-04-02 | Basf Se | Method for producing water-absorbing polymer particles |
| US8765906B2 (en) | 2010-04-27 | 2014-07-01 | Nippon Shokubai, Co., Ltd. | Method for producing polyacrylic acid (salt) type water absorbent resin powder |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0785224A2 (en) | 1997-07-23 |
| DE59709730D1 (en) | 2003-05-15 |
| JP4024894B2 (en) | 2007-12-19 |
| DE19601764A1 (en) | 1997-07-24 |
| JPH09208710A (en) | 1997-08-12 |
| EP0785224B1 (en) | 2003-04-09 |
| EP0785224A3 (en) | 1998-04-01 |
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