CA1075233A - Highly absorbent modified polysaccharides - Google Patents
Highly absorbent modified polysaccharidesInfo
- Publication number
- CA1075233A CA1075233A CA257,545A CA257545A CA1075233A CA 1075233 A CA1075233 A CA 1075233A CA 257545 A CA257545 A CA 257545A CA 1075233 A CA1075233 A CA 1075233A
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- Prior art keywords
- water
- polysaccharide
- acrylamide
- product
- soluble
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F251/00—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
Abstract
HIGHLY ABSORBENT MODIFIED POLYSACCHARIDES
Abstract of the Disclosure Modified polysaccharides having greatly increased water-absorbing and binding capacity are prepared by reacting a polysac-charide such as cellulose or starch in the presence of acrylamide, another vinyl monomer and a divinyl crosslinking monomer using free radical polymerization techniques. The product is believed to be a complex mixture of crosslinked grafted polysaccharide and acryl-amide copolymers.
Abstract of the Disclosure Modified polysaccharides having greatly increased water-absorbing and binding capacity are prepared by reacting a polysac-charide such as cellulose or starch in the presence of acrylamide, another vinyl monomer and a divinyl crosslinking monomer using free radical polymerization techniques. The product is believed to be a complex mixture of crosslinked grafted polysaccharide and acryl-amide copolymers.
Description
~0~5Z~ A. R. Reid Case 5 This invention relates to novel water-insoluble, hightly ab-sorbent products and to a method of preparing the same. More spe-cifically, it relates to such products based on polysaccharide materials modified via graft polymerization.
In recent years a relatively high level of activity has taken place directed toward the preparation of material of improved ab-sorbency as compared to materials heretofore known. This effort has been particularly vigorous with respect to cellulose and deriv-atives of cellulose, and a number of improvements have been accom-10 plished. For example, cellulose itself, in the form of cottonstaple, cotton linters or wood pulp, can be crosslinked via difunc-tional reagents such as epichlorohydrin to yield relatively small but useful absorbency increases. Dean et al, U.S. patent 3,589,364, teaches that normally water-soluble carboxymethyl cellulose can be crosslinked with epichlorohydrin to form highly absorbent materials.
Elliott, in U.S. 2,639,239, and C~atterjee in U.S. 3,731,686 teach that the conventional water-soluble carboxymethyl cellulose in the Na salt form can be made substantially insoluble in water but highly absorbent by a simple heat treatment. It is also known that partial 20 free acid car~oxymethylcellulo~e forms a more absorbent, substant-ially less soluble material upon being heated. In a very recent development, Chatterjee et al, U.S. 3,889,67~, teaches the prepar-ation of absorbent materials via grafting onto a cellulosic back-bone or host polymer, side chains of a copolymer of acrylonitrile and another nonionic vinyl monomer, followed by hydrolysis to con-vert the acrylonitrile moieties to amide and acrylic acid moieties.
In the preparation of polyacrylonitrile derivatives as taught by Chatterjee et al, considerable ~uantities of free homopolymer are formed. Since these patentees carry out the reaction in sub-30 stantially aqueous medium, this homopolymer is readily separatedand lost during subsequent work-up steps. Moreover, the hydrolysis - step causes more losses of the homopolymer as well as damage ~o the grafted material.
In accordance with this invention, a method of preparin~ a "
grafted product is provided, which method is superior to the method proposed by Chatterjee et al and which results in an improved product. Specifically, it has been found that if the grafting reaction is carried out in a substan-tially water-insoluble medium and in the presence of a water-soluble divinyl compound to effect crosslinking simult~neously with grafting, the amount of separable nongrafted homopolymer is greatly reduced, the hydrolysis step can be eliminated, and a novel product is prepared.
The invention provides a modified polysaccharide which exhibits high absorbency for water and salt solutions and a method of preparing such a modified polysaccharide, which method comprises reacting a water-insoluble, water-swellable polysaccharide s;mllltaneously with acrylamide or methacryl-~mide, at least one other water-soluble monoolefinic vinyl monomer which, in the absence of the polysaccharide, is copolymerizable with acrylamide or methacrylamide to form a water-soluble copolymer, and a water-soluble free radical polymerizable divinyl monomer, in the presence of a free radical catalyst system said reaction being carried out in a reaction medium compris-ing a substantially water-;mm;scible inert liquid diluent having dispersed therein water equal to about 1.5 to 2.5 times the weight of the aforesaid reactants and a low boiling, water-miscible, organic liquid selected which has a low chain transfer constant, in an amount equal to about 25 to 65% of the volume of the aromatic hydrocarbon.
A particularly preferred aspect of the invention is a method of pre-paring a water-insoluble cellulose derivative having high absorbency for water and salt solutions which comprises reacting cellulose or oxidized cellu-lose simultaneously with acrylamide, sodium acrylate and methylene-bis-acrylamide in the presence of a free radical catalyst system, said reaction being carried out in a reaction medium comprised of toluene, water equal to 1.5 to 2.5 times the combined weight of the reactants, and acetone in an amount equal to about 30 to 55% of the volume of the toluene.
1~
Di ~ 3 _ 75'~33 Two critical factors distinguish this invention over the prior art and lead to significantly better results than are accomplished by the prior art. These are (1) use of an inert liquid continuous phase and (2) simul-taneously crosslinking and polymerizing the vinyl monomer. Use of the inert liquid as a continuous phase confines the water phase containing the catalyst components and the vinyl monomers in high concentrations to the water-wettable or water-soluble polysaccharide, thus promoting (a) more efficient conversion of monomer to polymer; (b) more efficient conversion of polysaccharides to radicals suited for grafting; (c) more efficient crosslinking of grafted polysaccharide molecules to synthetic polymer, more efficient crosslinking of grafted polysaccharide molecules to each other and of synthetic polymer mole-cules to each other; and (d) greater entanglement of crosslinked vinyl poly-mer molecules within the polysaccharide matr,ix so that the crosslinked vinyl - 3a -~(~75233 polymer molecules are not easily separated therefrom.
Various water-wettable polysaccharide furnishes in fibrous or powder form can be employed in the process of this invention.
For pur~oses of this discussion, a water-wettable polysaccharide is one which is either insoluble in water or capable of absorbing water and being swollen thereby. These include fibrous cotton and wood pulps, f ine-cut cotton and wood pulps, activated polysaccha-rides such as oxidized cellulose and pre-irradiated celluloses and starches; hydrolyzed polysaccharides such as hydrocelluloses; var-10 ious types of starch such as corn, potato, wheat starches, as is,or pre-gelatinized; guar gum; and various water-insoluble deriva-tives of cellulose, starch, and other polysaccharides such as car-boxymethyl cellulose of D.S. 0.05 to 0.25 and hydroxy ethyl cellu-lose of M.S. 0.05 to 0.25; crosslinked carboxymethyl cellulose of D.S. 0.3 to 1.2, and crosslinked hydroxyethyl cellulose of M.S. 0.3 to 3. Oxidized cellulose and regular cotton an~ wood pulps are preferred.
The presence of the inert water-immiscible diluent as a con-tinuous phase makes a reaction mass of relatively low viscosity 20 which is readily stirrable to improve heat transfer and to improve contact between the vinyl monomers and the polysaccharides. How-ever, since the monomers and catalyst are preferentially soluble in water and the polysaccharide is preferentially wetted by the water, a high concentration of monomers, initiator and activator remains in the water phase and thus in contact with the polysaccharide.
This high concentration of the monomers and activators, confined to the vicinity of the polysaccharide, is believed to be responsible for the high conversion of monomer to crosslinked grafts and for the low incidence of separable synthetic (non-polysaccharide) poly-30 mer. In the absence of the inert water-immiscible diluent reaction medium/ i.e., if water or water plus water-miscible diluent is used as the total reaction medium, the concentration of monomer in the vicinity of each polysaccharide particle is less and products with substantially lower absorption capacity result and the yields thereof are substantially lower.
Substantially any inert, water-immiscible organic liquid can be employed as the reaction medium. By inert is meant that the medium is a nonsolvent for the polysaccharide and the other reac-tants; it is essentially nonreactive with the polysaccharide and other reactants under the conditions existing during the polymer-ization and grafting reaction; and it has a low chain transfer constant under the conditions existing during the said reaction.
The amount of the diluent is not critical so long as there is suf-10 ficient diluent to assure good stirrability and good heat trans-fer, normally about 4 to 8 parts per part of reactants (monomers plus polysaccharide). The preferred class of such materials is the aromatic hydrocarbons, especially toluene. It is found that the best yields and the most highly absorbent products can be pre-pared when the reaction is carried out in toluene.
As suggested by the above, it is desirable to keep the amount of the water relatively low with respect to the reactants so that a relatively high vinyl monomer concentration will be maintained in the vicinity of the polysaccharide particles. To this end only 20 enough watex is used to dissolve the monomers and uniformly wet the polysaccharide, about 1.5 to 2.5 parts per part of reactants.
The vinyl monomers suitable as the second monomer for use in this invention are the water-soluble monoolefinic type containing hydrophilic groups and which, in the absence of thethost polysac-charide, polymerize to form water-soluble homopolymers or copoly-mers with acrylamide or methacrylamide. Such monomers are sub-stantially insoluble in the pxeferred hydrocarbon reaction medium.
Examples of such monomers include acrylic and methacrylic acid and alkali metal salts thereof, alkali metal salts of 2-acryl-30 amido-2-methylpropane sulfonic acid, alkali metal salts of sulfo-propylacrylic acid, 1,2-dimethyl-5-vinylpyridinium methyl sulfate, and 2-(methacroyloxy)-ethyltrimethylammonium methyl sulfate. Pre-ferred vinyl compounds are acrylic acid and the alkali metal salts thereof. The absorption capacity of the grafted, cross-1~7S;c',33 linked polysaccharide-synthetic polymer per unit weight is greater with lower molecular weight vinyl monomers.
The polysaccharide-synthetic polymer grafted product is cross-linked with a divinyl compound which is readily polymerizable via the same free radical mechanisms and catalyst system employed to polymerize the monomers specified above. The crosslinker must also be water-soluble and essentially insoluble in the inert reaction diluent. The preferred crosslinker is methylene-bis-acrylamide (MBA). Other divinyl monomers which can be used as crosslinkers 10 are methylene-bis-methacrylamide and quaternary compounds such as, e.g., quaternized 2,5-divinyl pyridine.
The catalyst systems employed in preparing the graft copoly-mers of this invention are known catalyst materials comprising an inorganic oxidizing agent as an initiator and an inorganic reduc-ing agent as an activator. Any such combination which is water-soluble, which is essentially insoluble in the inert reaction dil-uent, and which is an efficient generator of free radicals in aqueous systems can be employed. Preferred oxidizing agent initi-ators in such combinations are persulfates such as potassium, 20 sodium or ammonium persulfate, and peroxides such as H2O2 and alk-ali metal bromates and chlorates. Preferred reducing agent acti-vators are bisulfites, such as potassium, sodium or ammonium bisul-fite; sulfites such as potassium, sodium or ammonium sulfite; and ferrous iron in the form of such salts as ferrous ammonium sulfate and alkali metal thiosulfates. The preferred redox combination is potassium persulfate and sodium bisulfite. Sufficient catalyst is added to achieve a suitable rate of polymerization and a high mono-mer conversion leading to a high yield of high molecular weight crosslinked grafted polysaccharide-synthetic polymer product in a 39 normal reaction period of 2 to 4 hours. A concentration of initi-ator equal to about 0.2 to 0.4~ and of activator equal to about 0.4 to 0.8%, both based on the weight of the vinyl monomers, is usually sufficient to give the appropriate rate of reaction.
If desired, the reaction can bc carried out without the 1~5'~33 reducing agent present. ~lowever, the lack of reducing agent (act-ivator) must be offset by using higher reaction temperatures;
higher concentration of oxidizing agent, and longer reaction times.
For this reason, the combination catalyst is preferred.
It is also possible to initiate the free radical polymeriza-tion by means of high energy irradiation using, e.g., gamma rays from a cobalt 60 or cesium 137 source or electron beams from a linear accelerator.
As stated hereinabove, it is preferred to have present in the 10 reaction system a low boiling, water-miscible organic diluent which has a low chain transfer constant. This material acts as a precip-itant for the water-soluble polymer formed during the reaction and as a heat transfer fluid to enable reflux operation at a lower temperature than would be possible with water alone to dissipate the heat of reaction. It has also been found, however, that the presence of an appropriate low boiling liquid, in an amount equal to about 2~ to 65~ and preferably about 30 to 55~ of the volume of the inert diluent, leads to higher yields and higher quality pro-ducts than does water alone. Examples of such liquids which are 20 water-miscible and can be employed in the practice of this inven-tion are acetone and isopropanol. The preferred liquid is acetone.
The product which results from carrying out the process of this invention is different in several respects from any product heretofore known to the art. First, the product is highly cross-linked whereas crosslinkers are not used in the preparation of the products of the prior art. More importantly, however, it is a com-plex mixture of grafted polysaccharide and free vinyl homopolymer and/or copolymer containing crosslinkages randomly distributed be-tween grafted polymer side chains, between free homopolymer or co-30 polymer and between grafted polymer side chains and free polymerchains. All or substantially all of the polymer, including the free polymer, is associated in some manner with the polysaccharide and is substantially inseparable therefrom.
The preferred products of the invention contain from about 10 1~7S~3;~
to 60~ by weight of the host polysaccharide and about 40 to 90% by weight of total grafted and free synthetic polymer. The acrylamide component will usually make up about 10 to 50% of the synthetic polymer. Preferably, the host polysaccharide will be about 40 to 50% of the composition with the synthetic polymer being about 50 to 60%. Preferably, the synthetic polymer portion will contain about 20 to 30% of the acrylamide component. Further, the preferre~ pro-ducts contain about 0.2 to 10%, and preferably about 0.5 to 2%, based on the combined weight of monomers, of the div~inyl crosslink-10 ing compound.
The absorbent products of the invention can be used in a va-riety of applications where absorbency is a desideratum. In par-ticular, they are useful in applications such as feminine hygiene products, dental sponges and disposable diapers. Other applications are as moisture barriers, e.g., for underground cables and founda-tions of buildings, for erosion control and as soil conditioners.
An aqueous slurry of the product from chemical cotton or wood pulp furnish can be cast into a film which, on drying, resembles porous paper which can absorb and bind large quantities of water.
The absorbent products can be used alone in any of the above applications. However, for economic reasons, they can be blended with conventional absorbent cellulosics such as crosslinked car-boxymethyl cellulose, chemical cotton, wood pulp or cotton staple.
Relatively small amounts of the invention product can effect rela-tively large increases in absorbency over that of the cellulosic absorbents alone.
Another technique for making use of blends of the invention products and more conventional cellulosics is to coat the conven-tional cellulosics with the invention products. In this method, a 30 grafted, water-insoluble product is slurried in water or aqueous acetone or isopropanol with the conventional cellulosic, followed by treatment with a nonsolvent to depc~-it the grafted product on the surface of the cellulosic in a thin layer. The product is then dehydrated using a water-miscible nonsolvent.
~7S'~33 In the exam~les which follow, the absorbent character of the products is expressed as an estimate of their water-binding capa-city and as a measure of their relative rate of absorbing water and salt solutions. To determine water absorbing capacity, one gram (dry basis) of each product was added rapidly with stirring to 100 and 200 ml. of water in an appropriate bottle. The bottles were cap~ed and then checked at intervals until it appeared no fur-ther absorption was possible. Results are expressed in terms of the gel characteristics of the resultant solution. To determine 10 the relative rate of absorption, 50 and 25 mh. of water and 25 and 20 ml. of 1% NaCl were added to 1 gram (dry basis) of each sample in an appropriate bottle. A timer was started as soon as the liquid contacted the sample and the time required to effect gelling was recorded. This test will be hereafter referred to as the "flood test".
Some of the products were tested for absorbent capacity by means of the so-called "CAP" (capillary or wicking action) test.
The apparatus employed for the CAP test consists of a Buchner fritted glass funnel, with a rubber tube attached to its neck; the 20 tube is attached at the other end to a 50 ml. burette. The burette is filled with the test solution, and the level of liquid is allowed to rise until it just makes contact with the bottom of the frit in the funnel. The level of liquid in the burette can be any-where frorn 0 to 60 cm. below the bottom of this frit. The test sample is placed on top of the frit and a weight exerting a pres-sure of from 0.1 to 0.4 p.s.i. is applied over the entire surface of the sample. The test is then begun and the loss of fluid in the burette is monitored as a function of time to give the rate of ab-sorption. When equilibrium is reached~ the capacity is calculated 30 by dividing the total fluid absorbed at equilibrium, or at the end of 45 minutes, by the weight of the poly~er sample. The conditions used with the CAP test for this work were:
(1) Pressure exerted on the sample was 0.11 p.s.i.
In recent years a relatively high level of activity has taken place directed toward the preparation of material of improved ab-sorbency as compared to materials heretofore known. This effort has been particularly vigorous with respect to cellulose and deriv-atives of cellulose, and a number of improvements have been accom-10 plished. For example, cellulose itself, in the form of cottonstaple, cotton linters or wood pulp, can be crosslinked via difunc-tional reagents such as epichlorohydrin to yield relatively small but useful absorbency increases. Dean et al, U.S. patent 3,589,364, teaches that normally water-soluble carboxymethyl cellulose can be crosslinked with epichlorohydrin to form highly absorbent materials.
Elliott, in U.S. 2,639,239, and C~atterjee in U.S. 3,731,686 teach that the conventional water-soluble carboxymethyl cellulose in the Na salt form can be made substantially insoluble in water but highly absorbent by a simple heat treatment. It is also known that partial 20 free acid car~oxymethylcellulo~e forms a more absorbent, substant-ially less soluble material upon being heated. In a very recent development, Chatterjee et al, U.S. 3,889,67~, teaches the prepar-ation of absorbent materials via grafting onto a cellulosic back-bone or host polymer, side chains of a copolymer of acrylonitrile and another nonionic vinyl monomer, followed by hydrolysis to con-vert the acrylonitrile moieties to amide and acrylic acid moieties.
In the preparation of polyacrylonitrile derivatives as taught by Chatterjee et al, considerable ~uantities of free homopolymer are formed. Since these patentees carry out the reaction in sub-30 stantially aqueous medium, this homopolymer is readily separatedand lost during subsequent work-up steps. Moreover, the hydrolysis - step causes more losses of the homopolymer as well as damage ~o the grafted material.
In accordance with this invention, a method of preparin~ a "
grafted product is provided, which method is superior to the method proposed by Chatterjee et al and which results in an improved product. Specifically, it has been found that if the grafting reaction is carried out in a substan-tially water-insoluble medium and in the presence of a water-soluble divinyl compound to effect crosslinking simult~neously with grafting, the amount of separable nongrafted homopolymer is greatly reduced, the hydrolysis step can be eliminated, and a novel product is prepared.
The invention provides a modified polysaccharide which exhibits high absorbency for water and salt solutions and a method of preparing such a modified polysaccharide, which method comprises reacting a water-insoluble, water-swellable polysaccharide s;mllltaneously with acrylamide or methacryl-~mide, at least one other water-soluble monoolefinic vinyl monomer which, in the absence of the polysaccharide, is copolymerizable with acrylamide or methacrylamide to form a water-soluble copolymer, and a water-soluble free radical polymerizable divinyl monomer, in the presence of a free radical catalyst system said reaction being carried out in a reaction medium compris-ing a substantially water-;mm;scible inert liquid diluent having dispersed therein water equal to about 1.5 to 2.5 times the weight of the aforesaid reactants and a low boiling, water-miscible, organic liquid selected which has a low chain transfer constant, in an amount equal to about 25 to 65% of the volume of the aromatic hydrocarbon.
A particularly preferred aspect of the invention is a method of pre-paring a water-insoluble cellulose derivative having high absorbency for water and salt solutions which comprises reacting cellulose or oxidized cellu-lose simultaneously with acrylamide, sodium acrylate and methylene-bis-acrylamide in the presence of a free radical catalyst system, said reaction being carried out in a reaction medium comprised of toluene, water equal to 1.5 to 2.5 times the combined weight of the reactants, and acetone in an amount equal to about 30 to 55% of the volume of the toluene.
1~
Di ~ 3 _ 75'~33 Two critical factors distinguish this invention over the prior art and lead to significantly better results than are accomplished by the prior art. These are (1) use of an inert liquid continuous phase and (2) simul-taneously crosslinking and polymerizing the vinyl monomer. Use of the inert liquid as a continuous phase confines the water phase containing the catalyst components and the vinyl monomers in high concentrations to the water-wettable or water-soluble polysaccharide, thus promoting (a) more efficient conversion of monomer to polymer; (b) more efficient conversion of polysaccharides to radicals suited for grafting; (c) more efficient crosslinking of grafted polysaccharide molecules to synthetic polymer, more efficient crosslinking of grafted polysaccharide molecules to each other and of synthetic polymer mole-cules to each other; and (d) greater entanglement of crosslinked vinyl poly-mer molecules within the polysaccharide matr,ix so that the crosslinked vinyl - 3a -~(~75233 polymer molecules are not easily separated therefrom.
Various water-wettable polysaccharide furnishes in fibrous or powder form can be employed in the process of this invention.
For pur~oses of this discussion, a water-wettable polysaccharide is one which is either insoluble in water or capable of absorbing water and being swollen thereby. These include fibrous cotton and wood pulps, f ine-cut cotton and wood pulps, activated polysaccha-rides such as oxidized cellulose and pre-irradiated celluloses and starches; hydrolyzed polysaccharides such as hydrocelluloses; var-10 ious types of starch such as corn, potato, wheat starches, as is,or pre-gelatinized; guar gum; and various water-insoluble deriva-tives of cellulose, starch, and other polysaccharides such as car-boxymethyl cellulose of D.S. 0.05 to 0.25 and hydroxy ethyl cellu-lose of M.S. 0.05 to 0.25; crosslinked carboxymethyl cellulose of D.S. 0.3 to 1.2, and crosslinked hydroxyethyl cellulose of M.S. 0.3 to 3. Oxidized cellulose and regular cotton an~ wood pulps are preferred.
The presence of the inert water-immiscible diluent as a con-tinuous phase makes a reaction mass of relatively low viscosity 20 which is readily stirrable to improve heat transfer and to improve contact between the vinyl monomers and the polysaccharides. How-ever, since the monomers and catalyst are preferentially soluble in water and the polysaccharide is preferentially wetted by the water, a high concentration of monomers, initiator and activator remains in the water phase and thus in contact with the polysaccharide.
This high concentration of the monomers and activators, confined to the vicinity of the polysaccharide, is believed to be responsible for the high conversion of monomer to crosslinked grafts and for the low incidence of separable synthetic (non-polysaccharide) poly-30 mer. In the absence of the inert water-immiscible diluent reaction medium/ i.e., if water or water plus water-miscible diluent is used as the total reaction medium, the concentration of monomer in the vicinity of each polysaccharide particle is less and products with substantially lower absorption capacity result and the yields thereof are substantially lower.
Substantially any inert, water-immiscible organic liquid can be employed as the reaction medium. By inert is meant that the medium is a nonsolvent for the polysaccharide and the other reac-tants; it is essentially nonreactive with the polysaccharide and other reactants under the conditions existing during the polymer-ization and grafting reaction; and it has a low chain transfer constant under the conditions existing during the said reaction.
The amount of the diluent is not critical so long as there is suf-10 ficient diluent to assure good stirrability and good heat trans-fer, normally about 4 to 8 parts per part of reactants (monomers plus polysaccharide). The preferred class of such materials is the aromatic hydrocarbons, especially toluene. It is found that the best yields and the most highly absorbent products can be pre-pared when the reaction is carried out in toluene.
As suggested by the above, it is desirable to keep the amount of the water relatively low with respect to the reactants so that a relatively high vinyl monomer concentration will be maintained in the vicinity of the polysaccharide particles. To this end only 20 enough watex is used to dissolve the monomers and uniformly wet the polysaccharide, about 1.5 to 2.5 parts per part of reactants.
The vinyl monomers suitable as the second monomer for use in this invention are the water-soluble monoolefinic type containing hydrophilic groups and which, in the absence of thethost polysac-charide, polymerize to form water-soluble homopolymers or copoly-mers with acrylamide or methacrylamide. Such monomers are sub-stantially insoluble in the pxeferred hydrocarbon reaction medium.
Examples of such monomers include acrylic and methacrylic acid and alkali metal salts thereof, alkali metal salts of 2-acryl-30 amido-2-methylpropane sulfonic acid, alkali metal salts of sulfo-propylacrylic acid, 1,2-dimethyl-5-vinylpyridinium methyl sulfate, and 2-(methacroyloxy)-ethyltrimethylammonium methyl sulfate. Pre-ferred vinyl compounds are acrylic acid and the alkali metal salts thereof. The absorption capacity of the grafted, cross-1~7S;c',33 linked polysaccharide-synthetic polymer per unit weight is greater with lower molecular weight vinyl monomers.
The polysaccharide-synthetic polymer grafted product is cross-linked with a divinyl compound which is readily polymerizable via the same free radical mechanisms and catalyst system employed to polymerize the monomers specified above. The crosslinker must also be water-soluble and essentially insoluble in the inert reaction diluent. The preferred crosslinker is methylene-bis-acrylamide (MBA). Other divinyl monomers which can be used as crosslinkers 10 are methylene-bis-methacrylamide and quaternary compounds such as, e.g., quaternized 2,5-divinyl pyridine.
The catalyst systems employed in preparing the graft copoly-mers of this invention are known catalyst materials comprising an inorganic oxidizing agent as an initiator and an inorganic reduc-ing agent as an activator. Any such combination which is water-soluble, which is essentially insoluble in the inert reaction dil-uent, and which is an efficient generator of free radicals in aqueous systems can be employed. Preferred oxidizing agent initi-ators in such combinations are persulfates such as potassium, 20 sodium or ammonium persulfate, and peroxides such as H2O2 and alk-ali metal bromates and chlorates. Preferred reducing agent acti-vators are bisulfites, such as potassium, sodium or ammonium bisul-fite; sulfites such as potassium, sodium or ammonium sulfite; and ferrous iron in the form of such salts as ferrous ammonium sulfate and alkali metal thiosulfates. The preferred redox combination is potassium persulfate and sodium bisulfite. Sufficient catalyst is added to achieve a suitable rate of polymerization and a high mono-mer conversion leading to a high yield of high molecular weight crosslinked grafted polysaccharide-synthetic polymer product in a 39 normal reaction period of 2 to 4 hours. A concentration of initi-ator equal to about 0.2 to 0.4~ and of activator equal to about 0.4 to 0.8%, both based on the weight of the vinyl monomers, is usually sufficient to give the appropriate rate of reaction.
If desired, the reaction can bc carried out without the 1~5'~33 reducing agent present. ~lowever, the lack of reducing agent (act-ivator) must be offset by using higher reaction temperatures;
higher concentration of oxidizing agent, and longer reaction times.
For this reason, the combination catalyst is preferred.
It is also possible to initiate the free radical polymeriza-tion by means of high energy irradiation using, e.g., gamma rays from a cobalt 60 or cesium 137 source or electron beams from a linear accelerator.
As stated hereinabove, it is preferred to have present in the 10 reaction system a low boiling, water-miscible organic diluent which has a low chain transfer constant. This material acts as a precip-itant for the water-soluble polymer formed during the reaction and as a heat transfer fluid to enable reflux operation at a lower temperature than would be possible with water alone to dissipate the heat of reaction. It has also been found, however, that the presence of an appropriate low boiling liquid, in an amount equal to about 2~ to 65~ and preferably about 30 to 55~ of the volume of the inert diluent, leads to higher yields and higher quality pro-ducts than does water alone. Examples of such liquids which are 20 water-miscible and can be employed in the practice of this inven-tion are acetone and isopropanol. The preferred liquid is acetone.
The product which results from carrying out the process of this invention is different in several respects from any product heretofore known to the art. First, the product is highly cross-linked whereas crosslinkers are not used in the preparation of the products of the prior art. More importantly, however, it is a com-plex mixture of grafted polysaccharide and free vinyl homopolymer and/or copolymer containing crosslinkages randomly distributed be-tween grafted polymer side chains, between free homopolymer or co-30 polymer and between grafted polymer side chains and free polymerchains. All or substantially all of the polymer, including the free polymer, is associated in some manner with the polysaccharide and is substantially inseparable therefrom.
The preferred products of the invention contain from about 10 1~7S~3;~
to 60~ by weight of the host polysaccharide and about 40 to 90% by weight of total grafted and free synthetic polymer. The acrylamide component will usually make up about 10 to 50% of the synthetic polymer. Preferably, the host polysaccharide will be about 40 to 50% of the composition with the synthetic polymer being about 50 to 60%. Preferably, the synthetic polymer portion will contain about 20 to 30% of the acrylamide component. Further, the preferre~ pro-ducts contain about 0.2 to 10%, and preferably about 0.5 to 2%, based on the combined weight of monomers, of the div~inyl crosslink-10 ing compound.
The absorbent products of the invention can be used in a va-riety of applications where absorbency is a desideratum. In par-ticular, they are useful in applications such as feminine hygiene products, dental sponges and disposable diapers. Other applications are as moisture barriers, e.g., for underground cables and founda-tions of buildings, for erosion control and as soil conditioners.
An aqueous slurry of the product from chemical cotton or wood pulp furnish can be cast into a film which, on drying, resembles porous paper which can absorb and bind large quantities of water.
The absorbent products can be used alone in any of the above applications. However, for economic reasons, they can be blended with conventional absorbent cellulosics such as crosslinked car-boxymethyl cellulose, chemical cotton, wood pulp or cotton staple.
Relatively small amounts of the invention product can effect rela-tively large increases in absorbency over that of the cellulosic absorbents alone.
Another technique for making use of blends of the invention products and more conventional cellulosics is to coat the conven-tional cellulosics with the invention products. In this method, a 30 grafted, water-insoluble product is slurried in water or aqueous acetone or isopropanol with the conventional cellulosic, followed by treatment with a nonsolvent to depc~-it the grafted product on the surface of the cellulosic in a thin layer. The product is then dehydrated using a water-miscible nonsolvent.
~7S'~33 In the exam~les which follow, the absorbent character of the products is expressed as an estimate of their water-binding capa-city and as a measure of their relative rate of absorbing water and salt solutions. To determine water absorbing capacity, one gram (dry basis) of each product was added rapidly with stirring to 100 and 200 ml. of water in an appropriate bottle. The bottles were cap~ed and then checked at intervals until it appeared no fur-ther absorption was possible. Results are expressed in terms of the gel characteristics of the resultant solution. To determine 10 the relative rate of absorption, 50 and 25 mh. of water and 25 and 20 ml. of 1% NaCl were added to 1 gram (dry basis) of each sample in an appropriate bottle. A timer was started as soon as the liquid contacted the sample and the time required to effect gelling was recorded. This test will be hereafter referred to as the "flood test".
Some of the products were tested for absorbent capacity by means of the so-called "CAP" (capillary or wicking action) test.
The apparatus employed for the CAP test consists of a Buchner fritted glass funnel, with a rubber tube attached to its neck; the 20 tube is attached at the other end to a 50 ml. burette. The burette is filled with the test solution, and the level of liquid is allowed to rise until it just makes contact with the bottom of the frit in the funnel. The level of liquid in the burette can be any-where frorn 0 to 60 cm. below the bottom of this frit. The test sample is placed on top of the frit and a weight exerting a pres-sure of from 0.1 to 0.4 p.s.i. is applied over the entire surface of the sample. The test is then begun and the loss of fluid in the burette is monitored as a function of time to give the rate of ab-sorption. When equilibrium is reached~ the capacity is calculated 30 by dividing the total fluid absorbed at equilibrium, or at the end of 45 minutes, by the weight of the poly~er sample. The conditions used with the CAP test for this work were:
(1) Pressure exerted on the sample was 0.11 p.s.i.
(2) A11 of the tests were done with the liquid in the _ g _ ~075233 burette 2 cm. below the fritted glass initially. This level was allowed to continually change as absorption occurred.
(3) Pore size of the frit was about 4-5.5 microns.
A complete tabulation of absorbency capacities and rates is pre-sented in Tables 1 and 2 following the Examples.
In determining the vinyl polymer content reported in the ex-amples, it was assumed that all of the polysaccharide raw material was recovered and the following calculation was made:
(Grams polysaccharide x 100) Vinyl Polymer = 100 - (Grams polysaccharide + grams vinyl monomer) % yield Example 1-A
To a 1.5 liter jacketed resin flask equipped with a tap water cooled reflux condenser, pressure-equalizing addition funnels, and a constant rate, high-torque stirring assembly was added 32.4 grams (0.2 mole) of acetone-wet hypochlorite-oxidized cellulose having a theoretical oxygen level of one atom per anhydroglucose unit, 400 20 ml. of toluene and sufficient acetone to bring the total volume up to 200 ml. of acetone. The slurry of oxidized cellulose in a 2/1 by volume mixture of toluene and acetone was stirred for 10 minutes at 25C. At the same time an aqueous monomer solution was prepared as follows: To 110 ml. of water containing 0.06 g. (.00022 mole) of potassium persulfate in the dissolved state was added 15 g.
(0.21 mole) of acrylamide and 0.25 g. (.0016 mole) of N,N'-methyl-enebisacrylamide (MBA~. After the acrylamide and MBA had dissolved 26.9 g. (0.374 mole) of acrylic acid (equivalent to 35 g. of sodium acrylate after neutralization to pH 8.5) was added while cooling 30 the solution in an ice bath. The solution was adjusted to pH 7.5 by slow addition of 50~ NaOH solution with stirring. The a~ueous monomer solution was transferred to a pressure-equalizing addition funnel. The beaker was rinsed with 42 ml. of water and the wash-ings added to the addition funnel. The contents of the funnel were agitated sufficiently to mix the washings uniformly through-out the monomer solution.
The aqueous monomer solution was added to the oxidized cellu-~75Z33 lose slurry in the resin flask dropwise with stirring over about15 minutes, the addition funnel was removed, and stirring was con-tinued for 1 hour at 25C. to allow a uniform impregnation of the oxidized cellulose by the aqueous monomer solution. During this time pressure-equalizing addition funnels containing 0.6% aqueous potassium persulfate solution and 2.3% aqueous sodium bisulfite solution were connected to the resin flask. After the one hour pretreatment at 25C., the system was heated to 50C. (Prior to heat-up, brine solution replaced tap water as the coolant for the 10 reflux condenser.) After stirring for 15 minutes at 50C., the slurry was alternately sparged with nitrogen and evaluated to re-flux through 10 cycles to remove air. With the system under re-flux at 50C., 10 ml. of each of the NaHSO3 and K2S2Og solutions were added over 90 minutes, adding one-millimeter aliquots every 10 minutes. Each NaHSO3 aliquot was followed one minute later by a K2S2O8 aliquot. At a reaction time of 100 minutes another 10 ml.
of NaHSO3 solution was added in increments of 2 ml. every 10 minutes to remove residual persulfate from the system and avoid subsequent contamination of the cellulose-synthetic polymer product 20 with a strong oxidant.
Cooling of the reactor contents was started after a reaction time of 120 minutes, and the system was placed under a slightly positive nitrogen pressure. After 140 minutes when all of the second lot of NaHSO3 solution had been added, the temperature of the reactor was quickly lowered to 25C. Excess liquid was removed via a filter stick, and the product was transferred to a bea~er and washed once with -~1200 ml. of 80 weight per cent aqueous methanol.
In the second wash the slurry was adjusted to pH 8.5 with sodium carbonate solution. The product was then washed sulfate-free with 30 80 weight per cent aqueous methanol. Following excess water remo-val by steeping three times in 95 weight per cent aqueous methanol, excess liquid was removed by vacuum filtration, and the product was dried in vacuo at 60~C. Yield on a dry basis was quantitative based on total starting weight of reactants. The concentration of ~75233 vinyl polymer in the product accordingly was about 61~.
The product in pellet form was ground in a Wiley Micro-mill to different particle sizes. Analysis of the ground material showed a nitrogen content of 3.7%, indicating 28:72 weight per cent acrylamide to sodium acrylate ratio in the grafts and syn-thetic polymer part of the product. This compares to 30 weight per cent acrylamide content of the neutralized monomer blend of acrylamide and sodium acrylate.
Flood test results were obtained on portions of the product 10 ground through 20, 40 and 60 mesh, and comparisons made with ~1) an analogous crosslinked free (i.e., not grafted to polysaccharide) acrylamide-sodium acrylate copolymer prepared from a similar 30:70 weight per cent acrylamide-sodium acrylate monomer blend and an MBA content of 0.5%, based on weight of monomers, and with ~2) finely ground (~ 75% through 60 mesh) epichlorohydrin crosslinked carboxymethyl cellulose prepared essentially as described in U.S.
patent 3,589,364, using fine-cut chemical cotton. Tests at higher liquid to sample ratios of 100/1 and 200/1 were done to determine the approximate absorption capacity of the samples for water. Rates 20 of absorption of water as manifested by gelling time were deter-mined from flood tests employing liquid/sample ratios of 50/1 and 25/1, while rates of absorption of 1% NaCl solution were obtained at liquid/sample weight ratios of 25/1 and 20/1. ~he results shown in Table 1 indicate that the product of this example has a water absorption capacity equal to that of the crosslinked copoly-mer and much higher than that of the crosslinked CMC. Both this example and the copolymer can bind or gel 100 parts of water per part of sample, and almost gel 200 parts of water per part of sample. In contrast, the crosslinked CMC gives low viscosity gel 30 slurries at a water to sample ratio of 100/1, indicating an absorp-tion capacity of much less than 100 ml. of water per gram of sample and probably closer to 40 to 50 ml. of water per gram of sample.
At the lower liquid/sample ratios the gelling times are lower for the invention product and the crosslinked CMC than for the cross-~075Z33 linked copolymer when compared at about the same particle size inwater and 1% NaCl solution, indicating that the invention product and the crosslinked CMC absorb and bind water and 1% NaCl solution faster than the copolymer.
The water absorption capacity of crosslinked CMC is greatly increased by mixing with the product of this Example l-A to make a 50:50 weight per cent blend as shown in Table 1. At water/sample ratios of 50/1, 100 and 200/1, the water-binding power of the blend is much ~reater than that of XLCMC, but lower than that of the in-10 vention by itself. Similarly, the water absorption capacity of fine-cut chemical cotton is increased greatly by mixing with the invention product to make a 50:50 weight per cent blend. However, the rate of binding of 1% NaCl solution by the blend is much in-ferior to that of the invention product.
A 0.5% aqueous slurry of the product of this Example 1-A was cast into a film which on drying resembled a flexible sheet of por-ous paper. The paper had a high water absorption capacity, similar to that of the product in powder form.
Examples l-B, l-C and l-D
The procedure of Example l-A was repeated in triplicate ex-cept that the dried products were ground in a Wiley Intermediate-Mill through 20 mesh. AS shown in Table 1, all three Examples l-B, l-C and l-D absorbed water at liquid/solid ratios of 50/1 and 25/1 and 1% NaC1 solution at liquid/solid ratios of 25/1 and 20/1 faster than did the crosslinked acrylamide-sodium acrylate copolymer. The water absorption capacity of these products was similar to that of Example l-A and the crosslin~ed copolymer.
YieldVinyl Polymer Content Cellulose Con_ent l-B - 100% 61% 39~
l-C - 97% 59% 41%
l-D - 93~ 58% 42%
Example 2 The procedure of Example l-B was repeated except that the M~BA content was 0.25% instead of 0.50~ based on the w~!ight ~ mono-mers. As shown in 1'able 1, this product was not as good as that of Example l-A, l-B, l-C or l-D having a lower rate of absorption (or longer time to qel) at 25/1 in 1~ NaCl solution, and a lower water absorption capacity. Yield = 93%; vinyl polymer content =
58~.
ExamPle 3 The procedure of Example l-B was repeated except that the MBA content was 0.38% instead of 0.50% based on the weight of mono-mers. This product compared favorably with Example l-A, l-B, l-C
and l-D and the crosslinked acrylamide-sodium acrylate copolymer in 10 absorption capacity for water. It gelled faster than the cross-linked copolymer in water at liquid/sample ratios of 50/1 and 25/1 and in 1% NaCl solution at liquid/sample ratios of 25/1 and 20/1, the rate of absorption of liquid by this product being similar to that of the product of Example l-A. Yield = 93%; vinyl polymer content = 58%.
ExamPle 4 The procedure of Example l-B was repeated except that the MBA content was 0.75% based on the weight of monomers. This product was similar to Example l-B in water absorption capacity. However, 20 it was much inferior to Example l-B and the crosslinked copolymer in rate of absorption of 1~ NaCl solution, the gelling times at liquid to sample ratios of 25/1 and 20/1 being very much higher, as shown in Table 1. Yield = 100%; vinyl polymer content = 61%.
Example 5 The procedure of Example l-A was repeated except that the MBA was omitted. The product did not have superabsorbent proper-ties. A 1~ aqueous slurry of this sample had a low ~rookfield vis-cosity of 55 cps. (#2 spindle, 40 r.p.m.) with some material sett-ling out rapidly. The product appeared to be a mixture of products;
30 fine-cut cellulose and grafted pulp which did not swell very much in water and settled out, and a water-soluble low viscosity acryl-amide-sodium acrylate copolymer. Aqueous slurries did not form gels even at lower liquid to sample ratios of 50/1 and 25/1 in water and 25/1 and 20/1 in 1~ NaCl solution. Yield = 88~; vinyl polymer content = 55~.
~75233 Example 6 The procedure of Example l-A was repeated except that toluene was omitted. The toluene was replaced with an equal weight of ace-tone and water to maintain a similar solids (cellulose + monomers) content in the system for comparable stirrability (i.e., 10.5%
solids based on the weight of the system). The yield of product was low (48%) with only ~ 16% conversion of monomers to polymer.
The product did not have superabsorbent properties, being similar to that of Example 5 when dispersed in water or 1% NaCl solution.
ExamPle 7 The procedure of Example l-A was repeated except that the volume ratio of toluene to acetone was changed from 2/1 to 5/1 by replacing 100 ml. of acetone with 100 ml. of toluene. The yield of product was-low (63.5%) with only about 40% conversion of mono-mers to polymer. As shown in Table 1, this product was inferior to that of Example l-A, the portion ground through 20 mesh having a lower water-binding capacity at a liquid to sample ratio of 200/1, a longer time to gel at 50/1, and no gelling up to 10 minutes at 20/1 in 1% NaCl solution.
Exam~le 8 The procedure of Example l-A was repeated except that the volume ratio of toluene to acetone was changed from 2/1 to 1/1 by replacing 100 ml. of toluene with 100 ml. of acetone. This pro-duct was inferior to that of Example l-A having a lower water-absorption capacity than that of Example l-A and was similar to the product of Example 7 when dispersed in 1~ NaCl solution.
Yield = 100~; vinyl polymer content = 61~.
Example 9 The procedure of Example l-B was repeated except that ~1) 30 the activator, NaHSO3, was omitted for the polymerization stage, and (2) the reaction time at 50C. was increased by one hour.
NaHSO3 was added after the end of the reaction period to consume resiclual persulfate. The product compared favora~ly with the group of Example 1-~ C and l-D in water absorption capacity but 1075'~33 was not as ~ood as ~xample l-B in rate of absorption of water at liquid/sample ratios of 50/1 and 25/1 or rate of absorption of 1%
~aCl solution at 25/1 and 20/1. However, at 20/1 in 1% NaCl it is comparable to Examples l-A, l-C and l-D, but inferior to all of them at a liquid to sample ratio of 25/1 in a 1% ~JaCl solution.
Yield = 86%; vinyl polymer content = 54%.
Example 10 The procedure of Example l-A was repeated except that a 70:30 weight per cent acrylamide-sodium acrylate monomer blend was em-10 ployed, and the reaction temperature was 60C. instead of 50C.
This product was inferior to that of Example l-A in water absorp-tion capacity and in rate of absorption in water and 1% l~aCl solu-tion. Yield = 100~; vinyl polymer content = 61%.
ExamPle 11 The procedure of Example l-A was repeated except that unoxi-dized fine-cut chemical cotton furnish was employed. This product compared favorably with that of Example l-A with regard to water absorption capacity and rate of absorption in water and 1% ~aCl solution. Yield = 80%; vinyl polymer content = 51%.
ExamPle 12 The procedure of Examle 11 was repeated except that the temp-erature during the one-hour pretreatment period (i.e., time between addition of the aqueous monomer solution and air removal by alter-nately nitrogen sparging and evacuating to reflux) was increased from 25C. to 50C. This product campared favorably with that of Example l-A in water absorption capacity and rate of binding of water and 1% NaCl solution. Yield of product was 76.5%; vinyl polymer content was 49~.
Although giving good performance in flood tests, this product 30 gave poor results in the CAP test. In this test the initial wet-ting of the product of Example 12 with salt solution resulted in fast hydration and gel for~ation at the liquid-solid interface which drastically reduced further absorption of li~uid by the unwetted product.
iO75Z33 In a Waring Blendor jar containing 400 ml. of water was dis-persed 8 grams of fibrous chemical cotton. To this was added 2 grams of the product of this Example 12. The mixture was asitated vigorously for 5 minutes, left unstirred for 10 minutes, stirred another minute, whereupon the slurry was transferred to a beaker and 800 ml. of acetone was added with stirring. Agitation was con-tinued for an additional 10 minutes. Excess li~uid was decanted and the solid residue was steeped 3 times in 600 ml. of acetone, then excess acetone was removed and the solids were dried in vacuo 10 at 60C. for about 90 minutes.
The CAP test results for this material were significantly better than those for the Example 12 material alone as shown in Table 2. This demonstrates that advantage can be taken of the high absorbent capacity of the material by spreading it thinly as a coating over the surface of a fiber. Formation of a continuous concentrated gel network at the water-liquid solid interface is avoided upon wetting, while the good wicking action of the fibrous furnish is substantially retained.
Example 13 The procedure of ~xample 12 was repeated except the quantity of MBA was increased from 0.5% to 2.0% based on weight of monomers.
This more highly crosslinked product was much inferior to that of Example 12 in water absorption capacity giving a low viscosity gel slurry at a water/sample ratio of 200/1 whereas the product of Ex-ample 12 was almost gelled at this ratio. The product compared favorably with that of Example 12 at water/samp~e ratios of 100/1, 50/1 and 25/1, but was very much inferior with regard to rate of bin~ing of 1% NaCl solution. As shown in Table 1, this product did not gel 1% NaCl solution even in 10 minutes. This lack of gelling 30 of 1% NaCl solution ~i.e., reduced rate of hydration in this system) is reflected in greatly improved CAP test results compared to the product of Example 12, as shown in Table 2. The reduced rate of hy-dration is most likely a result of the greater degree of crosslink-ing in this sample compared to that of the Example 12 product.
~75;~33 Yield = 94~; vinyl polymer content = 58~.
Example 14 The procedure of Example 12 was repeated except that the quan-tity of MBA was increased from O.S to 10% based on weight of mono-mers. Yield = 82%; vinyl polymer content = 52%.
As shown in Table 1, this highly crosslinked product performed poorly in flood test~, exhibiting a much lower water absorption capacity and rate of absorption of water and 1% NaCl solution than Example 12. This product gave low viscosity gel slurries in water 1~ at liquid/sample ratios of 200/1, 100/1 and 50/1, and in 1% NaCl solution at liquid/sample ratios of 25/1 and 20/1. No gelling was observed in 10 minute~ even at a low water/sample ratio of 25/1.
However, the much lower rate of hydration of this product in 1%
NaCl solution led to much better CAP test results than observed with the product of Example 12 as shown in Table 2.
Exam~le lS
The procedure of Example 12 was repeated except that MBA was omitted. Yield = 91%; vinyl polymer content = 57~. This product did not have superabsorbent properties, being similar to that of 20 Example 5.
Exam~le 16 The procedure of Example 12 was repeated except that the acryl-amide was replaced with an equimolar quantity of sodium acrylate in the aqueous monomer solution. The yield of product was low (49%) with only about 16% of the monomers converted to polymer. As shown in Table 1, this product was much poorer in water absorption capa-city than that of Example 12, although comparable in rate of gel-ling at a water/sample ratio of 25/1. It was inferior to the pro-duct of Example 12 in rate of binding of 1% NaCl solution at a 30 liquid/sample ratio of 20/1, no gelling being observed up to 12 minutes after contact of the product with the salt solution.
Example 17 The procedure of Example 12 was repeated except that the tolu-ene was replaced with an equal volume of benzene. This product was ~)75Z33 similar to that of Example 12 in water absorption capacity and rateof gelling of water and 1% NaCl solution. Yield = 69%; vinyl poly-mer content = 43~.
Example 18 The procedure of Example 12 was repeated ex~ept that the fine-cut chemical cotton was replaced with long-fiber staple cotton. The use of the long-fiber furnish required an increase from 400 ml. to 600 ml. of toluene and from 200 ml. to 300 ml. of acetone to ac-hieve adequate stirring and keep the toluene/acetone ratio at 2/1 10 as with Example 12. Also, all of the potassium persulfate required for the polymerization was added to the aqueous monomer solution prior to dropwise addition to the cotton in toluene-acetone slurry.
No activator was added during polymerization. However, some NaHSO3 was added after reaction, as usual, to remove residual persulfate.
Yield = 74%; vinyl polymer content = 47%. The knotted fiber prod-uct was hammer-milled in order to break apart matted fiber clusters with a minimum of fiber cutting.
This f~brous sample was comparable to that of Example 12 in water absorption and rate of gelling in water. However, at a 20 liquid/sarnple ratio of 25/1 this product gelled 1% NaCl solution faster than any other sample tested, and at a ratio of 20/1 was comparable to the product of Example l-B. As shown in Table 2, this product gave a much better performance in the CAP test than that of Example 12, most likely because of its fibrous nature.
Example 19 The procedure of Example 12 was repeated except that the fine-cut chemical cotton furnish was replaced by a gelatinized wheat starch. As shown in Table 1, this product is comparable to that of Example 12 in water absorption capacity, but is inferior to that 30 of Exam~le 12 in the rate of binding or gelling of water at liquid/
sample ratios of 50~1 and 25/1 and of 1% NaCl solution at ratios of 25/1 and 20/1. Yield - 82% vinyl polymer content = 52~.
Example 20 The procedure of ~xample 12 was repeated except that the fine--- lg --~37S;~33 cut chemical cotton was replaced by a corn starch furnish. Yield= 83%; vinyl polymer content = 53%.
This product compared favorably with that of Example 12 in water absorption capacity and rate of gelling of water, but was in-ferior in rate of binding 1% NaCl solution.
Example 21 The procedure of Example 12 was repeated except that the fine-cut chemical cotton was replaced by guar gum. Yield = 81%; vinyl polymer content = 51%.
This product had a lower water-binding capacity at a liquid/
sample ratio of 200/1, and a slower rate of absorption of water than that of Example 12. This product compared favorably with that of Example 12 in rate of gelling of 1% NaCl solution at a liquid to sample ratio of 20/1.
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~075233 Tab,e 1 Footnotes la~ AG = almost gelled; G = gelled; LVGS, MVGS, HVGS = low, medium and high viscosity gel slurries, respectively; NG = not gelled; all samples through 20 mesh unless otherwise speci-fied.
(b) Acrylamide-sodium acrylate ~30:70 wt. %) copolymer crosslinked with 0.5% MBA based on nomer weight.
(c) Epichlorohydrin crosslinked carboxymethyl cellulose (XL CMC) having 0.7 D.S. ( _759~ through 60 mesh) 10 (d) 50:50 wt. % blend of Example l-A and fine-cut chemical cotton (e) 50:50 wt. % blend of Example l-A and XL CMC.
Table 2 CAP Test Data on Crosslinked Cellulose-Svnthetic Polymer Products Absorption Per Time Interval*
Sample 1 3 5 10 15 20 25 30 35 40 45 Example 12 0.40.60.71.01.11.3 1.4 1.5 1.6 1.7 1.8 Fibrous Chemi- 0.81.92.83.74.34.5 4.5 4.5 cal Cotton (FCC) FCC coated with 0.92.33.55.46.16.4 6.5 6.5 6.5 2596 Of Example 12 by weight Example 13 1.11.92.53.74.65.4 6.1 6.6 7.0 7.5 7.7 Example 14 2.04.05.26.46.56.5 6.5 Staple Cotton 0.40.60.81.11.41.6 1.8 2.0 2.1 2.2 2.3 Example 18 1.02.33.45.77.58.2 8.6 8.8 8.9 9.0 9.0 *Absorption of 1% NaCl solution ~ml./g. of sample) at vario~s times in minutes ExamDle 22 Using the procedure substantially as described in Example l-A, 30 a fibrous chemical cotton was reacted in 570 ml. of toluene and 200 ml. of acetone with a 50/50 by weight mixture of acrylamide and sodium acrylate. The cataIyst additions comprised 0.1 g. aliquot of potassium persulfate and 0.4 g. aliquots of activator. The yield of product was quantitative; vinyl polymer content - 6196.
The product of this reaction was ground in a Wiley intermedi-ate mil7 to 20 mesh particle size. Analysis of the ground material showed a nitrogen content of 6.3596 indicating that the acrylamide to sodium acrylate ratio in the product was 45:55. The product compared favorably with Example 1-B in the water absorption capacity 40 and was slightly slower in rate of water absorption at liquid to solid ratios of 50:1 and 25:1. It was inferior to Example 1-~ in ~075233 rate of absorption of 1~ sodium chloride solution at liquid to solid ratios of 25:1 and 20:1.
Example 23 One gram of the material from Example l-B as it came from the reactor in pellet form and one gram of the same material after be-ing ground through 20 mesh were slurried in 500 ml. portions of distilled water. After standing for 48 hours at room temperature, the gels were collected on tared fluted filter papers. After draining over a wee~end in a closed system, the amount of water 10 drained from the ground sample was 248 g. and from the unground sample 255 g.
The gel from the 20-mesh material was dried in a forced draft oven at 105C. for 4 hours followed by 18 hours at 100C. in a con-vection oven. The weight of product recovered was 0.95 g. indica-ting only 5~ loss from extraction and handling.
The gel from the unground material was washed three times with acetone, then dried four hours at 60C. in vacuo followed by 18 hours at 100C. in a convection oven. The weight of product recovered was one gram, indicating no loss from extraction and 20 handling.
ExamPle 24 Two one-gram lots of the product of Example 5 (dry basis), ground through 20 mesh, were slurried in 500 ml. of distilled water. After standing 24 hours at room temperature, the slightly viscous supernatant liquid was separated from the insoluble material by careful decantation. The water-insoluble material was slurried in 500 ml. of acetone and left standing at room tempera-ture over a weekend. The difficultly filterahle supernatant liquid was filtered through tared fluted filter papers in a closed system 30 over a period of seven days. The amount of liquid drained throu~h the filters in this time was 440 ml. in one case and 445 ml. in the other. The filter papers were dried 18 hours at 100C. in a con-vection oven and found to have lost 0.06 g. in weight in each case, indicating that substantially no water-insoluble material was ~(~75f~3;~
present in the supernatant liquid passed through the filter papers.
Excess acetone was removed from the above acetone slurries ofthe water-insoluble material and the solids washed twice more with acetone to remove water. After removal of excess acetone, the solids were dried in vacuo at 60C. followed by la hours at 100C.
in a convection oven. The weight of recovered water-insoluble material was 0.38 g. in each case, indicating a 62% loss from ex-traction and handling.
A complete tabulation of absorbency capacities and rates is pre-sented in Tables 1 and 2 following the Examples.
In determining the vinyl polymer content reported in the ex-amples, it was assumed that all of the polysaccharide raw material was recovered and the following calculation was made:
(Grams polysaccharide x 100) Vinyl Polymer = 100 - (Grams polysaccharide + grams vinyl monomer) % yield Example 1-A
To a 1.5 liter jacketed resin flask equipped with a tap water cooled reflux condenser, pressure-equalizing addition funnels, and a constant rate, high-torque stirring assembly was added 32.4 grams (0.2 mole) of acetone-wet hypochlorite-oxidized cellulose having a theoretical oxygen level of one atom per anhydroglucose unit, 400 20 ml. of toluene and sufficient acetone to bring the total volume up to 200 ml. of acetone. The slurry of oxidized cellulose in a 2/1 by volume mixture of toluene and acetone was stirred for 10 minutes at 25C. At the same time an aqueous monomer solution was prepared as follows: To 110 ml. of water containing 0.06 g. (.00022 mole) of potassium persulfate in the dissolved state was added 15 g.
(0.21 mole) of acrylamide and 0.25 g. (.0016 mole) of N,N'-methyl-enebisacrylamide (MBA~. After the acrylamide and MBA had dissolved 26.9 g. (0.374 mole) of acrylic acid (equivalent to 35 g. of sodium acrylate after neutralization to pH 8.5) was added while cooling 30 the solution in an ice bath. The solution was adjusted to pH 7.5 by slow addition of 50~ NaOH solution with stirring. The a~ueous monomer solution was transferred to a pressure-equalizing addition funnel. The beaker was rinsed with 42 ml. of water and the wash-ings added to the addition funnel. The contents of the funnel were agitated sufficiently to mix the washings uniformly through-out the monomer solution.
The aqueous monomer solution was added to the oxidized cellu-~75Z33 lose slurry in the resin flask dropwise with stirring over about15 minutes, the addition funnel was removed, and stirring was con-tinued for 1 hour at 25C. to allow a uniform impregnation of the oxidized cellulose by the aqueous monomer solution. During this time pressure-equalizing addition funnels containing 0.6% aqueous potassium persulfate solution and 2.3% aqueous sodium bisulfite solution were connected to the resin flask. After the one hour pretreatment at 25C., the system was heated to 50C. (Prior to heat-up, brine solution replaced tap water as the coolant for the 10 reflux condenser.) After stirring for 15 minutes at 50C., the slurry was alternately sparged with nitrogen and evaluated to re-flux through 10 cycles to remove air. With the system under re-flux at 50C., 10 ml. of each of the NaHSO3 and K2S2Og solutions were added over 90 minutes, adding one-millimeter aliquots every 10 minutes. Each NaHSO3 aliquot was followed one minute later by a K2S2O8 aliquot. At a reaction time of 100 minutes another 10 ml.
of NaHSO3 solution was added in increments of 2 ml. every 10 minutes to remove residual persulfate from the system and avoid subsequent contamination of the cellulose-synthetic polymer product 20 with a strong oxidant.
Cooling of the reactor contents was started after a reaction time of 120 minutes, and the system was placed under a slightly positive nitrogen pressure. After 140 minutes when all of the second lot of NaHSO3 solution had been added, the temperature of the reactor was quickly lowered to 25C. Excess liquid was removed via a filter stick, and the product was transferred to a bea~er and washed once with -~1200 ml. of 80 weight per cent aqueous methanol.
In the second wash the slurry was adjusted to pH 8.5 with sodium carbonate solution. The product was then washed sulfate-free with 30 80 weight per cent aqueous methanol. Following excess water remo-val by steeping three times in 95 weight per cent aqueous methanol, excess liquid was removed by vacuum filtration, and the product was dried in vacuo at 60~C. Yield on a dry basis was quantitative based on total starting weight of reactants. The concentration of ~75233 vinyl polymer in the product accordingly was about 61~.
The product in pellet form was ground in a Wiley Micro-mill to different particle sizes. Analysis of the ground material showed a nitrogen content of 3.7%, indicating 28:72 weight per cent acrylamide to sodium acrylate ratio in the grafts and syn-thetic polymer part of the product. This compares to 30 weight per cent acrylamide content of the neutralized monomer blend of acrylamide and sodium acrylate.
Flood test results were obtained on portions of the product 10 ground through 20, 40 and 60 mesh, and comparisons made with ~1) an analogous crosslinked free (i.e., not grafted to polysaccharide) acrylamide-sodium acrylate copolymer prepared from a similar 30:70 weight per cent acrylamide-sodium acrylate monomer blend and an MBA content of 0.5%, based on weight of monomers, and with ~2) finely ground (~ 75% through 60 mesh) epichlorohydrin crosslinked carboxymethyl cellulose prepared essentially as described in U.S.
patent 3,589,364, using fine-cut chemical cotton. Tests at higher liquid to sample ratios of 100/1 and 200/1 were done to determine the approximate absorption capacity of the samples for water. Rates 20 of absorption of water as manifested by gelling time were deter-mined from flood tests employing liquid/sample ratios of 50/1 and 25/1, while rates of absorption of 1% NaCl solution were obtained at liquid/sample weight ratios of 25/1 and 20/1. ~he results shown in Table 1 indicate that the product of this example has a water absorption capacity equal to that of the crosslinked copoly-mer and much higher than that of the crosslinked CMC. Both this example and the copolymer can bind or gel 100 parts of water per part of sample, and almost gel 200 parts of water per part of sample. In contrast, the crosslinked CMC gives low viscosity gel 30 slurries at a water to sample ratio of 100/1, indicating an absorp-tion capacity of much less than 100 ml. of water per gram of sample and probably closer to 40 to 50 ml. of water per gram of sample.
At the lower liquid/sample ratios the gelling times are lower for the invention product and the crosslinked CMC than for the cross-~075Z33 linked copolymer when compared at about the same particle size inwater and 1% NaCl solution, indicating that the invention product and the crosslinked CMC absorb and bind water and 1% NaCl solution faster than the copolymer.
The water absorption capacity of crosslinked CMC is greatly increased by mixing with the product of this Example l-A to make a 50:50 weight per cent blend as shown in Table 1. At water/sample ratios of 50/1, 100 and 200/1, the water-binding power of the blend is much ~reater than that of XLCMC, but lower than that of the in-10 vention by itself. Similarly, the water absorption capacity of fine-cut chemical cotton is increased greatly by mixing with the invention product to make a 50:50 weight per cent blend. However, the rate of binding of 1% NaCl solution by the blend is much in-ferior to that of the invention product.
A 0.5% aqueous slurry of the product of this Example 1-A was cast into a film which on drying resembled a flexible sheet of por-ous paper. The paper had a high water absorption capacity, similar to that of the product in powder form.
Examples l-B, l-C and l-D
The procedure of Example l-A was repeated in triplicate ex-cept that the dried products were ground in a Wiley Intermediate-Mill through 20 mesh. AS shown in Table 1, all three Examples l-B, l-C and l-D absorbed water at liquid/solid ratios of 50/1 and 25/1 and 1% NaC1 solution at liquid/solid ratios of 25/1 and 20/1 faster than did the crosslinked acrylamide-sodium acrylate copolymer. The water absorption capacity of these products was similar to that of Example l-A and the crosslin~ed copolymer.
YieldVinyl Polymer Content Cellulose Con_ent l-B - 100% 61% 39~
l-C - 97% 59% 41%
l-D - 93~ 58% 42%
Example 2 The procedure of Example l-B was repeated except that the M~BA content was 0.25% instead of 0.50~ based on the w~!ight ~ mono-mers. As shown in 1'able 1, this product was not as good as that of Example l-A, l-B, l-C or l-D having a lower rate of absorption (or longer time to qel) at 25/1 in 1~ NaCl solution, and a lower water absorption capacity. Yield = 93%; vinyl polymer content =
58~.
ExamPle 3 The procedure of Example l-B was repeated except that the MBA content was 0.38% instead of 0.50% based on the weight of mono-mers. This product compared favorably with Example l-A, l-B, l-C
and l-D and the crosslinked acrylamide-sodium acrylate copolymer in 10 absorption capacity for water. It gelled faster than the cross-linked copolymer in water at liquid/sample ratios of 50/1 and 25/1 and in 1% NaCl solution at liquid/sample ratios of 25/1 and 20/1, the rate of absorption of liquid by this product being similar to that of the product of Example l-A. Yield = 93%; vinyl polymer content = 58%.
ExamPle 4 The procedure of Example l-B was repeated except that the MBA content was 0.75% based on the weight of monomers. This product was similar to Example l-B in water absorption capacity. However, 20 it was much inferior to Example l-B and the crosslinked copolymer in rate of absorption of 1~ NaCl solution, the gelling times at liquid to sample ratios of 25/1 and 20/1 being very much higher, as shown in Table 1. Yield = 100%; vinyl polymer content = 61%.
Example 5 The procedure of Example l-A was repeated except that the MBA was omitted. The product did not have superabsorbent proper-ties. A 1~ aqueous slurry of this sample had a low ~rookfield vis-cosity of 55 cps. (#2 spindle, 40 r.p.m.) with some material sett-ling out rapidly. The product appeared to be a mixture of products;
30 fine-cut cellulose and grafted pulp which did not swell very much in water and settled out, and a water-soluble low viscosity acryl-amide-sodium acrylate copolymer. Aqueous slurries did not form gels even at lower liquid to sample ratios of 50/1 and 25/1 in water and 25/1 and 20/1 in 1~ NaCl solution. Yield = 88~; vinyl polymer content = 55~.
~75233 Example 6 The procedure of Example l-A was repeated except that toluene was omitted. The toluene was replaced with an equal weight of ace-tone and water to maintain a similar solids (cellulose + monomers) content in the system for comparable stirrability (i.e., 10.5%
solids based on the weight of the system). The yield of product was low (48%) with only ~ 16% conversion of monomers to polymer.
The product did not have superabsorbent properties, being similar to that of Example 5 when dispersed in water or 1% NaCl solution.
ExamPle 7 The procedure of Example l-A was repeated except that the volume ratio of toluene to acetone was changed from 2/1 to 5/1 by replacing 100 ml. of acetone with 100 ml. of toluene. The yield of product was-low (63.5%) with only about 40% conversion of mono-mers to polymer. As shown in Table 1, this product was inferior to that of Example l-A, the portion ground through 20 mesh having a lower water-binding capacity at a liquid to sample ratio of 200/1, a longer time to gel at 50/1, and no gelling up to 10 minutes at 20/1 in 1% NaCl solution.
Exam~le 8 The procedure of Example l-A was repeated except that the volume ratio of toluene to acetone was changed from 2/1 to 1/1 by replacing 100 ml. of toluene with 100 ml. of acetone. This pro-duct was inferior to that of Example l-A having a lower water-absorption capacity than that of Example l-A and was similar to the product of Example 7 when dispersed in 1~ NaCl solution.
Yield = 100~; vinyl polymer content = 61~.
Example 9 The procedure of Example l-B was repeated except that ~1) 30 the activator, NaHSO3, was omitted for the polymerization stage, and (2) the reaction time at 50C. was increased by one hour.
NaHSO3 was added after the end of the reaction period to consume resiclual persulfate. The product compared favora~ly with the group of Example 1-~ C and l-D in water absorption capacity but 1075'~33 was not as ~ood as ~xample l-B in rate of absorption of water at liquid/sample ratios of 50/1 and 25/1 or rate of absorption of 1%
~aCl solution at 25/1 and 20/1. However, at 20/1 in 1% NaCl it is comparable to Examples l-A, l-C and l-D, but inferior to all of them at a liquid to sample ratio of 25/1 in a 1% ~JaCl solution.
Yield = 86%; vinyl polymer content = 54%.
Example 10 The procedure of Example l-A was repeated except that a 70:30 weight per cent acrylamide-sodium acrylate monomer blend was em-10 ployed, and the reaction temperature was 60C. instead of 50C.
This product was inferior to that of Example l-A in water absorp-tion capacity and in rate of absorption in water and 1% l~aCl solu-tion. Yield = 100~; vinyl polymer content = 61%.
ExamPle 11 The procedure of Example l-A was repeated except that unoxi-dized fine-cut chemical cotton furnish was employed. This product compared favorably with that of Example l-A with regard to water absorption capacity and rate of absorption in water and 1% ~aCl solution. Yield = 80%; vinyl polymer content = 51%.
ExamPle 12 The procedure of Examle 11 was repeated except that the temp-erature during the one-hour pretreatment period (i.e., time between addition of the aqueous monomer solution and air removal by alter-nately nitrogen sparging and evacuating to reflux) was increased from 25C. to 50C. This product campared favorably with that of Example l-A in water absorption capacity and rate of binding of water and 1% NaCl solution. Yield of product was 76.5%; vinyl polymer content was 49~.
Although giving good performance in flood tests, this product 30 gave poor results in the CAP test. In this test the initial wet-ting of the product of Example 12 with salt solution resulted in fast hydration and gel for~ation at the liquid-solid interface which drastically reduced further absorption of li~uid by the unwetted product.
iO75Z33 In a Waring Blendor jar containing 400 ml. of water was dis-persed 8 grams of fibrous chemical cotton. To this was added 2 grams of the product of this Example 12. The mixture was asitated vigorously for 5 minutes, left unstirred for 10 minutes, stirred another minute, whereupon the slurry was transferred to a beaker and 800 ml. of acetone was added with stirring. Agitation was con-tinued for an additional 10 minutes. Excess li~uid was decanted and the solid residue was steeped 3 times in 600 ml. of acetone, then excess acetone was removed and the solids were dried in vacuo 10 at 60C. for about 90 minutes.
The CAP test results for this material were significantly better than those for the Example 12 material alone as shown in Table 2. This demonstrates that advantage can be taken of the high absorbent capacity of the material by spreading it thinly as a coating over the surface of a fiber. Formation of a continuous concentrated gel network at the water-liquid solid interface is avoided upon wetting, while the good wicking action of the fibrous furnish is substantially retained.
Example 13 The procedure of ~xample 12 was repeated except the quantity of MBA was increased from 0.5% to 2.0% based on weight of monomers.
This more highly crosslinked product was much inferior to that of Example 12 in water absorption capacity giving a low viscosity gel slurry at a water/sample ratio of 200/1 whereas the product of Ex-ample 12 was almost gelled at this ratio. The product compared favorably with that of Example 12 at water/samp~e ratios of 100/1, 50/1 and 25/1, but was very much inferior with regard to rate of bin~ing of 1% NaCl solution. As shown in Table 1, this product did not gel 1% NaCl solution even in 10 minutes. This lack of gelling 30 of 1% NaCl solution ~i.e., reduced rate of hydration in this system) is reflected in greatly improved CAP test results compared to the product of Example 12, as shown in Table 2. The reduced rate of hy-dration is most likely a result of the greater degree of crosslink-ing in this sample compared to that of the Example 12 product.
~75;~33 Yield = 94~; vinyl polymer content = 58~.
Example 14 The procedure of Example 12 was repeated except that the quan-tity of MBA was increased from O.S to 10% based on weight of mono-mers. Yield = 82%; vinyl polymer content = 52%.
As shown in Table 1, this highly crosslinked product performed poorly in flood test~, exhibiting a much lower water absorption capacity and rate of absorption of water and 1% NaCl solution than Example 12. This product gave low viscosity gel slurries in water 1~ at liquid/sample ratios of 200/1, 100/1 and 50/1, and in 1% NaCl solution at liquid/sample ratios of 25/1 and 20/1. No gelling was observed in 10 minute~ even at a low water/sample ratio of 25/1.
However, the much lower rate of hydration of this product in 1%
NaCl solution led to much better CAP test results than observed with the product of Example 12 as shown in Table 2.
Exam~le lS
The procedure of Example 12 was repeated except that MBA was omitted. Yield = 91%; vinyl polymer content = 57~. This product did not have superabsorbent properties, being similar to that of 20 Example 5.
Exam~le 16 The procedure of Example 12 was repeated except that the acryl-amide was replaced with an equimolar quantity of sodium acrylate in the aqueous monomer solution. The yield of product was low (49%) with only about 16% of the monomers converted to polymer. As shown in Table 1, this product was much poorer in water absorption capa-city than that of Example 12, although comparable in rate of gel-ling at a water/sample ratio of 25/1. It was inferior to the pro-duct of Example 12 in rate of binding of 1% NaCl solution at a 30 liquid/sample ratio of 20/1, no gelling being observed up to 12 minutes after contact of the product with the salt solution.
Example 17 The procedure of Example 12 was repeated except that the tolu-ene was replaced with an equal volume of benzene. This product was ~)75Z33 similar to that of Example 12 in water absorption capacity and rateof gelling of water and 1% NaCl solution. Yield = 69%; vinyl poly-mer content = 43~.
Example 18 The procedure of Example 12 was repeated ex~ept that the fine-cut chemical cotton was replaced with long-fiber staple cotton. The use of the long-fiber furnish required an increase from 400 ml. to 600 ml. of toluene and from 200 ml. to 300 ml. of acetone to ac-hieve adequate stirring and keep the toluene/acetone ratio at 2/1 10 as with Example 12. Also, all of the potassium persulfate required for the polymerization was added to the aqueous monomer solution prior to dropwise addition to the cotton in toluene-acetone slurry.
No activator was added during polymerization. However, some NaHSO3 was added after reaction, as usual, to remove residual persulfate.
Yield = 74%; vinyl polymer content = 47%. The knotted fiber prod-uct was hammer-milled in order to break apart matted fiber clusters with a minimum of fiber cutting.
This f~brous sample was comparable to that of Example 12 in water absorption and rate of gelling in water. However, at a 20 liquid/sarnple ratio of 25/1 this product gelled 1% NaCl solution faster than any other sample tested, and at a ratio of 20/1 was comparable to the product of Example l-B. As shown in Table 2, this product gave a much better performance in the CAP test than that of Example 12, most likely because of its fibrous nature.
Example 19 The procedure of Example 12 was repeated except that the fine-cut chemical cotton furnish was replaced by a gelatinized wheat starch. As shown in Table 1, this product is comparable to that of Example 12 in water absorption capacity, but is inferior to that 30 of Exam~le 12 in the rate of binding or gelling of water at liquid/
sample ratios of 50~1 and 25/1 and of 1% NaCl solution at ratios of 25/1 and 20/1. Yield - 82% vinyl polymer content = 52~.
Example 20 The procedure of ~xample 12 was repeated except that the fine--- lg --~37S;~33 cut chemical cotton was replaced by a corn starch furnish. Yield= 83%; vinyl polymer content = 53%.
This product compared favorably with that of Example 12 in water absorption capacity and rate of gelling of water, but was in-ferior in rate of binding 1% NaCl solution.
Example 21 The procedure of Example 12 was repeated except that the fine-cut chemical cotton was replaced by guar gum. Yield = 81%; vinyl polymer content = 51%.
This product had a lower water-binding capacity at a liquid/
sample ratio of 200/1, and a slower rate of absorption of water than that of Example 12. This product compared favorably with that of Example 12 in rate of gelling of 1% NaCl solution at a liquid to sample ratio of 20/1.
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1~ V V ~!) V t!) V U- V ~ Z V z t~ V V ~j zV V V V V V ~
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~1 rl U~
V
O
~q ~1 O
~ l ~v ~ ~ ~ ~ V ~ V ~ v ~v ~v ~v --~ U ~
al o--~ âJ
~ ~mo~ o~
1~ _I ~ ~1 _1 C~ U '~ ~, N ') ~ It') ~D t` 00 ~ O ~I N ~ ~ Ir) ID t~ O ~ N
X ~-1 ~ ~ ~ '--I ~1--I '~ '--I '-I ~1 ~1 ~ ~--1 ~ N N
X X ~1 ~
~075233 Tab,e 1 Footnotes la~ AG = almost gelled; G = gelled; LVGS, MVGS, HVGS = low, medium and high viscosity gel slurries, respectively; NG = not gelled; all samples through 20 mesh unless otherwise speci-fied.
(b) Acrylamide-sodium acrylate ~30:70 wt. %) copolymer crosslinked with 0.5% MBA based on nomer weight.
(c) Epichlorohydrin crosslinked carboxymethyl cellulose (XL CMC) having 0.7 D.S. ( _759~ through 60 mesh) 10 (d) 50:50 wt. % blend of Example l-A and fine-cut chemical cotton (e) 50:50 wt. % blend of Example l-A and XL CMC.
Table 2 CAP Test Data on Crosslinked Cellulose-Svnthetic Polymer Products Absorption Per Time Interval*
Sample 1 3 5 10 15 20 25 30 35 40 45 Example 12 0.40.60.71.01.11.3 1.4 1.5 1.6 1.7 1.8 Fibrous Chemi- 0.81.92.83.74.34.5 4.5 4.5 cal Cotton (FCC) FCC coated with 0.92.33.55.46.16.4 6.5 6.5 6.5 2596 Of Example 12 by weight Example 13 1.11.92.53.74.65.4 6.1 6.6 7.0 7.5 7.7 Example 14 2.04.05.26.46.56.5 6.5 Staple Cotton 0.40.60.81.11.41.6 1.8 2.0 2.1 2.2 2.3 Example 18 1.02.33.45.77.58.2 8.6 8.8 8.9 9.0 9.0 *Absorption of 1% NaCl solution ~ml./g. of sample) at vario~s times in minutes ExamDle 22 Using the procedure substantially as described in Example l-A, 30 a fibrous chemical cotton was reacted in 570 ml. of toluene and 200 ml. of acetone with a 50/50 by weight mixture of acrylamide and sodium acrylate. The cataIyst additions comprised 0.1 g. aliquot of potassium persulfate and 0.4 g. aliquots of activator. The yield of product was quantitative; vinyl polymer content - 6196.
The product of this reaction was ground in a Wiley intermedi-ate mil7 to 20 mesh particle size. Analysis of the ground material showed a nitrogen content of 6.3596 indicating that the acrylamide to sodium acrylate ratio in the product was 45:55. The product compared favorably with Example 1-B in the water absorption capacity 40 and was slightly slower in rate of water absorption at liquid to solid ratios of 50:1 and 25:1. It was inferior to Example 1-~ in ~075233 rate of absorption of 1~ sodium chloride solution at liquid to solid ratios of 25:1 and 20:1.
Example 23 One gram of the material from Example l-B as it came from the reactor in pellet form and one gram of the same material after be-ing ground through 20 mesh were slurried in 500 ml. portions of distilled water. After standing for 48 hours at room temperature, the gels were collected on tared fluted filter papers. After draining over a wee~end in a closed system, the amount of water 10 drained from the ground sample was 248 g. and from the unground sample 255 g.
The gel from the 20-mesh material was dried in a forced draft oven at 105C. for 4 hours followed by 18 hours at 100C. in a con-vection oven. The weight of product recovered was 0.95 g. indica-ting only 5~ loss from extraction and handling.
The gel from the unground material was washed three times with acetone, then dried four hours at 60C. in vacuo followed by 18 hours at 100C. in a convection oven. The weight of product recovered was one gram, indicating no loss from extraction and 20 handling.
ExamPle 24 Two one-gram lots of the product of Example 5 (dry basis), ground through 20 mesh, were slurried in 500 ml. of distilled water. After standing 24 hours at room temperature, the slightly viscous supernatant liquid was separated from the insoluble material by careful decantation. The water-insoluble material was slurried in 500 ml. of acetone and left standing at room tempera-ture over a weekend. The difficultly filterahle supernatant liquid was filtered through tared fluted filter papers in a closed system 30 over a period of seven days. The amount of liquid drained throu~h the filters in this time was 440 ml. in one case and 445 ml. in the other. The filter papers were dried 18 hours at 100C. in a con-vection oven and found to have lost 0.06 g. in weight in each case, indicating that substantially no water-insoluble material was ~(~75f~3;~
present in the supernatant liquid passed through the filter papers.
Excess acetone was removed from the above acetone slurries ofthe water-insoluble material and the solids washed twice more with acetone to remove water. After removal of excess acetone, the solids were dried in vacuo at 60C. followed by la hours at 100C.
in a convection oven. The weight of recovered water-insoluble material was 0.38 g. in each case, indicating a 62% loss from ex-traction and handling.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of preparing a modified polysaccharide which exhibits high absorbency for water and salt solutions, which method comprises reacting a water-insoluble, water-swellable polysaccharide simultaneously with acrylamide or methacrylamide, at least one other water-soluble monoolefinic vinyl monomer which, in the absence of the polysaccharide, is copolymerizable with acrylamide or methacrylamide to form a water-soluble copolymer, and a water-soluble co-polymer, and a water-soluble free radical polymerizable divinyl monomer, in the presence of a free radical catalyst system, said reaction being carried out in a reaction medium comprising a substantially water-immiscible inert liquid diluent having dispersed therein water equal to about 1.5 to 2.5 times the weight of the aforesaid reactants and a low boiling, water-miscible, or-ganic liquid which has a low chain transfer constant, in an amount equal to about 25 to 65% of the volume of the aromatic hydrocarbon.
2. The method according to claim 1 wherein the substantially water-immiscible inert liquid is an aromatic hydrocarbon.
3. The method according to claim 1 or 2 wherein the low boiling, water-miscible organic liquid which has a low chain transfer constant is acetone or isopropanol.
4. The method according to claim 1 wherein the polysaccharide material is selected from the class consisting of cellulose, oxidized cellulose, starch and guar gum.
5. The method according to claim 1 wherein the water-immiscible inert liquid is toluene and the low boiling, water-miscible organic liquid is ace-tone.
6. The method according to claim 5 wherein the polysaccharide material is selected from the class consisting of cellulose, oxidized cellulose, starch and guar gum.
7. The method according to claim 6 wherein the other vinyl monomer is sodium acrylate and the divinyl monomer is methylene-bis-acrylamide.
8. The method according to claim 7 wherein the acrylamide component of the vinyl monomers is about 20 to 30% by weight thereof.
9. The method according to claim 5 wherein the amount of acetone is between about 30 and 55% based on the volume of toluene.
10. A method of preparing a water-insoluble cellulose derivative having high absorbency for water and salt solutions which comprises reacting cel lose or oxidized cellulose simultaneously with acrylamide, sodium acrylate and methylene-bis-acrylamide in the presence of a free radical catalyst sy-stem, said reaction being carried out in a reaction medium comprised of tol-uene, water equal to 1.5 to 2.5 times the combined weight of the reactants, and acetone in an amount equal to about 30 to 55% of the volume of the toluene.
11. A modified polysaccharide which exhibits high absorbency for water and salt solutions and which is obtained by reacting a water-insoluble, water-swellable polysaccharide simultaneously with acrylamide or methacrylamide, at least one other water-soluble monoolefinic vinyl monomer which, in the absence of the polysaccharide, is copolymerizable with acrylamide or methacrylamide to form a water-soluble copolymer, and a water-soluble copolymer, and a water-soluble free radical polymerizable divinyl monomer, in the presxence of a free radical catalyst system, said reaction being carried out in a reaction medium comprising a substantially water-immiscible inert liquid diluent having dis-persed therein water equal to about 1.5 to 2.5 times the weight of the afore-said reactants and a low boiling, water-miscible, organic liquid which has a low chain transfer constant, in an amount equal to about 25 to 65% of the volume of the aromatic hydrocarbon.
12. A modified polysaccharide according to claim 11 wherein the water-insoluble, water-swellable polysaccharide comprises about 10 to 60% by weight of the total mass of the modified polysaccharide.
13. A modified polysaccharide according to claim 11 wherein the water-insoluble, water-swellable polysaccharide is cellulose and the other water-soluble vinyl monomer is sodium acrylate.
14. A modified polysaccharide according to claim 11, 12 or 13 wherein the acrylamide content of the synthetic polymer is about 20 to 30%.
15. A modified polysaccharide according to claim 11, 12 or 13 wherein the acrylamide content of the synthetic polymer is about 20 to 30% and the synthetic polymer is crosslinked by methylene-bis-acrylamide.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/625,332 US4028290A (en) | 1975-10-23 | 1975-10-23 | Highly absorbent modified polysaccharides |
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| CA1075233A true CA1075233A (en) | 1980-04-08 |
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| US (1) | US4028290A (en) |
| JP (1) | JPS6021164B2 (en) |
| AU (1) | AU507842B2 (en) |
| BE (1) | BE846610A (en) |
| BR (1) | BR7607083A (en) |
| CA (1) | CA1075233A (en) |
| DE (1) | DE2647420C2 (en) |
| ES (1) | ES451462A1 (en) |
| FR (1) | FR2328719A1 (en) |
| GB (1) | GB1535574A (en) |
| IT (1) | IT1069013B (en) |
| MX (1) | MX144321A (en) |
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Families Citing this family (90)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4200557A (en) * | 1973-12-07 | 1980-04-29 | Personal Products Company | Absorbent product including grafted insolubilized cellulose ether |
| US4134863A (en) * | 1976-12-06 | 1979-01-16 | The United States Of America As Represented By The Secretary Of Agriculture | Highly absorbent graft copolymers of polyhydroxy polymers, acrylonitrile, and acrylic comonomers |
| US4194998A (en) * | 1976-12-06 | 1980-03-25 | The United States Of America As Represented By The Secretary Of Agriculture | Highly absorbent polyhydroxy polymer graft copolymers without saponification |
| GB1594389A (en) * | 1977-06-03 | 1981-07-30 | Max Planck Gesellschaft | Dressing material for wounds |
| US4242242A (en) * | 1977-06-10 | 1980-12-30 | Akzona Incorporated | Highly absorbent fibers of rayon with sulfonic acid polymer incorporated |
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|---|---|---|---|---|
| US2922768A (en) * | 1956-04-12 | 1960-01-26 | Mino Guido | Process for polymerization of a vinylidene monomer in the presence of a ceric salt and an organic reducing agent |
| US3065041A (en) * | 1958-04-23 | 1962-11-20 | American Cyanamid Co | Method of graft-polymerizing acrylate monomers onto paper in presence of ethylene dimethacrylate, and resulting product |
| NL275109A (en) * | 1961-02-28 | |||
| US3184421A (en) * | 1961-05-24 | 1965-05-18 | Eastman Kodak Co | Polymeric composition prepared from cellulose sulfate and alkyl acrylate and textilematerial coated therewith |
| US3297786A (en) * | 1961-10-03 | 1967-01-10 | Yardney International Corp | Method of graft polymerizing onto hydrophobic substrates |
| US3455853A (en) * | 1964-03-09 | 1969-07-15 | Union Oil Co | Method for preparing polysaccharide graft copolymers |
| NL125103C (en) * | 1965-08-20 | |||
| US3809664A (en) * | 1973-08-16 | 1974-05-07 | Us Agriculture | Method of preparing starch graft polymers |
-
1975
- 1975-10-23 US US05/625,332 patent/US4028290A/en not_active Expired - Lifetime
-
1976
- 1976-07-22 CA CA257,545A patent/CA1075233A/en not_active Expired
- 1976-09-11 ES ES451462A patent/ES451462A1/en not_active Expired
- 1976-09-21 FR FR7628254A patent/FR2328719A1/en active Granted
- 1976-09-24 BE BE170963A patent/BE846610A/en not_active IP Right Cessation
- 1976-09-27 JP JP51115731A patent/JPS6021164B2/en not_active Expired
- 1976-09-30 MX MX166507A patent/MX144321A/en unknown
- 1976-10-20 DE DE2647420A patent/DE2647420C2/en not_active Expired
- 1976-10-21 NL NLAANVRAGE7611635,A patent/NL174149C/en not_active IP Right Cessation
- 1976-10-22 SE SE7611761A patent/SE433222B/en unknown
- 1976-10-22 AU AU18909/76A patent/AU507842B2/en not_active Expired
- 1976-10-22 IT IT28629/76A patent/IT1069013B/en active
- 1976-10-23 BR BR7607083A patent/BR7607083A/en unknown
- 1976-10-25 GB GB44238/76A patent/GB1535574A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2647420C2 (en) | 1982-12-02 |
| JPS5251482A (en) | 1977-04-25 |
| NL174149C (en) | 1984-05-01 |
| IT1069013B (en) | 1985-03-21 |
| JPS6021164B2 (en) | 1985-05-25 |
| NL174149B (en) | 1983-12-01 |
| FR2328719A1 (en) | 1977-05-20 |
| AU507842B2 (en) | 1980-02-28 |
| SE7611761L (en) | 1977-04-24 |
| US4028290A (en) | 1977-06-07 |
| ES451462A1 (en) | 1977-12-16 |
| FR2328719B1 (en) | 1980-10-31 |
| DE2647420A1 (en) | 1977-04-28 |
| BR7607083A (en) | 1977-09-06 |
| MX144321A (en) | 1981-09-29 |
| AU1890976A (en) | 1978-04-27 |
| SE433222B (en) | 1984-05-14 |
| NL7611635A (en) | 1977-04-26 |
| GB1535574A (en) | 1978-12-13 |
| BE846610A (en) | 1977-01-17 |
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