JPH0549925A - Production of highly water-absorbable cellulose material - Google Patents

Abstract

PURPOSE:To produce a highly water-soluble cellulose material showing high water absorbing capacity not only to water but also to an aqueous solution containing an ion such as a saline solution or urine. CONSTITUTION:A crosslinked cellulose derivative is swollen in water or a liquid mixture of water and an org. solvent compatible with water to form a gel with a swelling degree of 20-200g/g and an org. solvent compatible with water is added to said gel to deswell the gel. This gel is filtered to be separated from the solvent and washed with or immersed in the org. solvent compatible with water to substitute the moisture in the gel with the org. solvent and, thereafter, the gel is dried to obtain the objective highly water-absorbable 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 highly water-absorbent cellulose material, and more particularly to a method for producing a highly water-absorbent 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 In recent years, a group of polymeric resin materials called super absorbent resins have been known and put into practical use as water absorbent materials for water or aqueous solutions containing salts such as saline. Basically, these resin materials have a chemical structure in which a water-soluble polymer is slightly crosslinked to make it insoluble 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 to 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 include disposable paper diapers, sanitary materials such as sanitary products, soil water retention agents, agricultural materials such as nursery sheets, food freshness retention materials, dehydration materials, etc. 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, these highly water-absorbent resins have a drawback that the water absorption amount is remarkably reduced because the osmotic pressure, which is the driving force of water absorption, is reduced in a solution containing salt such as saline solution or urine. There is. In the field of application of the above super absorbent polymer, a solution containing a salt is often targeted. Therefore, it is desired to develop a material exhibiting a high water absorption amount even in the presence of the salt.

In order to solve the above-mentioned drawbacks of conventional superabsorbent resins, unlike synthetic polymers such as sodium polyacrylate, the polysaccharide does not become a thread-like molecule even in salt water, and it is a comparatively wide-ranging polymer. Attempts have been made to take advantage of the property of retaining formation. For example, a method in which a hydrophilic monomer is graft-polymerized onto a polysaccharide (Japanese Patent Laid-Open No. S60-12065).
56-76419, JP-A-56-76481), a method of crosslinking the polysaccharide itself (JP-A-56-5137, JP-A-58-79006, JP-A-60-58443) and the like. ing. In addition, a method using a cellulose derivative (in particular, carboxymethyl cellulose is often used) as the polysaccharide (Japanese Patent Laid-Open No. 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) have also been studied. However, it cannot be said that the salt water absorption capacity was sufficiently improved by either method.

[0006]

SUMMARY 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, the method for producing a superabsorbent cellulose material of the present invention is to swell a crosslinked cellulose derivative in a mixed solution of water and an organic solvent compatible with water. The gel has a degree of 20 g / g to 200 g / g, to which an organic solvent compatible with water is added,
The gel is de-swelled, the resulting mixture is filtered to separate the crosslinked cellulose derivative gel from the solvent, and the water in the gel is replaced with an organic solvent compatible with water, and then dried. It is a feature.

[0008]

The cellulose derivative used in the present invention is an electrolyte type such as carboxymethyl cellulose (hereinafter abbreviated as CMC) alkali metal salt, carboxymethyl hydroxyethyl cellulose alkali metal salt, carboxyethyl cellulose alkali metal salt, and cellulose sulfate alkali metal salt. A water-soluble cellulose derivative or the like is used.
The method for crosslinking the cellulose derivative is not particularly limited, but a method of crosslinking by heating (thermal crosslinking), a method of reacting a crosslinking agent, and the like can be used.

As cross-linking agents, aldehydes such as formaldehyde and glyoxal; N-methylol compounds such as dimethylolurea, dimethylolethyleneurea, and dimethylolimidazolidone; oxalic acid, maleic acid, succinic acid, and polyacrylic acid. Polycarboxylic acids such as acids; polyepoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and diepoxy butane; divinyl sulfone, and divinyl compounds such as methylenebisacrylamide, dichloroacetone, dichloropropanol , And polyvalent halogen compounds such as dichloroacetic acid; halohydrin compounds such as epichlorohydrin and epibromohydrin; and polyvalent aziridine compounds Kill.

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

As the water-soluble monomer, acrylic acid,
Monomers having carboxyl groups such as methacrylic acid and alkali metal salts thereof, acrylamide, methacrylamide, acrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, etc. Monomers containing groups that give rise to groups can be used.

The cross-linking treatment may be carried out before or after the graft polymerization, or may be carried out by the same method as in the case of the electrolyte-based water-soluble cellulose derivative. The graft copolymerization may be carried out in the presence of a divinyl compound copolymerizable with the monomer, for example, N, N'-methylenebisacrylamide, N, N'-methylenebismethacrylamide, ethylene glycol diacrylate and the like.

The crosslinked cellulose derivative may be in the form of fiber, powder, particles, sheet or the like without any particular limitation. However, if a fibrous material is used, a fibrous highly water-absorbing material having an excellent water absorption rate can be obtained.

The organic solvent compatible with water used in the method of the present invention is at least one selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile and the like. You can

In the method of the present invention, the swelling of the crosslinked cellulose derivative is carried out by adding a mixture of water and an organic solvent compatible with water. At this time, it is necessary to make the degree of swelling of the crosslinked cellulose derivative 20 to 200 g / g.

Here, the "swelling degree" is the weight of the mixed solvent held by the material to be swollen, and is specifically measured by the method described later. The degree of swelling is determined by various factors, and the main factors are the mixing ratio of water and the organic solvent, the addition amount, and the crosslinking density. By appropriately adjusting these factors, a gel having the above-mentioned degree of swelling can be obtained.

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 the "volume phase transition of gel",
In the swelling step of the method of the present invention, it is preferable to use an organic solvent concentration that causes this volume phase transition or an organic solvent concentration that is slightly lower than that. 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 20 to 60% by weight.

When the concentration of the organic solvent is too high, the swelling degree of the crosslinked cellulose derivative is lowered as described above, which is not preferable. On the other hand, if it is too low, the amount of the organic solvent required for de-swelling described below increases, which is not preferable because the production cost significantly increases, and the water-absorbing material obtained becomes a resinous material. This causes the disadvantage that the water absorption speed becomes slow.

The addition amount of the mixed solvent should be changed depending on the type of crosslinked cellulose derivative, the type of organic solvent, the concentration of organic solvent, and the crosslink density, but generally 20 to 20% relative to the crosslinked cellulose derivative. 400 kg / k
It may be added in a ratio of g. If the amount added is too small, the degree of swelling of the gel will be too small to obtain a superabsorbent material, and if it is too high, the cost of the organic solvent 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 may be adjusted so that the swelling degree becomes the above when the mixing ratio of water and the organic solvent and the addition amount thereof are adjusted.

The swollen gel is de-swelled by adding the solvent compatible with water, and most of the solvent retained by the gel is released. Next, this mixed solution is filtered to separate the crosslinked cellulose derivative gel from the solvent. The type of solvent used for the deswelling may be the same as or different from the organic solvent used for the swelling. This deswelling operation also has the effect of reducing the thermal energy required to dry the gel, but its main purpose is to remove most of the water from the gel prior to drying. If this operation is not performed and the swollen gel is heated and dried as it is, gel particles adhere to each other due to the action of water to form a hard resinous material, and the dried cellulose material does not exhibit a high water absorption amount.

Since the filtered gel still contains some water, it is washed with the above-mentioned organic solvent compatible with water or soaked in water, and then filtered to remove water in the gel. Can be replaced with an organic solvent,
This can be 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, cross-linked sodium polyacrylate is used. No value is reported that is much higher than that of the super absorbent polymer. However, since many water-soluble cellulose derivatives retain high viscosity even in salt water, they are potentially materials capable of exhibiting high salt water absorption ability.

The reason why an excellent superabsorbent material can be obtained by the method of the present invention is not clear yet, but
It can be considered as follows. That is, the most important point is to swell the crosslinked cellulose derivative in a mixture of water and an organic solvent compatible with water, which causes breakage of intermolecular hydrogen bonds, etc. The structure is irreversibly deformed, and a gel structure that easily absorbs water is formed between molecular networks. Deswelling this with an organic solvent compatible with water, further replacing the water remaining in the gel with an organic solvent and drying, the network structure formed by the swelling is preserved, high water absorption It is considered to occur. Therefore, unless the swelling degree of the gel is set to 20 g / g or more in the swelling step, it is considered that the deformation of the network structure is not sufficient and a high water absorption amount cannot be obtained. When swelling is performed only with water, de-swelling is likely to be incomplete, hydrogen bonds are reformed due to the influence of residual moisture, and the effect of deforming the network structure is reduced, and the resulting water-absorbing material is Since it becomes a resinous material, high water absorption performance cannot be obtained.

This phenomenon is considered to be a phenomenon peculiar to the cellulose derivative system in which an interaction system between molecules by hydrogen bonding has been developed. For example, in the case of a crosslinked poly (sodium acrylate) -based highly water-absorbent resin, the interaction between molecules due to hydrogen bonds is small, and therefore the water absorption performance does not change at all even when treated by the method of the present invention.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to these examples. The water absorption amount and swelling degree in Examples and Comparative Examples were measured by the methods described below.

(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 of 10 cm square and immersed in artificial urine of the following composition for 10 minutes. It was made to absorb liquid. This was lifted and suspended, drained for 10 minutes, then weighed, and the weight of the artificial urine absorbed per 1 g of the sample was used to indicate the water absorption of the sample material. Artificial urine composition Ingredient Weight% Urea 2.00 NaCl 0.80 MgSO4 · 7H2O 0.08 CaCl2 · 2H2O 0.03 Pure water 97.09

(2) Method of measuring degree of swelling 0.5 g of the test material was placed in a beaker, and a mixed solution of water and an organic solvent compatible with water was added according to the swelling condition to swell the test material. Gelled. This gel was enclosed in a bag made of 250-mesh nylon wire of 10 cm square, suspended, drained for 10 minutes, the weight was measured, and the swelling degree was indicated by the weight of the mixed solution 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 and 40 g of water were added thereto.
g and 5.93 g of sodium hydroxide were mixed and stirred for 1 hour to obtain alkali cellulose. To this, 17.3 g of sodium monochloroacetate was added, stirred for 30 minutes,
It was left for another 30 minutes. Next, attach a reflux condenser to the reaction vessel, put the mixed solution in it, and put this in an oil bath.
Heated to reflux for hours. The reaction product was filtered through a glass filter, sufficiently washed with 70% by weight methanol aqueous solution, and then 10
Wash twice with 0% methanol, dry in a vacuum oven,
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 was added thereto.
120 ml of water, 18 ml of isopropanol solution containing epichlorohydrin with a concentration of 50 g / l, and concentration of 40 g
9.7 ml of an aqueous solution containing 1 / l NaOH were mixed. A reflux condenser was attached to the reaction vessel, and the mixture was heated under reflux on an oil bath for 1 hour. The reaction product mixture was filtered through a glass filter, thoroughly washed with 70% by weight aqueous methanol solution, washed twice with 100% methanol, and dried in a vacuum drier to obtain a fibrous crosslinked CMC.

500 ml of this fibrous cross-linked CMC 3 g
In a beaker, 200 g of 55% by weight methanol aqueous solution
Was added and stirred, and then the mixture was allowed to stand for 1 hour to swell the crosslinked CMC. The degree of swelling of the crosslinked CMC under this swelling condition was measured and found to be 50 g / g. After 200 g of acetone was added to the gel to deswell the gel, the gel was separated by filtration. This gel was dispersed in 100 g of acetone and left at room temperature for 6 hours to replace water in the gel with acetone, and then the gel was filtered and dried to obtain a fibrous superabsorbent material. The water absorption of the artificial urine was measured, and the results are shown in Table 1.

Example 2 3 g of fibrous crosslinked CMC obtained by the same method as in Example 1
Was placed in a 500 ml beaker, 200 g of a 25 wt% isopropanol aqueous solution was added, and after stirring, the mixture was left to stand for 1 hour to swell. Cross-linked CMC under this swelling condition
The swelling degree was measured to find that it was 63 g / g. After 200 g of isopropanol was added to this gel to swell the gel, the gel was separated by filtration. This gel was dispersed in 100 g of isopropanol and allowed to stand at room temperature for 6 hours to replace water in the gel with isopropanol.
The gel was filtered and dried to obtain a fibrous super absorbent material. The water absorption of the artificial urine is shown in Table 1.

Example 3 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 was 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.

3 g of this cross-linked sodium carboxymethyl hydroxyethyl cellulose salt was placed in a 500 ml beaker, and 400 wt.
After adding g and stirring, the mixture was left still for 1 hour and swollen. The swelling degree of the crosslinked sodium carboxymethylhydroxyethyl cellulose salt under the swelling condition was measured and found to be 110 g / g. After 400 g of acetone was added to the gel to deswell the gel, the gel was separated by filtration. This gel was dispersed in 100 g of acetone and left at room temperature for 6 hours to replace water in the gel with acetone. Next, the gel was filtered, dried, and then pulverized to obtain a super absorbent material. The water absorption of the artificial urine is shown in Table 1.

Example 4 0.1% was added to a softwood kraft pulp (NBKP) having an absolute dry weight of 7 g.
% 154 g of nitric acid and 14 g of acrylonitrile were added and mixed well. To this 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. Wash the reaction product thoroughly with water,
After filtering and dehydration, 3% aqueous sodium hydroxide solution 1000
By adding ml and heating at 100 ° C. for 2 hours,
The graft copolymerized pulp was hydrolyzed. The reaction product was separated by filtration, washed with a 76 wt% methanol aqueous solution, and then vacuum dried to obtain a hydrolysis product of the graft copolymerized pulp.

Next, 50 ml of isopropanol, 10 ml of water, and 1.5 g of sodium hydroxide were added to 5 g of this hydrolysis product, and the mixture was stirred at room temperature for 1 hour. Then, 4.4 g of sodium monochloroacetate was added, and this mixture was further mixed. The solution was heated at 40 ° C. for 3 hours to subject the hydrolysis product to carboxymethylation, washed with a 70% by weight aqueous methanol solution, and then dried under vacuum. A hydrolysis product of carboxymethylated graft copolymerized pulp was obtained. The carboxymethylated graft copolymerized pulp hydrolysis product was subjected to the same operations as in Example 1 to obtain a fibrous superabsorbent material. However, the degree of swelling when the hydrolysis product of the carboxymethylated graft copolymer pulp was swollen was 65 g / g. Table 1 shows the artificial urine water absorption of this superabsorbent material.

Comparative Examples 1 to 3 The same operations as in Example 1, Example 3 and Example 4 were performed, except that the samples before swelling with water and a mixture of water and an organic solvent compatible with each other were used. These are Comparative Example 1, Comparative Example 2 and Comparative Example 3. Table 1 shows the amounts of water absorbed by these artificial urine solutions.

Comparative Examples 4 to 7 In Comparative Examples 4 to 7, the same operations as in Examples 1 to 4 were performed. However, the addition amount of the mixture of water and the organic solvent was reduced to 30 g, and the degree of swelling was suppressed. Table 1 shows the artificial urine water absorption of each product.

Comparative Example 8 In Comparative Example 8, the same operation as in Example 1 was performed. However, as a solvent for swelling the crosslinked CMC, a 65% by weight aqueous methanol solution was used instead of the 55% by weight aqueous methanol solution, whereby the degree of swelling of the crosslinked CMC was suppressed to a low level. Table 1 shows the artificial urine water absorption of the obtained product.

Comparative Example 9 In Comparative Example 9, the same operation as in Example 2 was performed. However, as a solvent for swelling the cross-linked CMC, a 65 wt% isopropanol aqueous solution was used in place of the 25 wt% isopropanol aqueous solution, and the swelling degree was suppressed to a low level. The water absorption of the artificial urine is shown in Table 1.

Comparative Example 10 In Comparative Example 10, the same operation as in Example 3 was performed. However, as a solvent for swelling the crosslinked sodium carboxymethylhydroxyethyl cellulose salt, a 65 wt% acetone aqueous solution was used in place of the 35 wt% acetone aqueous solution to suppress the degree of swelling. The water absorption of the artificial urine is shown in Table 1.

Comparative Example 11 In Comparative Example 11, the same operation as in Example 4 was performed. However, as a solvent for swelling the hydrolyzate of the carboxymethylated graft copolymerized pulp, a 65 wt% methanol aqueous solution was used instead of the 55 wt% methanol aqueous solution to suppress the degree of swelling to a low level. The water absorption of the artificial urine is shown in Table 1.

Comparative Examples 12 to 15 In Comparative Examples 12 to 15, the same operations as in Examples 1 to 4 were performed. However, in Examples 1 to 4, the swollen gel was directly dried in a dryer at 105 ° C. to prepare the gel. The water absorption of the artificial urine is shown in Table 1.

Comparative Examples 16 and 17 In Comparative Example 16, 75 g of acrylic acid was placed in the reaction vessel.
To this, 201 g of water and 31.2 g of sodium hydroxide were added to neutralize 74.9% of the carboxyl groups of acrylic acid. Next, to this mixture, 0.05 g of N, N'-methylenebisacrylamide as a crosslinking agent and 0.26 g of potassium persulfate as a polymerization initiator were added and dissolved.

In a separate flask was placed 375 g of cyclohexane, and 4.5 g of sorbitan monostearate was dissolved as a surfactant in the flask. Then, the partially neutralized acrylic acid aqueous solution was added, and nitrogen gas was blown into the flask. The mixture was stirred to form a water-in-oil suspension. Then, the mixture was heated to 65 ° C. and polymerized. After cooling, the polymer particles obtained are separated by decantation,
It was dried in a vacuum dryer at 0 ° C. to obtain a crosslinked sodium polyacrylate-based highly water-absorbent resin (Comparative Example 16). The water absorption of the artificial urine is shown in Table 1.

In Comparative Example 17, 3 g of the crosslinked sodium polyacrylate-based super absorbent polymer was placed in a 500 ml beaker, 200 g of a 35 wt% methanol aqueous solution was added, and the mixture was stirred and allowed to swell by allowing the mixture to stand for 1 hour. The degree of swelling of the crosslinked sodium polyacrylate-based super absorbent polymer under this swelling condition was measured and found to be 66 g / g. After 200 g of acetone was added to the gel to deswell the gel, the gel was separated by filtration. This gel was dispersed in 100 g of acetone and left at room temperature for 6 hours to replace water in the gel with acetone, and then the gel was filtered and dried (Comparative Example 17). The water absorption of the artificial urine is shown in Table 1.

[0047]

[Table 1]

[0048]

The superabsorbent material obtained by the method of the present invention quickly swells not only in pure water but also in salt water and exhibits a high water absorption amount, so that it can be suitably used in a wide variety of fields.

Claims (1)

[Claims] 1. A crosslinked cellulose derivative is swollen in a mixed solution of water and an organic solvent compatible with water to give a gel having a degree of swelling of 20 g / g to 200 g / g. A compatible organic solvent is added to de-swell the gel, the resulting mixed solution is filtered to separate the crosslinked cellulose derivative gel from the solvent, and water in the gel is mixed with an organic solvent compatible with water. The method for producing a highly water-absorbent cellulose material having an excellent salt water-absorption capacity, the method comprising: