JPH08243388A - Production of water absorbing cellulosic material - Google Patents

Abstract

PURPOSE: To produce a water absorbing cellulosic material having a high rate of absorption while maintaining high water absorption even to an aq. soln. contg. various salts through simple processes at a low cost. CONSTITUTION: A water-swellable cellulose deriv. having carboxyl groups and bonded by cross-linking is immersed in a 0.2-4N aq. soln. of a strong acid at 5-40 deg.C for 20-180min. The cellulose deriv. is then put in an org. solvent compatible with water, an alkali is added to restore acid type carboxyl groups to salt type ones and drying is carried out. The strong acid is hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, phosphoric acid or a mixture of these acids.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention not only has an excellent salt water absorption rate, but also has an excellent ability to retain salt water that has been once absorbed. Therefore, various sanitary materials, agricultural materials, food packaging materials, civil engineering materials, etc. The present invention relates to a method for producing a water-absorbing cellulose material which is useful in a wide range of fields such as building 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 aqueous solutions containing salts such as water or 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, non-woven fabric, sponge, etc., which are known as traditional water-absorbing materials, absorb water by a capillary phenomenon, whereas the above-mentioned highly water-absorbent resin absorbs water. Since the principle is osmotic pressure, it can absorb much more water than capillarity.
Further, the highly water-absorbent resin has a feature that the gel does not easily re-emit water even when pressure is applied in a water-absorbing state, which is excellent in gel strength. 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, these superabsorbent resins have a slow absorption rate and cannot cope with the case where a large amount of liquid needs to be absorbed in a short time such as a disposable diaper. It is necessary to use it in combination with the type of material. Further, the super absorbent resin has a drawback that when it is used for a solution containing a salt such as saline or urine, the osmotic pressure, which is the driving force of water absorption, is reduced, and the water absorption amount is significantly reduced. There is.

As described above, the conventional super absorbent resin is
It has two drawbacks: a low water absorption rate and a low water absorption of a salt-containing solution. Therefore, various attempts have been made. For example, unlike synthetic polymers such as sodium polyacrylate, polysaccharides do not have thread-like molecules even in salt water and can maintain a relatively wide conformation. Has been. That is, a method of graft-polymerizing a hydrophilic monomer onto a polysaccharide (Japanese Patent Laid-Open No. 56-76).
419, JP-A-56-76481), and a method of crosslinking the polysaccharide itself (JP-A-56-5137, JP-A-58-79006, and JP-A-60-58).
No. 443) is known.

Further, a method using a cellulose derivative (in particular, carboxymethyl cellulose is often used) as a polysaccharide (JP-A-49-128987, JP-A-50-85689, JP-A-54-163981). , JP-A-56-28755, JP-A-58-1
No. 701, JP-A-60-94401, JP-A-61-89364, etc.) have also been studied. On the other hand, the present inventors have found that JP-A-5-49925, JP-A-5-123573, and JP-A-6-172.
No. 401, Japanese Patent Application No. 6-174174 proposes a method for producing a superabsorbent cellulose material in which a carboxymethyl cellulose derivative is cross-linked and has an improved ability to absorb salt water, and the water absorption amount of salt water is increased by these production methods. I was able to make a marked improvement. However, in these production methods, the absorption rate was still at the same level as that of the conventional super absorbent polymer.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, the inventors of the present invention have conducted extensive studies to solve the drawbacks of the prior art, and as a result, have water-swellable cellulose derivatives having a carboxyl group and being cross-linked. It was found that the above-mentioned cellulose derivative material obtained by immersing the above in a strong acid aqueous solution and then converting the carboxyl group into a salt form has a high absorption amount of salt water, and particularly an excellent absorption rate, and has completed the present invention. An object of the present invention is to provide a method capable of inexpensively producing a water-absorbing cellulosic material having an excellent salt water absorption rate with a simple process while maintaining a high water absorption amount.

[0008]

The first object of the present invention is to provide a water-swellable cellulose derivative having a carboxyl group and having a cross-linking bond with an aqueous solution of a strong acid having a concentration of 0.2 to 4 N, and a concentration of 5 to 4
After dipping at a temperature of 0 ° C. for 20 to 180 minutes, and then adding an alkali to the cellulose derivative in an organic solvent having compatibility with water to restore the acid-type carboxyl group to the salt-type,
A method for producing a water-absorbing cellulose material having an excellent salt water absorption rate, which is characterized by drying. The second aspect of the present invention is
The method for producing a water-absorbing cellulose material according to the first aspect of the present invention is characterized in that the strong acid is one selected from hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, phosphoric acid, or a mixture thereof.

The cellulose derivatives used in the present invention include carboxymethyl cellulose (hereinafter abbreviated as CMC), carboxymethyl hydroxyethyl cellulose,
An example is water-soluble cellulose derivative having a carboxyl group, such as carboxyethyl cellulose, which is crosslinked to impart water swelling property, and is appropriately selected and used from these. The method of crosslinking the cellulose derivative is not particularly limited, and known methods such as a method of crosslinking by heating (thermal crosslinking) and a method of reacting a crosslinking agent can be used. As cross-linking agents, aldehydes such as formaldehyde and glyoxal; N-methylol compounds such as dimethylolurea, dimethylolethyleneurea and dimethylolimidazolidone; polycarboxylic acids such as oxalic acid, maleic acid, succinic acid and polyacrylic acid Acids; polyvalent epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and diepoxybutane; divinyl compounds such as divinyl sulfone and methylenebisacrylamide; polyvalent compounds such as dichloroacetone, dichloropropanol and dichloroacetic acid Halogen compounds; halohydrin compounds such as epichlorohydrin and epibromohydrin; and polyvalent aziridine compounds can be used.

The cellulose derivative used in the method of the present invention is a water-absorbing material produced by graft-copolymerizing cellulose or a cellulose derivative with a monomer, 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 water-soluble cellulose derivative, non-electrolyte-based cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose and acetyl cellulose can be used. Examples of the monomer to be graft-copolymerized are acrylic acid, methacrylic acid and monomers having a carboxyl group such as alkali metal salts thereof, acrylamide, methacrylamide, acrylonitrile, methyl acrylate, ethyl acrylate, methacrylic acid. A monomer containing a group that produces a carboxyl group by hydrolysis such as methyl or ethyl methacrylate can be used.

The cross-linking treatment may be carried out before or after the graft polymerization, and may be carried out by the same method as in the case of the electrolyte-based water-soluble cellulose derivative. A copolymerizable divinyl compound such as N, N'-methylenebisacrylamide,
The graft copolymerization may be carried out in the presence of N, N'-methylenebismethacrylamide, ethylene glycol diacrylate and the like. The shape of the crosslinked cellulose derivative is not particularly limited, such as fibrous, powdery, particulate, and sheet-like, but when fibrous ones are used, the absorption effect due to the capillary phenomenon is added, so that the absorption rate is particularly excellent. A water absorbent material is obtained.

In the present invention, first, the cellulose derivative crosslinked as described above (hereinafter referred to as cellulose derivative) is immersed in an aqueous solution of 0.2 to 4 N strong acid at a temperature of 5 to 40 ° C. for 20 to 180 minutes. To do. As the strong acid,
Examples thereof include hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, and phosphoric acid, and these are preferably used alone or as a mixture. Acetic acid, weak acid such as citric acid does not exert the effect of the present invention, when the cellulose derivative is immersed in the aqueous solution,
This is inconvenient because the cellulose derivative is often swollen and cannot be subjected to treatment such as filtration and washing after immersion. The acid concentration of the strong acid aqueous solution needs to be in the range of 0.2 to 4 N. If the acid concentration is less than 0.2 N, the effect of the present invention cannot be obtained, and the cellulose derivative may dissolve or swell, which is not suitable. If the acid concentration exceeds 4 N, the cellulose derivative will be hydrolyzed and it will be difficult to remove excess acid, which is not preferable. The addition amount of the strong acid aqueous solution is determined in relation to the acid concentration,
It may be added within the range of 10 to 150 kg / kg of cellulose derivative.

Cellulose derivatives are often produced in a state where the carboxyl group is an alkali metal salt. In that case, when the cellulose derivative is immersed in a strong acid aqueous solution, the carboxyl group is converted from the salt form to the acid form, and the acid is consumed together with the decrease in the acid concentration. The concentration needs to be maintained between 0.2 and 4 N, and the acid concentration and addition amount of the acid aqueous solution must be determined in consideration of such points. The time for immersing the cellulose derivative in the strong acid aqueous solution is 20 to 180 minutes, although it varies depending on the acid concentration. When the acid concentration is low, the immersion requires a long time, and when the acid concentration is high, a short time is sufficient. However, if the immersion time is less than 20 minutes, the effect of the present invention cannot be obtained even if the acid concentration is increased, and conversely, if the immersion time is 180 minutes or more, the water absorption amount becomes too small, which is not suitable. The higher the acid concentration and the longer the immersion time, the absorption rate
Although it tends to be faster, the amount of water absorption decreases at the same time, so it is necessary to adjust it according to the specifications required for the water absorbent material.

The temperature at which the cellulose derivative is immersed in the strong acid aqueous solution is in the range of 5 to 40 ° C. Cellulose derivatives are easily hydrolyzed by acids, and the hydrolysis rate increases remarkably at high temperatures. When the molecular weight of the cellulose derivative decreases due to hydrolysis, the water absorption decreases, so temperatures above 40 ° C are not suitable. It is also not suitable for extremely low temperatures where the acid freezes. Next, the cellulose derivative immersed in the strong acid aqueous solution by the method described above is separated from the acid aqueous solution by filtration, dehydration, etc., and dispersed in an organic solvent compatible with water. Before dispersing the dipping-treated cellulose derivative in an organic solvent that is compatible with water, it is better to remove excess acid attached by washing with water so that the amount of alkali used in the next step is smaller. Then
It is desirable because it reduces the amount of inorganic salts contained in the product.

As the organic solvent compatible with water, one having a high alkali solubility is desirable, and methanol or ethanol is preferable. These organic solvents may contain some water, but the amount should be 20% by weight or less. When the content of water is large, the cellulose derivative causes swelling when the acid-type carboxyl group is returned to the salt-type by using an alkali, which makes subsequent treatment difficult, which is not suitable. The amount of the organic solvent compatible with water added is 20 to 100 kg / kg of cellulose derivative.
If the amount added is small, the salt form will not be uniform, and if it is too large, the cost of the organic solvent will increase, which is not suitable. Then, an alkali is added to the cellulose derivative dispersed in an organic solvent compatible with water to return the acid-type carboxyl group to the salt-type. Examples of the alkali include sodium hydroxide, lithium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide and the like, and are appropriately selected and used from these, but it is preferable to use inexpensive sodium hydroxide. It is suitable.

The amount of alkali to be added may be calculated from the amount of carboxyl groups contained in the cellulose derivative, and the necessary amount may be added. To add an excess alkali, an extra step for removing the excess alkali is required. It should be avoided if possible. The alkali may be added as a solid, but in that case it takes time to dissolve the solid, so it is preferable to dissolve the alkali in an organic solvent compatible with water in advance. After returning the carboxyl group to the salt form, the water-absorbent cellulose material can be obtained by filtering and drying. If necessary, wash the water-absorbent cellulosic material with an organic solvent that is compatible with water before drying, to remove water, inorganic salts,
Residual alkali may be removed. Particularly, by completely removing the water content, it is possible to prevent the water-absorbent cellulose material after drying from becoming a hard resinous material.

The reason why the water-absorbent material having an excellent absorption rate can be obtained by the method of the present invention is not yet clear, but some chemical reaction may occur in the network structure of the cellulose derivative molecule while the cellulose derivative is immersed in the aqueous solution of strong acid. It is considered that a change or a reaction occurs, and thereby a structure suitable for the absorption rate is changed, so that it becomes an absorbent material excellent in both the absorption rate and the water absorption amount. It goes without saying that the carboxyl group of the cellulose derivative changes from the salt type to the acid type when immersed in an aqueous solution of a strong acid. It's already done. However, it was found that the properties of the obtained water-absorbent material are changed by continuing the immersion even after the carboxyl group is completely changed to the acid form. According to the method of the present invention, the longer the immersion time of the cellulose derivative in the aqueous solution of strong acid, the higher the absorption rate of the water-absorbing material with respect to salt water, the lower the water absorption amount, and the higher the strength of the absorbed gel. Can be seen. This change can be explained well by considering that it is caused by the formation of new cross-links. The resulting cross-linking bond may be an ester bond between a carboxyl group and a hydroxyl group, and it is considered that the acid acts as a catalyst for it.

In view of the fact that a water-absorbing material having an excellent absorption rate cannot be obtained by treating with a weak acid such as acetic acid in the same manner as in the method of the present invention, in the molecular structure of the cellulose derivative as described above. It is considered that the chemical change may or may not occur due to the strength of its catalytic ability. As described in detail above, the reason why the water absorbent material according to the present invention exhibits an excellent absorption rate is that the network structure of the cellulose derivative molecule is changed by the cross-linking bond newly formed in the cellulose derivative. Such changes contribute to the improvement of the absorption rate of the water-absorbent material, and the water-absorbent material also maintains an excellent water absorption amount.

The second reason why the water absorbent material having an excellent absorption rate can be obtained by the method of the present invention is the reduction of the water-soluble component in the water absorbent material. The crosslinked cellulose derivative used in the method of the present invention is synthesized by crosslinking the 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 will cause stickiness, residue, etc. when the gel is swollen, and the absorption rate will be reduced. It also leads to a decrease in water absorption and gel strength. Therefore, it is theoretically necessary to increase the crosslink density as much as possible and remove the water-soluble component. In the method of the present invention, since the low molecular weight water-soluble component can be eluted and removed in the step of immersing the cellulose derivative in the aqueous solution of strong acid, this also further enhances the improvement of the absorption rate of the water-absorbing material. .

[0020]

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

Example 1 Softwood bleached kraft pulp having an absolute dry weight of 20 g was defibrated 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 ml of water to it.
And 6.20 g of sodium hydroxide were mixed and stirred for 1 hour to obtain alkali cellulose. To this, 17.3 g of sodium monochloroacetate and 0.6 g of epichlorohydrin were added, stirred for 30 minutes, and allowed to stand 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 is filtered through a glass filter (2G), thoroughly washed with 70% methanol,
It was washed twice with 100% methanol and dried in a vacuum dryer to obtain 30 g of fibrous crosslinked carboxymethyl cellulose (hereinafter referred to as CMC) sodium salt (degree of substitution 1.0).

Cross-linked CM in a 500 ml beaker
Take 3 g of C sodium salt, and add 30 mL of 1N hydrochloric acid at 25 ° C.
Add 0 ml, stir for 30 minutes, leave for 30 minutes, total 60
Soaked for a minute. This mixture is a glass filter (2G)
Cross-linked CM having acid type carboxyl group after filtration with
C was separated, and washing and filtration were repeated with pure water to remove excess acid. 30% of this acid type crosslinked CMC
The mixture was transferred to a 0 ml beaker, 150 ml of methanol was added and dispersed, 10 ml of a 1N sodium hydroxide-methanol solution was added, and the mixture was stirred for 1 hour to return the acid-type carboxyl group to the salt-type. The mixture was filtered through a glass filter (2G) and washed once with methanol, then 40
It was dried in a vacuum dryer at 0 ° C. to obtain a fibrous water absorbent material.
Using the obtained water-absorbent cellulose material, the absorption rate and water absorption of artificial urine were measured by the test methods shown below, and the quality thereof was evaluated.

Test method (1) Absorption rate A circular shape having a diameter of 15 cm and a basis weight of 200 g / m ² ,
Two mats of bleached softwood kraft pulp having a density of 0.075 g / cm3 were prepared. This mat is fluffed pulp obtained by defibrating bleached softwood kraft pulp with a household mixer, and using this as a mat forming device (diameter 15 cm with a 150 mesh stainless wire stretched at the bottom, length 50 c).
m acrylic tube) to suck a small amount to form a mat, and then press to adjust the density to the above. 3 g of the obtained water-absorbent cellulose material was evenly dispersed between the two mats to obtain a measurement sample.

On this measurement sample, a stainless plate having a hole in the center (size 10 cm × 10 cm, weight 665 g,
A hole having a diameter of 25 mm) was placed, and artificial urine was absorbed through a hole in a stainless steel plate from a separating funnel containing 25 ml of artificial urine having the following composition, and the time until 25 ml was completely absorbed was measured. When absorbing artificial urine, it is necessary to take care so that it does not overflow from the holes in the stainless steel plate. After the first absorption, remove the stainless steel plate, leave it for 30 minutes, place the stainless steel plate again, absorb artificial urine by the same operation as the first time, and measure the second absorption time in the same manner as the first time. did. Similarly, after the second absorption was completed, the stainless steel plate was removed, left for 30 minutes, the stainless steel plate was placed again, and the third absorption time was measured in the same manner as the first absorption.

As described above, a total of 75 ml of artificial urine was absorbed three times, and the total absorption time was defined as the absorption rate. An absorption rate of less than 140 seconds was evaluated as good. Artificial urine composition Ingredient% by weight Urea 2.00 Sodium chloride 0.80 Magnesium sulfate 7-hydrate 0.08 Calcium chloride dihydrate 0.03 Pure water 97.09

(2) Water Absorption of Artificial Urine Solution The water-absorbent material obtained was used as a test sample, and 0.8 g of the water-absorbent material was sealed in a bag made of 250-mesh nylon wire of 10 cm square and having the above composition. It was immersed in artificial urine for 10 minutes to absorb water. This is pulled up and suspended, 10
After water was drained for a minute, the weight was measured, and the water absorption amount was indicated by the weight of the artificial urine absorbed per 1 g of the sample dried. A water absorption of more than 20 g / g was evaluated as good.

Example 2 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker, and 300 ml of 3N hydrochloric acid at 25 ° C. was added.
Put in, stir for 30 minutes, leave for 30 minutes, soak time 60
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the time was changed. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Example 3 3 g of crosslinked CMC obtained in the same manner as in Example 1 was placed in a 500 ml beaker, and 300 mL of 0.5N hydrochloric acid at 25 ° C. was used.
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that 30 ml was added, the mixture was stirred for 30 minutes, left for 30 minutes, and immersed for 60 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Example 4 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker and 300 ml of 1N hydrochloric acid at 25 ° C.
Stir for 30 minutes, leave for 90 minutes, soak time 12
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the time was set to 0 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Example 5 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker, and 300 ml of 1N hydrochloric acid at 25 ° C. was added.
A water-absorbent cellulosic material was produced in the same manner as in Example 1 except that the mixture was added, stirred for 30 minutes, immediately filtered, and immersed for 30 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Example 6 Commercially available powdered CMC sodium salt (degree of substitution 0.65, 1
% Aqueous solution viscosity: 280 cps, trade name: Serogen WS
-C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 30 g of isopropanol 33
3 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. The reaction mixture is then neutralized with acetic acid and filtered to remove most of the reaction solvent,
Hydroxyethyl carboxymethyl cellulose sodium salt (hereinafter referred to as HECMC sodium salt) was prepared by drying at 0 ° C. for 4 hours. 30g of this HECMC sodium salt was put into a reaction vessel, and 600m of isopropanol was added.
1, 120 ml of water and 4.5 g of ethylene glycol diglycidyl ether were mixed. 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 product mixture was filtered through a glass filter (2G), thoroughly washed with 70% methanol, and then 1
It was washed twice with 00% methanol and dried in a vacuum dryer to obtain a crosslinked HECMC sodium salt.

The above cross-linked HECMC was added to a 500 ml beaker.
Take 3g of sodium salt and add 1N of 1.5N sulfuric acid at 15 ℃.
50 ml was added, stirred for 30 minutes and left for 30 minutes, and the immersion time was set to 60 minutes. This mixture was filtered to separate HECMC having an acid type carboxyl group, and washing and filtering were repeated with pure water to remove excess acid. Transfer the acid type cross-linked HECMC to a 300 ml beaker,
After 100 ml of ethanol was added and dispersed, 6.4 ml of 1N sodium hydroxide methanol solution was added and stirred for 1 hour to restore the acid-type carboxyl group to the salt-type. This mixture was filtered through a glass filter (2G), washed once with ethanol, and then dried in a vacuum dryer at 40 ° C to obtain a powdery water-absorbing material. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Example 7 154 g of 0.1% concentration nitric acid and 14 g of acrylonitrile were added to a bleached softwood kraft pulp having an absolute dry weight of 7 g, and they were 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 and dehydrated, then 3% aqueous sodium hydroxide solution (1000 m)
1 was added and the graft copolymerized pulp was hydrolyzed by heating at 100 ° C. for 2 hours. The reaction product was separated by filtration, washed with a 76% aqueous methanol solution, and then vacuum dried to obtain a hydrolyzate of the graft copolymerized pulp. Next, 5 g of this hydrolyzate was mixed with 5 parts of isopropanol.
0 ml, 10 ml of water and 1.5 g of sodium hydroxide were added, the mixture was stirred at room temperature for 1 hour, 4.4 g of sodium monochloroacetate was added, and this mixture was further heated at 40 ° C. for 3 hours to obtain the hydrolyzate. Was subjected to carboxymethylation, washed with 70% methanol, and dried in vacuum. A hydrolyzate of carboxymethylated graft copolymer pulp was obtained.

Into a 500 ml beaker, 3 g of the carboxymethylated graft copolymerized pulp hydrolyzate was placed, and 100 ml of 2.5 N nitric acid at 10 ° C. was added to the beaker to make 30
Stir for minutes. This mixture was filtered to separate the graft copolymerized pulp having an acid type carboxyl group, and washing and filtration were repeated with pure water to remove excess acid.
Transfer the graft copolymerized pulp having the acid type carboxyl group to a 300 ml beaker, and add 100 ml of methanol.
Then, 12 ml of 1N sodium hydroxide-methanol solution was added and the mixture was stirred for 1 hour to restore the acid type carboxyl group to the salt type. The mixture was filtered through a glass filter (2G), washed once with methanol, and then dried in a vacuum dryer at 40 ° C to produce a fibrous water-absorbent cellulose material. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Comparative Example 1 The absorption rate and water absorption of artificial urine were measured using the fibrous, crosslinked CMC sodium salt obtained in Example 1 and before its acid form, and its quality was evaluated. .

Comparative Example 2 The absorption rate and water absorption of artificial urine were measured using the powdered, cross-linked HECMC sodium salt obtained in Example 6 before conversion to the acid form, and its quality was evaluated. .

Comparative Example 3 The absorption rate and water absorption of artificial urine were measured using the fibrous, graft-polymerized CMC sodium salt obtained in Example 7, which was not acidified, and its quality was evaluated. did.

Comparative Example 4 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker, and 300 ml of 1N acetic acid at 25 ° C. was added.
Put in, stir for 30 minutes, leave for 30 minutes, soak time 60
When the time was set to minutes, the cross-linked CMC swelled, filtration could not be performed, and a water-absorbent cellulose material could not be obtained.

Comparative Example 5 3 g of crosslinked CMC obtained in the same manner as in Example 1 was placed in a 500 ml beaker and 300 g of 2N citric acid at 25 ° C. was added.
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that 30 ml was added, the mixture was stirred for 30 minutes, left for 30 minutes, and immersed for 60 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Comparative Example 6 3 g of crosslinked CMC obtained in the same manner as in Example 1 was placed in a 500 ml beaker and 300 ml of 1N hydrochloric acid at 25 ° C.
A water-absorbent cellulosic material was produced in the same manner as in Example 1 except that the mixture was added and stirred for 10 minutes, then immediately filtered, and the immersion time was changed to 10 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Comparative Example 7 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker and 300 ml of 25 ° C. 1N hydrochloric acid was added.
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the mixture was stirred for 30 minutes, left for 210 minutes, and immersed for 240 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Comparative Example 8 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker and 300 ml of 1N hydrochloric acid at 50 ° C.
Stir for 30 minutes, leave for 30 minutes, soak time 6
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the time was set to 0 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Comparative Example 9 3 g of crosslinked CMC obtained in the same manner as in Example 1 was placed in a 500 ml beaker and 300 mL of 0.1N hydrochloric acid at 25 ° C. was added.
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that 30 ml was added, the mixture was stirred for 30 minutes, left for 30 minutes, and immersed for 60 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

Comparative Example 10 3 g of crosslinked CMC obtained by the same method as in Example 1 was placed in a 500 ml beaker and 300 ml of 5N hydrochloric acid at 25 ° C.
Stir for 30 minutes, leave for 30 minutes, soak time 6
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the time was set to 0 minutes. The absorption rate of the artificial urine and the amount of water absorption of the obtained water-absorbent cellulose material were measured, and the quality thereof was evaluated.

The results obtained are shown in Table 1.

[0046]

[Table 1]

As can be seen from Table 1, the water-absorbent cellulose material according to the present invention has a remarkably high absorption rate of artificial urine, and also has a water absorption amount which is substantially the same as that of the cross-linked cellulose material before treatment. (Examples 1 to 7). On the other hand, the known crosslinked cellulosic material has a remarkably slow absorption rate and is not suitable for use in which a large amount of urine must be absorbed in a short time such as a disposable diaper (Comparative Examples 1 to 1).
3). Even with the same technique as the present invention, if a weak acid is used,
Even if the treatment cannot be performed in the next step, or even if the treatment can be performed, the absorption rate of the water-absorbent cellulose material cannot be improved (Comparative Examples 4 to 5). Even when hydrochloric acid as a strong acid that can be preferably used in the present invention is used, the water absorption amount is excellent when the immersion time is short (Comparative Example 6) and the acid concentration is too low (Comparative Example 9). However, when the water absorption rate is not improved, while the immersion time is too long (Comparative Example 7) and the acid temperature or concentration during treatment is too high (Comparative Examples 8 and 10), the water absorption rate of the water-absorbing cellulose material is Although it can be remarkably improved, it is not suitable for practical use because the water absorption becomes extremely poor (20 g / g or less).

[0048]

INDUSTRIAL APPLICABILITY The present invention is capable of quickly absorbing an aqueous solution containing various salts such as artificial urine, and has an excellent water absorption amount, and is suitable for use in a wide range of fields, especially for sanitary materials. The effect of providing a method for producing a water-absorbing cellulose material that can be obtained is exerted.

Claims (2)

[Claims] 1. A water-swellable cellulose derivative having a carboxyl group and which is cross-linked, is immersed in an aqueous solution of a strong acid of 0.2 to 4 N at a temperature of 5 to 40 ° C. for 20 to 180 minutes, and then, The water-soluble cellulose having an excellent salt water absorption rate, which is characterized in that the cellulose derivative is added with an alkali in an organic solvent having compatibility with water to restore the acid type carboxyl group to the salt type, and then dried. Material manufacturing method. 2. The method for producing a water-absorbing cellulose material according to claim 1, wherein the strong acid is one selected from hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, phosphoric acid, or a mixture thereof. .