JPH0841103A - Production of water-absorbent cellulosic material - Google Patents

Abstract

PURPOSE:To easily and economically produce a cellilosic material which exhibits a high water absorption rate even for an aqueous solution containting various salts and comprises a cellulose derivative excellent in gel strength. CONSTITUTION:A crosslinked cellulose derivative which is water-insoluble because of crosslinkage and of which all the carboxyl groups are in acid form is dispersed in water, and an alkali is added to the dispersion to partially neutralize the carboxyl groups to convert into salt form, thus a cellulose derivative gel having a swelling degree of 3-30g/g is produced. After separation from water, the gel is mixed with an alkali in an organic solvent compatible with water to convert the remaining acid-from carboxyl groups into salt form. After the gel is separated from the solvent, the water in the gel is removed by replacement with an organic solvent and the gel is dried.

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 water-absorbent cellulose material having excellent salt water absorption capacity and gel strength. The water-absorbing 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 materials, agricultural materials, food packaging materials, and civil engineering / construction materials.

[0002]

2. Description of the Related Art In recent years, a group of materials called superabsorbent resins have been known as water-absorbing materials for water or aqueous solutions containing salts such as saline and have been put to practical use. 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 an 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 superabsorbent resin has the principle of absorbing water. Because it is osmotic, 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 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 dew condensation on buildings.

However, when these superabsorbent resins are used for a solution containing a salt such as saline or urine, the osmotic pressure, which is the driving force of water absorption, decreases, so that the amount of water absorption remarkably decreases. At the same time, it has a drawback that the mechanical strength of the gel is lowered. However, in the field of application of the above-mentioned superabsorbent resin, 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. Further, in the sanitary field such as disposable diapers and sanitary products, it is required to have an ability to absorb salt water under pressure, so that improvement in gel strength is also required.

In order to solve the above-mentioned drawbacks of conventional superabsorbent polymers, unlike synthetic polymers such as sodium polyacrylate, the molecules do not form a string in salt water, and a relatively wide conformation is formed. Attempts have been made to utilize polysaccharides that can be retained. For example, a method of graft-polymerizing a hydrophilic monomer onto a polysaccharide (Japanese Patent Laid-Open No. 56-7641).
No. 9, JP-A-56-76481, and a method for crosslinking the polysaccharide itself (JP-A-56-5137).
JP-A-58-79006, JP-A-60-5844
No. 3) and the like are known. Further, a method using a cellulose derivative (in particular, carboxymethyl cellulose is often used) as the polysaccharide (Japanese Patent Laid-Open No. 49-12898).
7, JP-A-50-85689, JP-A-54
-163981, JP-A-56-28755, JP-A-58-1701, JP-A-60-944
No. 01, No. 61-89364, No. 5
No. 80482) is also under consideration. However, it cannot be said that the drawbacks of the highly water-absorbent resin have been sufficiently improved by any of the methods.

On the other hand, the inventors of the present invention have prepared a water-insolubilized cellulose derivative in a mixed solution of water and an organic solvent.
Swelling to a degree of swelling of 3 to 30 g / g to form a gel of the cellulose derivative, separating from the solvent, and removing water in the gel by replacing it with an organic solvent having compatibility with water, Proposed is a method for producing a highly water-absorbent cellulose material having excellent water-absorbing ability of salt water by maintaining the carbon number and the content rate of the organic solvent within a specific range, which is composed of drying (JP-A-6-172401). Gazette). However, although a cellulose material excellent in salt water absorption can be obtained by this method, it has a drawback that it cannot be used as a sanitary material such as a disposable diaper or a sanitary product because it has a poor gel strength and loses its shape.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive investigations by the present inventors, in order to solve the drawbacks of the prior art, a method for producing a cellulose material which is excellent in both the water absorption capacity of an aqueous salt solution and the gel strength. , Water-insolubilized by cross-linking, and all of the carboxyl groups in water are acid type cellulose derivatives, by partially neutralizing the acid type carboxyl groups with an alkali to form a salt form, When swollen in a proportion, the cellulose derivative can be swollen uniformly and continuously,
As a result, they have found that a cellulose derivative having excellent properties of both water absorption capacity and gel strength can be obtained, and have completed the present invention.

An object of the present invention is to provide a method for easily and inexpensively producing a water-absorbent cellulose material composed of a cellulose derivative having a high water absorption amount even in an aqueous solution containing various salts and having an excellent gel strength. To do.

[0009]

According to the present invention, a cellulose derivative, which is water-insolubilized by cross-linking and has all carboxyl groups in acid form, is dispersed in an aqueous medium, and then alkali is added to remove the carboxyl groups. Soothing degree of swelling is 3 ~ 30g /
g of a cellulose derivative gel, which is then separated from water and placed in an organic solvent that is compatible with water,
The acid type carboxyl group remaining in the gel is returned to the salt type by adding an alkali, and after further separating the gel from the solvent, the water in the gel is replaced by the organic solvent to remove it. A method for producing a water-absorbing cellulose material having excellent salt water-absorbing ability and gel strength, which is characterized by drying.

[0010]

The cellulose derivative which is water-insolubilized by the cross-linking and has all the carboxyl groups in the acid form used in the present invention is a water-soluble cellulose derivative having a carboxyl group such as carboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose and carboxyethyl cellulose. As a raw material, there is a raw material in which one or more kinds are appropriately selected from these and are used for crosslinking, and all of the carboxyl groups are in an acid form. There is no particular limitation on the method of crosslinking the water-soluble cellulose derivative,
A method of crosslinking by heating (thermal crosslinking) or a method of chemically reacting a crosslinking agent can be used.

As the crosslinking agent in this case, aldehydes such as formaldehyde and glyoxal; N-methylol compounds such as dimethylolurea, dimethylolethyleneurea and dimethylolimidazolidone; oxalic acid,
Polyvalent carboxylic acids such as maleic acid, succinic acid, polyacrylic acid; ethylene glycol diglycidyl ether,
Polyvalent epoxy compounds such as polyethylene glycol diglycidyl ether and diepoxy butane; Divinyl compounds such as divinyl sulfone and methylene bisacrylamide; Polyvalent halogen compounds such as dichloroacetone, dichloropropanol and dichloroacetic acid;
Halohydrin compounds such as epichlorohydrin and epibromohydrin; and polyvalent aziridine compounds can be used.

As another method for producing a cellulose derivative which is used in the method of the present invention and which is insolubilized in water by a cross-linking and whose carboxyl groups are all in the acid form, a specific monomer is added to cellulose or a cellulose derivative. May be graft-copolymerized, and if necessary, hydrolyzed and cross-linked as described above, and all the carboxyl groups may be acid-type. In addition to the above water-soluble cellulose derivatives, non-electrolyte-based cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, acetyl cellulose can be used as the raw material cellulose derivative in this case.

The monomer used in the graft copolymerization is a monomer having a carboxyl group such as acrylic acid, methacrylic acid and alkali metal salts thereof,
Monomers containing a group that produces a carboxyl group by hydrolysis such as acrylamide, methacrylamide, acrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and the like 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, or further in the course of the graft copolymerization. Graft copolymerization may be carried out in the presence of a divinyl compound copolymerizable with the monomer, such as N, N-methylenebisacrylamide, N, N'-methylenebismethacrylamide, or ethylene glycol diacrylate.

The cellulose derivative as the exemplified raw material is generally produced in a salt type state in which an alkali metal ion is bound to a carboxyl group. In the present invention, first,
The alkali metal ion is removed to make the carboxyl group into an acid state. For that purpose, the simplest method is to immerse the raw material cellulose derivative in an aqueous solution of a strong acid to keep the pH at 1 or less.

The strong acid used for converting the carboxyl group of the cellulose derivative into an acid form may be any acid capable of lowering the pH to 1 or less, such as hydrochloric acid, nitric acid, bromic acid, iodic acid, sulfuric acid, perchloric acid, Examples thereof include inorganic compounds such as phosphoric acid and organic compounds such as aspartic acid, citric acid, glutamic acid, oxalic acid, salicylic acid, malonic acid, phosphinic acid and phosphonic acid. However, hydrochloric acid or sulfuric acid is most suitable in consideration of manufacturing cost and ease of handling. The acid concentration of the strong acid aqueous solution is 0.5 to 4 N, though it varies depending on the type of acid or cellulose derivative. When the concentration is low, the acid form is not completely formed, and when the concentration is too high, the raw material cellulose derivative itself is hydrolyzed, and it becomes difficult to remove excess acid, which is not preferable.

The amount of the strong acid aqueous solution added is determined in relation to the type and concentration of the acid, but the pH of the solution during the treatment must be kept at 1 or less at all times.
10 to 150 kg may be added per unit. If the addition amount is small, the acid form is not completely formed, and if the addition amount is too large, the use amount of the acid increases, which is not preferable. The time for immersion in a strong acid aqueous solution also varies depending on the acid concentration and the type of cellulose derivative,
Minutes to 2 hours. This time may be a time required for all the carboxyl groups of the cellulose derivative to be in the acid form, but a longer time tends to improve the gel strength of the superabsorbent cellulose derivative obtained. Note that this reaction is 5 to 30 considering the case of using a volatile strong acid.
It is preferable to carry out at room temperature of ° C. The raw material cellulose derivative treated by the above method is separated from the aqueous acid solution by filtration, centrifugal dehydration, etc., and then washed with water to remove excess acid attached to obtain a cellulose derivative in which all carboxyl groups are in the acid form. Can be done.

Then, the acid-type cellulose derivative thus obtained is dispersed in water and alkali is added,
The cellulose derivative is swollen to form a gel by neutralizing the cellulose derivative so that the swelling degree becomes 3 to 30 g / g and converting a part of the acid-type carboxyl group into a salt type. Here, the “swelling degree” is the weight of water 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 factor is the rate of conversion of acid-type carboxyl groups to salt-type.
The crosslinked cellulose derivative does not swell in water when all the carboxyl groups are in the acid form, but when it is converted into the salt form, the swelling degree changes depending on the conversion ratio. The conversion ratio of the carboxyl group from the acid type to the salt type for obtaining the swelling degree varies depending on the type of the cellulose derivative and the crosslinking density, but is in the range of 20 to 70% of the total carboxyl groups.

By appropriately adjusting the above-mentioned factors, the cellulose derivative can be made into a gel having the swelling degree. If the degree of swelling is less than 3 g / g, the desired performance cannot be obtained in terms of water absorption and gel strength. Conversely, if the degree of swelling is 30 g / g or more, the gel becomes too soft and the gel is filtered from an aqueous medium and centrifuged. It is not suitable because it becomes difficult to separate it by dehydration.

Examples of the alkali used for neutralization by adding to the cellulose derivative having an acid type carboxyl group include sodium hydroxide, lithium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide. However, sodium hydroxide is preferred. The amount of water added to disperse the cellulose derivative having an acid-type carboxyl group should be changed depending on the type of the cellulose derivative and the crosslink density, but is in the range of 50 to 100 kg per 1 kg of the absolutely dried cellulose derivative. . If the amount added is less than 50 kg, the swelling of the gel will be uneven and a highly water-absorbing material cannot be obtained.
Also, if it exceeds 100 kg, it becomes difficult to separate water from the gel, which is not suitable.

Subsequently, the produced gel is filtered, and the obtained gel is dispersed in an organic solvent which is compatible with water, and an alkali is added while suppressing swelling, and the remaining acid-type carboxyl is added. The group is returned to the salt form. The amount of the organic solvent added at this time is 20 to 30 kg per 1 kg of the gelled absolutely dried cellulose derivative, although it depends on the type of gel and the degree of swelling. If the amount added is small, the salt form will not be uniform, and if the amount added is too large, the amount of the organic solvent used will increase, resulting in waste. The filtration is performed by using a known filter cloth, a filtration device using a wire net, and a centrifugal dehydrator,
It is performed by selecting the mesh of the filter medium according to the gel condition. The organic solvent is preferably one that dissolves alkali as much as possible, and monohydric alcohols such as methanol and ethanol and glycerin are suitable. Above all, methanol is most suitable for obtaining a fibrous superabsorbent cellulose material.

Since the gel of the cellulose derivative converted to the salt form contains water, if it is dried as it is, the particles of the gel adhere to each other by the water to form a hard resinous material. This one does not show high water absorption and cannot be used as it is, thus requiring extra cost for grinding and dispersion. Therefore, the gel in the salt form is filtered to separate the gel from the solvent, and again immersed in an organic solvent that is compatible with water, and then filtered to replace the water remaining in the gel with the organic solvent. Therefore, the water-absorbent cellulose material can be obtained by heating and drying the thus-treated gel of the cellulose derivative. The shape of the water-absorbent cellulose material in the present invention is not particularly limited such as fibrous, powdery, particulate and sheet-like, but the fibrous material is excellent in water absorption rate.

The reason why an excellent superabsorbent material can be obtained by the method of the present invention is not yet fully clarified, but it is thought that the most important point is to swell the crosslinked cellulose derivative. One of the effects obtained by swelling is the reduction of water-soluble components in the gel. The crosslinked cellulose derivative used in the present invention is synthesized by crosslinking a water-soluble polymer as described above. In this case, it is unavoidable that a part of the water-soluble polymer remains in the gel as a water-soluble component without being cross-linked. If a large amount of this water-soluble component is present in the gel, it may cause stickiness, residue, etc. when the gel is swollen, leading to a decrease in water absorption capacity and gel strength.

Therefore, it is necessary to theoretically increase the crosslink density and remove the water-soluble component. For this purpose, a method of washing the crosslinked cellulose derivative with water can be considered. In this case, the above-mentioned cellulose derivative is used. Since it absorbs a very large amount of water and swells, it requires an enormous amount of heat energy for drying, which is not realistic. Therefore, a method of suppressing the swelling of the cellulose derivative and swelling it uniformly to remove the water-soluble component is required. As such a method, instead of water, a mixture of an organic solvent compatible with water is used. A method of suppressing swelling by using a mixture of water and a salt is also considered. However, the former usually
Since it swells discontinuously due to the phenomenon of volume phase transition, the degree of swelling cannot be controlled arbitrarily, and in the latter case, swelling cannot be effectively suppressed unless a large amount of salt is mixed, and in the gel. It is not preferable because a large amount of salt remains.

On the other hand, as in the present invention, a cellulose derivative which is insoluble in water by cross-linking and has a carboxyl group of all acid type is dispersed in water, and alkali is added to this to partially neutralize the carboxyl group. When the degree of swelling is adjusted so that the degree of swelling is 3 to 30 g / g by blending into a salt form, discontinuous swelling due to volume phase transition is significantly suppressed, and the acid form of the carboxyl group is converted into a salt form. By changing the rate of conversion to the mold, it is possible to change to nearly continuous swelling.

On the other hand, the reason why a water absorbing material having a high water absorption amount can be obtained by the present invention cannot be explained only by the removal of the above water-soluble component, and in fact, the water absorption amount is much higher than that estimated from the removal of the water-soluble component. High water absorption is obtained. Such an effect is that the swelling partially breaks the intermolecular hydrogen bond or the breaking of the cross-linking point developed in the cellulose derivative, and the network structure is deformed so that water can be easily taken in between the network of molecules. Is presumed to be the cause.

Therefore, by washing the gel in this state with an organic solvent that is compatible with water or by immersing it in the organic solvent, the water in the gel can be replaced with the organic solvent and removed. , Whereby the gel can be dried easily. Moreover, in this case, since most of the network structure formed by swelling is preserved, it is considered that high water absorption is exhibited. If the gel is dried without removing the water in the gel with the organic solvent, hydrogen bonds are reformed due to the influence of water in the gel, and the effect of deforming the network structure is reduced, and it is obtained. High water absorption performance cannot be obtained because the water-absorbent material becomes a hard resinous material.

Further, the reason why a high gel strength is obtained is that the swelling of the cellulose derivative is carried out in water.
It is considered that the water-soluble components in the gel are completely removed, and that when the carboxyl group of the cellulose derivative is converted into an acid form, an ester bond is newly generated between the molecules to strengthen the crosslinking.

As described in detail above, according to the present invention, it is possible to obtain a highly water-absorbent cellulosic material in which both salt water absorption and gel strength are remarkably improved.

[0030]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In Examples and Comparative Examples,% means% by weight.

Example 1 20 g of an absolutely dry bleached softwood kraft pulp was disintegrated with a household mixer to give a cotton-like material. Put this cotton-like material in a reaction vessel and add 400 ml of isopropanol and 40 m of water.
1, and 6.20 g of sodium hydroxide were mixed and stirred for 1 hour to obtain alkali cellulose. 17.3 g of sodium monochloroacetate and 0.6 of epichlorohydrin
g was added, the mixture was stirred for 30 minutes, and left for another 30 minutes.
Then, a reflux condenser was attached to the reaction vessel, and the mixed solution was heated under reflux for 3 hours in an oil bath. The reaction product was filtered through a glass filter (2G), thoroughly washed with 70% methanol-water mixture, washed twice with 100% methanol, and dried in a vacuum dryer to obtain fibrous crosslinked carboxymethyl cellulose. Sodium salt 30 (hereinafter referred to as CMC)
g (degree of substitution 1.0) was obtained.

Cross-linked CM in a 500 ml beaker
Take 3 g of C sodium salt (absolutely dry) and use 1N hydrochloric acid 30
0 ml was added, the mixture was stirred for 30 minutes and left for 30 minutes. This mixture was filtered through a glass filter (2G) to separate crosslinked CMC having an acid type carboxyl group, and further, washing and filtration with pure water were repeated to remove excess acid. Cross-linked CM having this acid type carboxyl group
C is placed in a 300 ml beaker, 200 ml of pure water is added and dispersed, and 1N sodium hydroxide aqueous solution is 6.64 ml.
Was added and stirred to partially neutralize and swell to form a gel. In this swelling condition, the conversion rate to the salt type was 60%, and the swelling degree of the crosslinked CMC was 28 g.
/ G.

The mixture was filtered through a glass filter (2G) to separate the gel and transferred to a 200 ml beaker.
After adding 60 ml of 100% methanol to the gel to disperse it, 1N sodium hydroxide-methanol solution 3.1 was added.
The remaining acid type carboxyl group was returned to the salt type while adding 0 ml and stirring. After standing for 1 hour, the gel was filtered through a glass filter (2G), the filtered product was immersed in 100 ml of 100% methanol, and the water in the gel was replaced with methanol to remove it. After standing for 1 hour, the gel was filtered through a glass filter (2G), washed again with 100% methanol, and dried under reduced pressure at 50 ° C. for 3 hours to obtain a fibrous water-absorbent cellulose material.

Using the obtained water-absorbent cellulose material, the water absorption amount and gel strength of the artificial urine solution were tested by the test methods shown below, and the quality thereof was evaluated. Table 1 shows the results.

Test Method (1) Water Absorption of Artificial Urine Solution 0.8 g of absolutely dried test material was sealed in a 250-mesh nylon wire bag of 10 cm square and was placed in an artificial urine solution of the following composition. It was soaked in water for 10 minutes to absorb water. This was lifted and suspended, drained for 10 minutes, then weighed, and the water absorption (g / g) was shown by the weight of the artificial urine absorbed per 1 g of the sample dried. This water absorption is 4
If it is 0 g / g or more, it can be practically used. Artificial urine composition Ingredient% Urea 2.00 Sodium chloride 0.80 Magnesium sulfate 0.08 Calcium chloride 0.03 Pure water 97.09

(2) Gel Strength 1 g of absolutely dried sample material was placed in a 100 ml weighing bottle, and 20 ml of the above artificial urine solution was added to form a uniform gel. After standing for 2 hours, press the gel with your finger to set the hardness of the gel to the next 4
The grade was evaluated. The gel strength was rated as ◯ (hard) and ◎ (very hard). ◎: Very hard ○: Hard △: Soft ×: Very soft

(3) Swelling degree 1 g of absolutely dried sample material was gelled according to the examples and comparative examples of the present invention. That is, the crosslinked CMC having an acid type carboxyl group is placed in a 300 ml beaker and pure water 2
After being placed in 00 ml and dispersed, a predetermined aqueous sodium hydroxide solution was added and swollen with stirring to form a gel.
This gel was sealed in a 10-cm-square 250-mesh nylon wire bag, suspended, drained for 10 minutes, then placed in a bag and sandwiched between 10 upper and lower filter papers on a horizontal press table. Put it on top of it and have a diameter of 16 cm on it,
Stack 100g stainless steel plate and 1k on it
A weight of g was applied and pressure was applied to the gel for 5 minutes so that water existing in the gap between the gel and the gel was absorbed by the filter paper. Thereafter, the weight of the gel was measured, and the weight of water absorbed per 1 g of the sample dried was defined as the degree of swelling (g / g).

Example 2 3 g of crosslinked CMC sodium salt obtained in the same manner as in Example 1 was placed in a 500 ml beaker, 300 ml of 2N sulfuric acid was added, and the mixture was stirred for 30 minutes and then left for 30 minutes. This mixture was filtered to separate crosslinked CMC having an acid type carboxyl group, and further, washing and filtration were repeated with pure water to remove an excess acid. Take the acid-type cross-linked CMC in a 300 ml beaker and add pure water 2
After adding 00 ml and dispersing, 3.32 ml of 1N aqueous sodium hydroxide solution was added and partially neutralized and swollen with stirring to form a gel. The conversion rate to the salt form under this swelling condition was 30%, and the swelling degree of the crosslinked CMC sodium salt was 15 g / g.

The mixture was filtered as in Example 1 to separate the gel and transferred to a 200 ml beaker. After 60 ml of ethanol was added to the gel to disperse it, 5.43 ml of 1N sodium hydroxide-ethanol solution was added and the residual carboxyl group of acid form was returned to the salt form with stirring. After standing for 1 hour, the gel was filtered and 100 ml of 100% ethanol was added to replace the water in the gel to remove it.
The gel was filtered after standing for 1 hour, washed again with 100% ethanol and then dried to obtain a fibrous water-absorbing material. The artificial urine water absorption and gel strength of this material were measured, and the results are shown in Table 1.

Example 3 2.0 g of a crosslinking agent (trade name: SUMITEX, NF-500K, manufactured by Sumitomo Chemical Co., Ltd.), an auxiliary agent (trade name: SUMITE)
X, Accelerator, MX, manufactured by Sumitomo Chemical Co., Ltd.) 1.
0 g and 297.0 g of water are mixed to make 300 g of a mixed solution, and 20 g of absolutely dried coniferous bleached kraft pulp is mixed therein.
Soak for 0 minutes. The mixed liquid in the pulp is 24 in terms of solid content.
The excess mixture was removed by filtration and pressing so that g was included. The obtained sheet-shaped pulp was sufficiently dried at room temperature, and then heated in a blow dryer at 140 ° C. for 30 minutes to crosslink. The crosslinked pulp was disintegrated with a household mixer to give a cotton-like material. This cotton-like material was placed in a reaction vessel and 400 ml of isopropanol, 40 ml of water,
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, 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 was filtered through a glass filter (2G), thoroughly washed with 70% methanol, then washed twice with 100% methanol, and then dried in a vacuum dryer to obtain 30 g of fibrous crosslinked CMC sodium salt. (Substitution degree 1.0) was obtained.

Cross-linked CM in a 500 ml beaker
Take 3 g of C sodium salt and add 1.5N hydrochloric acid to 300
After adding ml, the mixture was stirred for 30 minutes and left for 30 minutes. This mixture was filtered to separate acid type cross-linked CMC, and washing and filtration were repeated with pure water to remove excess acid. The cross-linked CMC having a carboxyl group of this acid type is 3
In a 00 ml beaker, 200 ml of pure water was added and dispersed, and 6.64 ml of a 1N aqueous sodium hydroxide solution was added, and partially neutralized and swollen with stirring to form a gel. The conversion rate to the salt form under this swelling condition was 60%, and the swelling degree of the crosslinked CMC was 28 g / g. The mixture is filtered to separate the gel, 200
Transferred to a ml beaker. After 60 ml of 100% methanol was added to the gel to disperse it, 3.10 ml of 1N sodium hydroxide-methanol solution was added and the remaining carboxyl groups of the acid form were returned to the salt form with stirring. After standing for 1 hour, the gel was filtered, 100 ml of 100% methanol was added to replace the water in the gel, and the gel was removed. After standing for 1 hour, the gel was filtered, washed again with 100% methanol and then dried to obtain a fibrous water-absorbing material. Using this material, the artificial urine water absorption and gel strength were measured, and the results are shown in Table 1.

Example 4 Commercially available powdery CMC sodium salt (degree of substitution: 0.65,
Viscosity of 1% aqueous solution: 280 cps, product name: Serogen W
S-C, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) 30 g of isopropanol 3
33 ml, 78 ml of water, 2 g of sodium hydroxide, and 22 g of ethylene oxide were charged into an autoclave, and this mixture was reacted at 70 ° C. for 2 hours. Next, the reaction mixture was neutralized with acetic acid, filtered to remove most of the reaction solvent, and dried at 60 ° C. for 4 hours to prepare hydroxyethylcarboxymethylcellulose sodium salt (hereinafter referred to as HECMC sodium salt). 30 g of this HECMC sodium salt was placed in a reaction vessel, and 600 ml of isopropanol, 120 ml of water, and 4.5 g of ethylene glycol diglycidyl ether were mixed therein. A reflux condenser was attached to the reaction vessel, and the mixture was refluxed and heated in an oil bath for 2 hours to carry out a crosslinking reaction. The reaction mixture was filtered through a glass filter (2G), thoroughly washed with 70% methanol, washed twice with 100% methanol, and dried in a vacuum dryer to obtain a crosslinked HECMC sodium salt.

Crosslinked HE in a 1 liter beaker
Take 3 g of CMC sodium salt and add 0.7N hydrochloric acid 45
0 ml was added, the mixture was stirred for 30 minutes, and left for 90 minutes. This mixture was filtered to separate crosslinked HECMC having an acid type carboxyl group, and further, washing with pure water and filtration were repeated to remove excess acid. Take this acid-type cross-linked HECMC in a 300 ml beaker and add pure water 30
After 0 ml was added and dispersed, 3.32 ml of a 1N aqueous sodium hydroxide solution was added, and the mixture was partially neutralized and swollen with stirring to form a gel. The conversion rate to the salt form under this swelling condition was 30%, and the swelling degree of the crosslinked HECMC was measured and found to be 25 g / g. The mixture was filtered to separate the gel and transferred to a 200 ml beaker. To this gel, 60 ml of 100% methanol was added and dispersed, and 1N sodium hydroxide-methanol solution 5.4 was added.
The remaining acid type carboxyl groups were returned to the salt type while adding 3 ml and stirring. After standing for 1 hour, the gel is filtered,
100 ml of 100% methanol was added to replace water in the gel to remove it. After standing for 1 hour, the gel was filtered, washed again with 100% methanol and then dried to obtain a powdery water-absorbing material. Using this material, the artificial urine water absorption and gel strength were measured, and the results are shown in Table 1.

Example 5 154 g of 0.1% concentration nitric acid and 14 g of acrylonitrile were added to 7 g of absolutely dried softwood kraft pulp and mixed well. Next, 370 mg of ceric ammonium nitrate was added as a graft polymerization initiator, and graft polymerization was carried out at room temperature for 1 hour. The reaction product was 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. The reaction product was separated by filtration and washed with a 76% aqueous methanol solution,
It was vacuum dried to obtain a hydrolyzate of the graft copolymerized pulp. Next, 5 g of this hydrolyzate was mixed with 50 parts of isopropanol.
ml, 10 ml of water, and 1.5 g of sodium hydroxide were added, 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 stirred at 40 ° C. for 3 hours.
The hydrolysis product was subjected to carboxymethylation by heating for a period of time, washed with 70% methanol, and dried in vacuum. In this way, a hydrolyzate of carboxymethylated graft copolymer pulp was obtained.

3 g of the hydrolyzate of the carboxymethylated graft copolymerized pulp was placed in a vinyl bag, 60 ml of 4N hydrochloric acid was added, and the mixture was mixed for 30 minutes by rubbing by hand from outside the vinyl bag, and left for 30 minutes. . The mixture was filtered to separate the acid-type graft copolymerized pulp, and washing with pure water and filtration were repeated to remove excess acid. This acid type graft copolymerized pulp is placed in a 300 ml beaker, and 150 ml of pure water is added to disperse it. After adding 7.75 ml of 1N sodium hydroxide aqueous solution, it is partially neutralized and swollen with stirring to form a gel. Let The conversion rate to the salt type under this swelling condition was 70%, and the swelling degree of the graft copolymerized pulp was 28 g / g. The mixture was filtered to separate the gel and transferred to a 200 ml beaker. After adding 90 ml of methanol to this gel and dispersing,
1.16 ml of a 2N sodium hydroxide methanol solution was added, and the remaining acid-type carboxyl groups were returned to the salt-type while stirring. After standing for 1 hour, the gel is filtered to 100%
100 ml of methanol was added to replace the water in the gel and remove it. Allow to stand for 1 hour, filter the gel and re-fill 100%
After washing with methanol and drying, a fibrous water absorbent material was obtained. Using this material, the artificial urine water absorption and gel strength were measured, and the results are shown in Table 1.

Example 6 To 10 g of the commercially available powdery CMC sodium salt, 3 g of sodium hydroxide and 80 g of water were added, and the mixture was stirred and mixed for 1 hour to form C.
The MC was dissolved. Next, 3 g of epichlorohydrin was added and further stirred and mixed for 1 hour, and then a crosslinking reaction was carried out at 40 ° C. for 6 hours. The resulting gel was cut to a size of 10 × 5 × 1 mm and stirred in 500 ml of 70% methanol for 2 hours. The gel is filtered and 100% methanol 500m
After stirring for 1 hour in 1 l, it was filtered again and dried in a vacuum oven at 50 ° C. This was crushed to obtain a particulate crosslinked CMC sodium salt. This crosslinked CMC sodium salt was treated in the same manner as in Example 1 to obtain a particulate water absorbent material. Using this material, the artificial urine water absorption and gel strength were measured, and the results are shown in Table 1.

Example 7 When a crosslinked CMC having an acid type carboxyl group was partially neutralized with an alkali and swollen to form a gel, 2.21 ml of a 1N aqueous sodium hydroxide solution was added and used. A fibrous water absorbent material was obtained in the same manner as in Example 1 except for the above, and the water absorption of artificial urine and gel strength were measured using this material, and the results are shown in Table 1. The conversion rate to the salt form under the swelling conditions used was 20%, and the swelling degree of the crosslinked CMC was 4 g / g.

Comparative Example 1 The artificial urine water absorption and gel strength were measured using the fibrous crosslinked CMC sodium salt obtained in Example 1 and before being converted into the acid form, and the results are shown in Table 1. It was

Comparative Example 2 The artificial urine water absorption and gel strength were measured using the fibrous crosslinked CMC sodium salt obtained in Example 3 and before conversion to the acid form, and the results are shown in Table 1. It was

Comparative Example 3 The artificial urine water absorption and gel strength were measured using the powdered, cross-linked HECMC sodium salt obtained in Example 4 and before conversion to the acid form, and the results are shown in Table 1. It was

Comparative Example 4 The artificial urine water absorption and gel strength were measured using the fibrous graft-polymerized CMC sodium salt obtained in Example 5 and before being converted into the acid form, and the results are shown in Table 1. Indicated.

Comparative Example 5 The artificial urine water absorption and gel strength were measured using the particulate crosslinked CMC sodium salt obtained in Example 6 and before being converted to the acid form, and the results are shown in Table 1. It was

Comparative Example 6 When a crosslinked CMC having an acid type carboxyl group was partially neutralized with an alkali and swollen to form a gel, 1.11 ml of a 1N sodium hydroxide aqueous solution was added. A fibrous water absorbent material was obtained in the same manner as in Example 1 except that the above was used, and the artificial urine water absorption and gel strength were measured using this material, and the results are shown in Table 1. The conversion rate to the salt form under the swelling conditions used was 10%, and the swelling degree of the crosslinked CMC was 2 g / g.

Comparative Example 7 When a crosslinked CMC having an acid type carboxyl group was partially neutralized with an alkali and swollen to form a gel, 8.86 ml of a 1N sodium hydroxide aqueous solution was added for use. The same process as in Example 1 was carried out except that the above was performed. However, since the degree of swelling was too high and the gel became extremely soft, the gel could not be separated by filtration, and a superabsorbent material could not be obtained. The conversion rate to the salt type was 80% under the swelling conditions used.
Thus, the swelling degree of the crosslinked CMC was 60 g / g.

Comparative Example 8 A crosslinked CMC having an acid type carboxyl group was partially neutralized with an alkali to swell to form a gel.
A fibrous water-absorbing material was obtained in the same manner as in Example 1 except that the remaining acid-type carboxyl groups in the gel were not returned to the salt-type, and using this material, the artificial urine water absorption and gel strength were obtained. Was measured and the results are shown in Table 1.

Comparative Example 9 The same operation as in Example 1 was carried out to partially neutralize the crosslinked CMC having an acid-type carboxyl group with an alkali to swell the gel to form a gel. After changing the carboxyl groups of the above to the salt form, the gel was filtered. afterwards,
A solid resinous water-absorbent material was obtained by drying without removing water in the gel by replacing with methanol, and the artificial urine water absorption and gel strength were measured using this material, and the results are shown in Table 1. Indicated.

COMPARATIVE EXAMPLE 10 3 g of the fibrous crosslinked CMC sodium salt obtained in Example 1 was used, and the gel was swollen with 63.3 g of a 48.8% aqueous isopropanol solution without changing the carboxyl group to the acid form. Was produced, and water was removed in the same manner as in Example 1 to obtain a fibrous water-absorbing material. Using this material, the artificial urine water absorption and gel strength were measured, and the results are shown in Table 1.
It was shown to. The swelling degree of the crosslinked CMC under this swelling condition was 5 g / g.

[0058]

[Table 1]

As can be seen from Table 1, the superabsorbent material comprising the cellulose derivative according to the present invention has a high water absorption amount of artificial urine and an excellent gel strength (Examples 1 to 7). On the other hand, the crosslinked cellulose derivative having a salt type carboxyl group before being converted to the acid type has a slightly low water absorption amount or is equivalent, but has extremely poor gel strength (Comparative Examples 1 to 1).
5), not suitable for practical use. When the degree of swelling is low even with the same method as in the present invention (Comparative Example 6), the water absorption is about the same,
The gel strength is low, and when the carboxyl group of the cellulose derivative is not acidified but swelled with an alcohol-water solvent in a salt form to form a gel (Comparative Example 10), the water absorption is remarkably high, but the gel strength is high. Both are low and not suitable for practical use. If the degree of swelling is made too high according to the same method as in the present invention (Comparative Example 7), the produced gel becomes so soft that it cannot be separated by filtration and cannot be treated. On the other hand, even if a gel is formed by partial swelling due to neutralization, the remaining acid-type carboxyl groups may not be returned to the salt-type (Comparative Example 8).
Alternatively, after the gel produced by filtration is separated and the water remaining in the gel is dried without being replaced with an organic solvent that is compatible with water such as methanol (Comparative Example 9), the water absorption and gel strength are also It was bad and could not be put to practical use.

[0060]

INDUSTRIAL APPLICABILITY The present invention can be synthesized with a relatively small amount of organic solvent, exhibits high water absorption not only in pure water but also in an aqueous solution containing various salts, and has excellent gel strength after water absorption. Since it is easy to handle, the present invention has an effect of providing a method for producing a water-absorbing material composed of a cellulose derivative which can be suitably used in a wide range of fields, especially as a hygiene material.

Claims (1)

[Claims] 1. A cellulose derivative, which is water-insolubilized by cross-linking and has all carboxyl groups in an acid form, is dispersed in water, and then an alkali is added to neutralize the carboxyl groups to have a swelling degree of 3 to 30 g / g. Of the cellulose derivative gel, and then the gel is separated from water and placed in an organic solvent compatible with water, alkali is added to restore the acid-type carboxyl groups remaining in the gel to the salt form, Further, after separating the gel from the solvent, the water in the gel is replaced with the organic solvent to remove the gel, and the gel is dried, which is excellent in salt water absorption capacity and gel strength. Manufacturing method.