JPH05123573A - Preparation of highly water absorptive cellulose material - Google Patents

Abstract

PURPOSE:To prepare a highly water absorptive cellulose material which has high water absorptive function for not only water but also an aqueous solution such as salts, urine, etc., containing ions. CONSTITUTION:A crosslinked cellulose derivative is swelled in a mixed treatment solution consisting of water, an organic solvent compatible with water, and an ammonium salt or an alkali metal salt to give a gel having 3-50g/g swelling degree and the obtained gel is separated from the treatment solution by filtration, and then, after the gel is washed by an organic solvent compatible with water or immersed in the organic solvent to replace the water in the gel with the organic solvent, it is dried to give the objective highly water absorptive cellulose material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superabsorbent cellulose material, and more particularly to a method for producing a superabsorbent cellulose derivative material having an excellent salt water absorbing ability. The highly water-absorbent material obtained in the present invention not only absorbs a large amount of water, but also exhibits a high water-absorbing ability with respect to an aqueous solution containing ions such as saline and urine. It is useful in a wide range of fields such as sanitary materials, agricultural materials, food packaging materials, and civil engineering / construction materials.

[0002]

2. Description of the Related Art As a water absorbing material for water or an aqueous solution containing salts such as saline, a group of resin materials called super absorbent resins have been developed and put into practical use in recent years. Basically, these resin materials have a chemical structure in which a water-soluble polymer is slightly cross-linked and is insolubilized in water. Examples of such a highly water-absorbent material include, for example, starch obtained by graft-polymerizing acrylonitrile and then hydrolyzing it, starch obtained by graft-polymerizing acrylic acid metal salt, and acrylic acid polymerized with a copolymerizable cross-linking agent. A large number of crosslinking resins, hydrolysates of methyl methacrylate-vinyl acetate copolymers, etc. have been proposed, and some of them have been put into practical use.

Cotton, pulp, paper, cloth, sponge, etc., which are known as traditional water-absorbing materials, absorb water by a capillary phenomenon, whereas the above-mentioned superabsorbent resin has a principle of absorbing water. Because of its osmotic pressure, it can absorb much more water than capillarity. Further, the highly water-absorbent resin has an excellent feature that it does not easily re-emit water even when pressure is applied in a water-absorbing state. For this reason, the applications of super absorbent polymers are as follows: disposable paper diapers, sanitary materials such as sanitary products, soil water retention agents, agricultural material fields such as nursery sheets, food fields such as food freshness-retaining materials, dehydration materials, and tunnel excavation. It is widely used as a civil engineering / building material such as a sheet for preventing sludge loss and a sheet for preventing condensation on buildings.

However, when these super absorbent polymers are applied to a solution containing salt such as saline or urine, the osmotic pressure, which is the driving force of water absorption, is decreased by the presence of the salt, and the water absorption amount is remarkably reduced. It has the drawback of Further, even in the field of application of the above super absorbent polymer, since a solution containing a salt is often targeted, development of a material exhibiting a high water absorption amount even in the presence of the salt is desired.

In order to solve the above-mentioned drawbacks of conventional super absorbent polymers, unlike the synthetic polymers such as sodium polyacrylate described above, the polysaccharides are not thread-like in salt water and have spread relatively. Attempts have been made to utilize polysaccharides by paying attention to the property of retaining a conformation. For example, a method in which a hydrophilic monomer is graft-polymerized to a polysaccharide (JP-A-56-76419, JP-A-56-76419).
76481), a method of cross-linking the polysaccharide itself (JP-A-56-5137, JP-A-58-79006, JP-A-60-58443) and the like. Further, a method using a cellulose derivative (in particular, carboxymethyl cellulose is often used) as the polysaccharide (Japanese Patent Laid-Open No. Sho 49-49).
-128987, JP-A-50-85689, JP-A-54-163981, JP-A-56-28755, JP-A-58-1701, JP-A-60-94401, and JP-A-61-89364. No.) is also under consideration. However, it cannot be said that the salt water absorption capacity was sufficiently improved by either method.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a method capable of easily and inexpensively producing a cellulose derivative material having a high water absorption even in an aqueous solution containing various salts. ..

[0007]

That is, a method for producing a superabsorbent cellulose material according to the present invention comprises a crosslinked cellulose derivative, water, an organic solvent compatible with water, an ammonium salt and an alkali metal. In the mixed treatment liquid with at least one selected from salt, the swelling degree is 3
g / g to 50 g / g to swell, then the mixed solution is filtered to separate the crosslinked cellulose derivative gel from the mixed solution, and the water content in the gel is an organic solvent compatible with water. It is characterized in that it is dried after being replaced with.

[0008]

The cellulose derivative used in the present invention includes carboxymethyl cellulose (hereinafter abbreviated as CMC) alkali metal salt, carboxymethyl hydroxyethyl cellulose alkali metal salt, carboxyethyl cellulose alkali metal salt, cellulose sulfate alkali metal salt and the like. An electrolyte-based water-soluble cellulose derivative is used. There is no particular limitation on the crosslinking method for such a cellulose derivative, but a method of crosslinking by heating (thermal crosslinking), a method of reacting a crosslinking agent, and the like can be used.

Examples of the cross-linking agent used for cellulose derivatives include formaldehyde and aldehydes such as glyoxal, N-methylol compounds such as dimethylolurea, dimethylolethyleneurea, and dimethylolimidazolidone, oxalic acid, and maleic acid. , Succinic acid, and polyvalent carboxylic acids such as polyacrylic acid, polyhydric epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and diepoxy butane, divinyl sulfone, and divinyl compounds such as methylenebisacrylamide , Polychlorohalogen compounds such as dichloroacetone, dichloropropanol, and dichloroacetic acid,
Halohydrin compounds such as epichlorohydrin and epibromohydrin as well as polyvalent aziridine compounds can be used.

The cross-linked cellulose derivative used in the method of the present invention is produced by graft-copolymerizing a water-soluble monomer with a raw material cellulose derivative, and further subjecting this to hydrolysis and cross-linking. The water absorbent crosslinked cellulose derivative material may be used. As the raw material cellulose derivative in this case, non-electrolyte-based cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and acetyl cellulose can be used in addition to the above water-soluble cellulose derivatives.

As the water-soluble monomer which is graft-copolymerized with the raw material cellulose derivative, acrylic acid, methacrylic acid,
And monomers having a carboxyl group such as alkali metal salts thereof, and carboxyl groups by hydrolysis such as acrylamide, methacrylamide, acrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. Monomers having groups that generate groups can be used.

The cross-linking treatment applied to the graft copolymer is
It may be before or after graft polymerization, or may be crosslinked by the same method as in the case of the electrolyte-based water-soluble cellulose derivative, or divinyl copolymerizable with the above-mentioned monomer in the course of graft copolymerization. Compounds such as N,
The graft copolymerization may be carried out in the presence of N'-methylenebisacrylamide, N, N'-methylenebismethacrylamide, ethylene glycol diacrylate and the like.

The shape of the crosslinked cellulose derivative may be any of fibrous, powdery, particulate, sheet-like, and the like, but there is no particular limitation, but when fibrous ones are used, the water absorption rate is excellent. There is an advantage that a fibrous superabsorbent material can be obtained.

The organic solvent used in the method of the present invention is not particularly limited as long as it is compatible with water, and these can be used. Examples of useful organic solvents include methanol, ethanol, n
-Propanol, isopropanol, n-butanol,
There are isobutanol, t-butanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile and the like, and one kind or a mixture of two or more kinds thereof can be used.

Ammonium salt used in the method of the present invention,
As the alkali metal salt, any water-soluble one can be used. Examples of these salts are ammonium chloride, lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, ammonium sulfate, lithium sulfate, sodium sulfate, potassium sulfate, ammonium nitrate, sodium nitrate, potassium nitrate, ammonium phosphate, sodium phosphate, Potassium phosphate, ammonium carbonate, ammonium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, ammonium sulfite, sodium sulfite, potassium sulfite, ammonium formate, sodium formate, potassium formate, ammonium acetate, sodium acetate, potassium acetate , Ammonium acrylate, sodium acrylate, potassium acrylate and the like, and at least one of them can be used. Among these salts, the ammonium salt is preferable because it has high solubility not only in water but also in the above-mentioned organic solvent, so that the amount remaining in the superabsorbent material obtained by the method of the present invention is small.

The swelling treatment step for the crosslinked cellulose derivative is carried out by adding a mixed treatment liquid of water, the above organic solvent and the above salt thereto. At this time, it may be heated or may not be heated, but it is necessary to control the swelling degree of the crosslinked cellulose derivative to 3 g / g to 50 g / g.

Here, the "swelling degree" is the gram amount of the mixed solvent held by 1 g of the material to be swollen, and is specifically measured by the method described later. The degree of swelling varies depending on various factors, but the main factors are the mixing ratio of water, an organic solvent and a salt, the addition amount of the mixed solution, and the crosslink density of the cellulose derivative. By appropriately adjusting these factors, a gel having the above swelling degree can be prepared.

When the degree of swelling is less than 3 g / g, the effect of the method of the present invention is hardly recognized, and it is 50 g.
When it is higher than / g, the gel becomes too soft and it is difficult to separate the gel from the mixed solution by filtration.

The crosslinked cellulose derivative does not swell in the above organic solvent containing no water. However, when water is mixed with the above organic solvent to reduce the concentration of the organic solvent, it has a property of rapidly swelling at a certain concentration. This phenomenon is well known as “volume phase transition of gel”. In the method of the present invention, since it is a necessary condition to swell the crosslinked cellulose derivative, the mixing ratio of the organic solvent and water is set to an organic solvent concentration causing this volume phase transition, or an organic solvent concentration slightly lower than that. To set. The suitable concentration of the organic solvent varies depending on the type of the crosslinked cellulose derivative and the type of the organic solvent and cannot be specified unconditionally, but is generally 15 to 65% by weight.

If the concentration of the organic solvent in the mixed solution is too high, the swelling of the crosslinked cellulose derivative hardly occurs as described above, and therefore it cannot be used. On the other hand, when it is too low, the gel remarkably swells and becomes soft, and it becomes difficult to separate the gel by filtration, which is not preferable.

The salt used in the method of the present invention is selected from alkali metal salts and ammonium salts as described above, and these are salts which form a monovalent cation. Since a salt forming a divalent or higher cation such as a heavy metal salt or an alkaline earth metal salt forms an ionic cross-link with respect to a cross-linked cellulose derivative, the water absorption amount of the resulting water-absorbing material is reduced, and thus Cannot be used for methods.

The mixing ratio of the salt to the mixture of the organic solvent and water is also a property that cannot be specified unconditionally, but generally 0.2% by weight to 5% by weight of the mixture of the water and the organic solvent.
It may be mixed by weight%. When the mixing ratio of the salt is high, the swelling degree of the gel is suppressed, which is advantageous for separating the gel from the mixed solution by filtration, but when the mixing ratio of the salt is too high, the amount of the salt remaining in the filtered gel is increased. May increase the water content of the gel and hinder the water absorption performance of the gel, resulting in inconvenience such as extra cost for its removal. Also it is 0.2% by weight
If the amount is less than that, there is almost no effect of mixing the salt, which may cause inconvenience such as excessive swelling degree of the gel.

The addition amount of the mixed treatment liquid of water, organic solvent and salt should also be changed depending on the type of crosslinked cellulose derivative, the type of organic solvent, the concentration of organic solvent, the type of salt and the crosslinking density. But generally 20-200
It may be added at a rate of kg / kg. If the addition amount is too small, the swelling of the gel will be incomplete and a superabsorbent material cannot be obtained, and if it is too high, the amount of the organic solvent used will increase and the cost will increase, which is not preferable. ..

The crosslink density of the crosslinked cellulose derivative used as a starting material in the method of the present invention is adjusted so that the above swelling degree is achieved when the mixing ratio of water, the organic solvent and the salt and the addition amount thereof are adjusted. Good.

Filtration of the swollen gel separates most of the solvent and salts. This operation is effective in reducing the heat energy required for removing and drying salts harmful to the water absorption performance of the gel.

Since the filtered gel still contains water, when it is heated and dried as it is, the gel particles adhere to each other due to water to form a hard resinous substance, which does not exhibit a high water absorption amount. Therefore, the water in the gel can be replaced with the organic solvent by washing the gel with the above organic solvent that is compatible with water, or by immersing the gel in this organic solvent and then filtering this. Then, this is dried to obtain a superabsorbent cellulose material.

As to the cellulose derivative-based water-absorbing material, many studies have been made and reported as exemplified above. However, in the value of water absorption of pure water or artificial urine, the cross-linked polyacrylic acid is used. No significant value has been reported as compared with the sodium-based super absorbent polymer. However, many water-soluble cellulose derivatives retain a high viscosity even in salt water, and thus are considered to be potentially capable of exhibiting a high salt water absorption ability.

The reason why an excellent superabsorbent material can be obtained by the method of the present invention has not been clarified yet, but the most important point is that a crosslinked cellulose derivative is
It is considered to be to swell once. One of the effects obtained by swelling in this way is the reduction of water-soluble components in the gel. The crosslinked cellulose derivative used in the method of the present invention is synthesized by crosslinking a water-soluble cellulose derivative as described above.
In this case, it is inevitable that part of the water-soluble cellulose derivative remains in the gel as a water-soluble component without being cross-linked. When a large amount of this water-soluble component is present in the gel, when the gel is swollen, the gel particles stick to each other and cause lumps and the like, which is not preferable as a practical product. In particular, as in the case of the object of the present invention, in order to obtain a material exhibiting a high water absorption amount, it is necessary to theoretically reduce the crosslink density. Volume also tends to increase.
In order to remove such a water-soluble component, a method of washing the crosslinked cellulose derivative with water may be considered, but in the case of a cellulose derivative having a low crosslink density, it absorbs a very large amount of water and swells. Therefore, the drying requires a huge amount of heat energy, which is not realistic. Therefore, the method using water washing can be applied only to a cellulose derivative having a high crosslinking density and therefore a small water absorption amount. Instead of water, a method of suppressing swelling by using a mixture of water and an organic solvent compatible with water, and a method of suppressing swelling by using a mixture of water and a salt are also conceivable. As described above, in a mixture of water and an organic solvent, a phenomenon called volume phase transition occurs, and the swelling occurs discontinuously, so that the degree of swelling cannot be controlled arbitrarily. In the latter case, swelling cannot be effectively suppressed unless a large amount of salt is mixed, and thus a large amount of salt remains in the gel, which is not preferable.

However, an organic solvent compatible with water is mixed with water so that the crosslinked cellulose derivative has a concentration causing a volume phase transition or a concentration slightly lower than that, and further the above salt is added. When mixed with, in the mixed treatment liquid, it becomes possible to effectively suppress the swelling at a low salt concentration even with a cellulose derivative having a low crosslinking density,
And it has been found that the degree of swelling can be changed continuously by changing the mixing ratio of water, organic solvent and salt. Therefore, according to the method of the present invention, the water-soluble component in the gel can be effectively removed at a low cost.

The reason why a water absorbing material having a high water absorption amount can be obtained by the method of the present invention cannot be sufficiently explained only by removing the above water-soluble components. That is, the water absorbing material obtained by the method of the present invention exhibits a water absorption much higher than the water absorption estimated from the removal of the water-soluble component. It is presumed that this effect is because the intermolecular hydrogen bond developed in the cellulose derivative by swelling is broken, the network structure is deformed, and water is easily taken in between the molecular networks. By washing the gel in this state with an organic solvent that is compatible with water, or by immersing the gel in this organic solvent, the water content in the gel can be replaced with the organic solvent, and when this is dried, It is considered that the network structure formed by swelling is preserved as it is, and thereby a high water absorption amount is developed. When dried without replacement with an organic solvent, hydrogen bonds are reformed due to the influence of water content in the gel, which not only reduces the effect of deforming the network structure but also makes the resulting water-absorbing material a solid resinous material. As a result, high water absorption performance cannot be obtained.

[0031]

The present invention will be further described with reference to the following examples.
Of course, the scope of the invention is not limited by these examples. The water absorption in the examples and comparative examples was measured by the following method.

(1) Method for measuring water absorption of artificial urine solution 1 g of the test material was enclosed in a bag made of 250 mesh nylon wire and having a length and width of 10 cm. It was soaked for a minute to absorb water.
This was lifted and suspended, drained for 10 minutes, then weighed, and the amount of water absorbed was indicated by the weight of the artificial urine absorbed per 1 g of the sample.

(2) Swelling degree measuring method 0.5 g of the test material was placed in a beaker, and a mixed treatment liquid consisting of water, an organic solvent compatible with water, and a salt was added in accordance with a desired swelling condition. The test material was swollen and gelled. This gel is enclosed in a bag made of 250 mesh nylon wire and having a length and width of 10 cm, suspended and drained for 10 minutes, then sandwiched between 10 upper and lower filter papers and placed on a horizontal press table. Place it on it and have a diameter 1
A stainless plate having a size of 6 cm and a weight of 100 g was stacked, and a weight of 1 kg was further placed on the stainless plate to apply pressure to the gel for 5 minutes, so that the liquid existing in the gap between the gel and the filter paper was sucked up. Then, the weight of the gel was measured, and the swelling degree of the gel was indicated by the weight of the mixed treatment liquid absorbed per 1 g of the sample.

Example 1 Softwood kraft pulp (NBKP) having an absolute dry weight of 20 g was disintegrated with a household mixer to obtain a cotton-like material. This cotton-like material was placed in a reaction vessel, and 312 g of isopropanol, 40 g of water, and 5.93 g of sodium hydroxide were mixed and stirred for 1 hour to prepare alkali cellulose. To this, 17.3 g of sodium monochloroacetate was added, stirred for 30 minutes, and allowed to stand for another 30 minutes. Next, a reflux condenser was attached to the reaction vessel, and the mixed liquid was heated under reflux in an oil bath for 3 hours. The reaction product is filtered through a glass filter,
After thoroughly washing with wt% methanol, washing twice with 100% methanol and drying in a vacuum drier, 30 g of fibrous CMC sodium salt (degree of substitution 1.0) was obtained.

30 g of this fibrous CMC sodium salt was placed in a reaction vessel, and 600 ml of isopropanol, 120 ml of water, and 18 ml of an isopropanol solution containing epichlorohydrin at a concentration of 50 g / l, and a concentration of 40 g were added.
9.7 ml of an aqueous solution containing 1 / l NaOH were mixed. Attach a reflux condenser to the reaction vessel, and put the mixed solution in an oil bath.
Heated to reflux for hours. The reaction product mixture was filtered through a glass filter and thoroughly washed with 70% by weight of methanol, and then 100
% Methanol and then dried in a vacuum drier to obtain a fibrous cross-linked CMC.

100 ml of water and 100 ml of methanol were put into a 300 ml beaker and mixed to prepare 179 g of a 44% by weight methanol aqueous solution. Ammonium chloride 4 was added to this aqueous methanol solution to adjust the salt concentration to 2.2% by weight.
g was dissolved.

3 g of the above-mentioned cross-linked CMC was added to this mixed treatment liquid, and after stirring, the cross-linked CMC was swollen by leaving it at room temperature for 1 hour. The swelling degree of the crosslinked CMC under this swelling condition was measured and found to be 8 g / g. The mixture was filtered to separate the gel, which was dispersed in 60 ml of 76% by weight methanol, 60 ml of methanol was added thereto, and the mixture was allowed to stand for 1 hour to replace most of the water in the gel with methanol. Further, this mixed solution is filtered to separate the gel, and the separated gel is dispersed in 60 ml of methanol and allowed to stand for 6 hours to sufficiently replace water in the gel with methanol, and then the gel is filtered and dried. Thus, a fibrous super absorbent material was obtained.
The water absorption of the artificial fluid was measured, and the results are shown in Table 1.

Example 2 In a 300 ml beaker, 120 ml of water and 8 parts of isopropanol
0 ml was added and mixed to prepare 182 g of an isopropanol aqueous solution having a concentration of 34% by weight. 3 g of sodium chloride was dissolved in this so that the salt concentration was 1.6% by weight. To this mixed solution, 3 g of crosslinked CMC obtained by the same method as in Example 1 was added, stirred, and then allowed to stand at room temperature for 1 hour to swell. The degree of swelling of the crosslinked CMC under this swelling condition was measured and found to be 10 g / g. The mixture was filtered to separate the gel, the gel was dispersed in 60 ml of 65% by weight isopropanol, 60 ml of isopropanol was added, and the mixture was allowed to stand for 1 hour to replace most of the water in the gel with isopropanol. .. The mixture was filtered to separate the gel, and the gel was dispersed in 60 ml of isopropanol and allowed to stand for 6 hours to sufficiently replace water in the gel with isopropanol, and then the gel was filtered and dried. A fibrous super absorbent material was obtained. The water absorption of the artificial urine is shown in Table 1.

Example 3 In a 300 ml beaker, 140 ml of water and 60 ml of acetone were put and mixed to prepare 187 g of an aqueous acetone solution having a concentration of 25% by weight. 5 g of anhydrous sodium sulfate was dissolved in this so that the salt concentration was 2.7% by weight. To this mixed solution, 3 g of crosslinked CMC obtained by the same method as in Example 1 was added, stirred, and then allowed to stand at room temperature for 1 hour to swell. The degree of swelling of the crosslinked CMC under this swelling condition was measured to be 22
It was g / g. The mixture is filtered to separate the gel,
This gel was dispersed in 120 ml of a 65 wt% acetone aqueous solution, 120 ml of acetone was added, and the mixture was allowed to stand for 1 hour.
Most of the water in the gel was replaced with acetone. Further, this mixed solution is filtered to separate the gel, the gel is dispersed in 60 ml of acetone and left standing for 3 hours to sufficiently replace the water in the gel with acetone, and then the gel is filtered and dried. ,
A fibrous super absorbent material was obtained. The water absorption of the artificial urine is shown in Table 1.

Example 4 Commercially available powdered CMC sodium salt (degree of substitution 0.8) 30
To g, 260 g of isopropanol, 78 g of water, 2 g of sodium hydroxide, and 22 g of ethylene oxide were mixed, and this mixture was charged into an autoclave and kept at 70 ° C. for 2 hours.
Reacted for hours. The resulting reaction mixture is then neutralized with acetic acid, filtered to remove most of the reaction solvent, and stored at 60 ° C. for 4 hours.
After drying for an hour, the temperature was further raised to 150 ° C., and the mixture was heated for 2 hours to prepare a crosslinked carboxymethylhydroxyethyl cellulose sodium salt.

In a 300 ml beaker, 60 ml of water and 40 ml of acetone were added and mixed to prepare 92 g of an acetone aqueous solution having a concentration of 34% by weight. 1 g of potassium chloride was dissolved in this so that the salt concentration was 1.1% by weight. 3 g of the crosslinked carboxymethyl hydroxyethyl cellulose sodium salt was added to this mixed solution, stirred, and then allowed to stand at room temperature for 30 minutes to swell. When the degree of swelling of the crosslinked carboxyhydroxyethyl cellulose sodium salt under this swelling condition was measured, it was 16 g / g. The mixture was filtered to separate the gel, the gel was dispersed in 60 ml of acetone, and then allowed to stand for 1 hour to replace most of the water in the gel with acetone. Further, this mixed solution was filtered to separate the gel, the gel was dispersed in 60 ml of acetone and left standing for 6 hours to sufficiently replace the water in the gel with acetone, and then the gel was filtered and dried. Then, it was lightly pulverized to obtain a powdery super absorbent material. The water absorption of the artificial urine is shown in Table 1.

Example 5 To a softwood kraft pulp (NBKP) having an absolute dry weight of 7 g,
154 g of 0.1% nitric acid and 14 g of acrylonitrile were added and mixed well. To this mixture was added 370 mg of ceric ammonium nitrate as a graft polymerization initiator, and graft polymerization was carried out at room temperature for 1 hour. The obtained reaction product is thoroughly washed with water, filtered, dehydrated, and then added with 1000 ml of a 3% aqueous sodium hydroxide solution and heated at 100 ° C. for 2 hours to hydrolyze the graft copolymerized pulp. gave. The reaction product obtained is separated by filtration,
After washing with a 6 wt% methanol aqueous solution, vacuum drying was performed to obtain a hydrolyzate of the graft copolymerized pulp.

Next, to 5 g of this hydrolyzate was added 50 ml of isopropanol, 10 ml of water, and 1.5 ml of sodium hydroxide.
g, and the mixture was stirred at room temperature for 1 hour, 4.4 g of sodium monochloroacetate was added thereto, and the mixture was further mixed with 4 g.
The hydrolysis product was subjected to carboxymethylation by heating at 0 ° C. for 3 hours, and the obtained reaction product was washed with 70% by weight of methanol and then dried in vacuum. A hydrolyzate of carboxymethylated graft copolymer pulp was obtained.

The hydrolyzate of the carboxymethylated graft copolymer pulp was subjected to the same operations as in Example 1 to obtain a fibrous superabsorbent material. However, the swelling degree when the hydrolyzate of the carboxymethylated graft copolymerized pulp was swollen was 6 g / g. Table 1 shows the artificial urine water absorption of this superabsorbent material.

Comparative Examples 1 to 3, Comparative Examples 1 and 4 and 5, respectively, are the samples before swelling with a mixture of water, an organic solvent compatible with water, and a salt. The products of Comparative Examples 2 and 3 were used. Table 1 shows the amounts of water absorbed by these artificial urine solutions.

Comparative Example 4 In Comparative Example 4, the same operation as in Example 1 was performed. However, as a solvent for swelling the cross-linked CMC, 70% by weight methanol 179 was used instead of the mixture in which 4 g of ammonium chloride was dissolved in 179 g of the 44% by weight methanol aqueous solution.
using a mixture of 4 g of ammonium chloride dissolved in
As shown in Table 1, the degree of swelling of the crosslinked CMC was kept low. Table 1 shows the artificial urine water absorption of the obtained product.

Comparative Example 5 In Comparative Example 5, the same operation as in Example 1 was performed. However, as a solvent for swelling the cross-linked CMC, 44% by weight methanol 179 was used instead of the mixture in which 4 g of ammonium chloride was dissolved in 179 g of the 44% by weight methanol aqueous solution.
A mixture in which 0.25 g of ammonium chloride was dissolved in g was used. However, the degree of swelling became too large, and the gel could not be separated by filtration, so that a superabsorbent material could not be obtained.

Comparative Example 6 In Comparative Example 6, the same operation as in Example 1 was performed. However, as a solvent for swelling the cross-linked CMC, 10% by weight methanol 179 was used instead of the mixture in which 4 g of ammonium chloride was dissolved in 179 g of the 44% by weight methanol aqueous solution.
When a mixture in which 4 g of ammonium chloride was dissolved in g was used, the degree of swelling became too large, the gel could not be separated by filtration, and a superabsorbent material could not be obtained.

Comparative Examples 7 to 11 In Comparative Examples 7 to 11, the same operations as in Examples 1 to 5 were performed. However, the samples prepared by drying in a drier at 105 ° C. without displacing the water content of the gel separated by swelling and then filtering were prepared as Comparative Example 7, Comparative Example 8, Comparative Example 9, and Comparative Example 10, respectively. did. Table 1 shows the artificial urine water absorption of these products.

[0050]

[Table 1]

[0051]

The highly water-absorbent material of the present invention obtained by the above method rapidly swells not only in pure water but also in salt water and exhibits a high water absorption, and can be suitably used in a wide variety of fields.

Claims (1)

[Claims] 1. A crosslinked cellulose derivative is added to water,
In a mixed treatment liquid of an organic solvent compatible with water, and at least one selected from an ammonium salt and an alkali metal salt, swelling so that the degree of swelling is 3 g / g to 50 g / g, Next, the mixed solution is filtered to separate the crosslinked cellulose derivative gel from the mixed solution, water in the gel is replaced with an organic solvent having compatibility with water, and then dried. A method for producing a highly water-absorbent cellulose material having excellent salt water absorption ability.