JPH10204101A - Biodegradable water-absorbing material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing material which has high biodegradability and is excellent in the ability to absorb an electrolyte solution and a process for producing the same. SOLUTION: This material comprises a polycarboxylic acid cellulose derived by replacing at least part of the hydroxyl groups of the glucose rings constituting cellulose by a polycarboxylic acid as part of the cellulose skeleton. It is desirable that the polycarboxylic acid cellulose is one in which part of the carboxyl groups are in the form of an alkali metal salt and that part of the cellulose skeleton has a crosslinkage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly water-absorbing material having excellent biodegradability, and more particularly to a biodegradable material having excellent water absorption of an electrolyte solution.

[0002]

2. Description of the Related Art Biodegradable water-absorbing materials include:
Cellulose such as pulp and paper, starch and sodium salts of carboxymethyl cellulose are known. However, these water-absorbing materials utilize the capillary action or thickening of water, and thus have a disadvantage that the water-absorbing power decreases when pressure is applied from the outside. On the other hand, as a material with biodegradability and excellent water absorption,
There have been proposed ones utilizing polysaccharides, for example, those obtained by graft-polymerizing a hydrophilic monomer onto a polysaccharide (Japanese Patent Laid-Open No.
No. 6-76419) and those obtained by crosslinking polysaccharides themselves (JP-A-56-5137, JP-A-60-5).
No. 8443) and the like. As polysaccharides, those crosslinked using cellulose derivatives (JP-A-49-128879, JP-A-50-85689).
JP, JP-A-54-163981, JP-A-56-163981
-28755, JP-A-57-137301, JP-A-58-1701, JP-A-60-944
No. 01, JP-A-61-89364 and JP-A-Hei-4
-164311, JP-A-5-49925,
A number of proposals have been made in JP-A-5-123573.

[0003]

However, conventional materials comprising the above-mentioned graft polymer or cross-linked product of the polysaccharide and the cellulose derivative are more biodegradable than the natural polysaccharides and the celluloses as starting materials. In order to maintain their biodegradability at a high level, a reduction in water absorption was inevitable. Also, recently, after crosslinking the alkali metal salt of carboxyalkyl cellulose itself,
A superabsorbent material having relatively good biodegradability obtained by heat treatment has been proposed (JP-A-7-82301).
However, this water absorbing material has a problem that the water absorption of the electrolyte solution is low. Therefore, there is a demand for a water-absorbing material having the same biodegradability as a natural substance and at the same time, having high water absorption of an electrolyte solution.

The present invention has been made to solve the above-mentioned problems in the conventional technology. That is, an object of the present invention is to provide a water-absorbing material which has high biodegradability and also has excellent biodegradability in water absorption of an electrolyte solution, and a method for producing the same.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and found that a novel cellulose derivative having a specific chemical structure is useful as a biodegradable water-absorbing material. The inventors have found that the present invention has been completed. That is, the biodegradable water-absorbing material of the present invention includes, as a part of the cellulose skeleton, a polyvalent carboxylate glucose in which at least a part of the hydroxyl group of a glucose ring constituting cellulose is substituted by a polyvalent carboxylic acid. It is characterized by comprising a polyvalent cellulose carboxylate. And, in the present invention, it is preferable that a part of the carboxyl group of the cellulose polycarboxylate is a biodegradable water-absorbing material which is an alkali metal salt, and a part of the cellulose skeleton. It is preferably a biodegradable water-absorbing material having a crosslinked structure.

The process for producing a biodegradable water-absorbing material according to the present invention comprises reacting cellulose with a halogen-substituted polycarboxylic acid to form a polycarboxylic acid containing glucose as a part of the cellulose skeleton. It is characterized in that acid cellulose is formed, and then the obtained polyvalent carboxylic acid cellulose is reacted in the presence of a crosslinking agent.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, as a raw material for producing polyvalent carboxylate, cellulose obtained by a known method, such as one extracted from a plant containing cellulose such as wood pulp or recycled pulp, is used. The novel polyvalent carboxylic acid cellulose used in the present invention is obtained by introducing a polyvalent carboxylic acid into the above-mentioned cellulose, and a halogenated polyvalent carboxylic acid capable of forming an ether bond with the cellulose. It can be produced by a known etherification reaction using an acid. This etherification is generally performed by reacting cellulose with a polycarboxylic acid.

[0008] The halogenated polycarboxylic acid used in the above reaction is not particularly limited as long as it is a compound having a plurality of carboxyl groups. Examples of dicarboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, malic acid, tartaric acid, and the like.
Examples of the tricarboxylic acid include citric acid, aconitic acid, and camphoronic acid. The halogen atom in the halogenated polycarboxylic acid is not particularly limited as long as it has a halogen atom at a position other than the carboxyl group.

The present invention uses the cellulose polycarboxylate obtained by the above method as a biodegradable water-absorbing material. Therefore, the cellulose polycarboxylate has high biodegradability, It is preferable that the water absorption of the electrolyte solution is large.

In the present invention, the degree of substitution of the hydroxyl group in the cellulose by the polyvalent carboxylic acid is 1.5 or less. If the degree of substitution by the polycarboxylic acid is too large, sufficient biodegradability may not be obtained.On the other hand, in order to increase the water absorption to the electrolyte solution, the number of ionic functional groups is mainly large. Therefore, it is preferable that the biodegradability is as large as possible without impairing the biodegradability. In addition, in order to improve the affinity with water and the like, at least a part of the carboxyl group of the polyvalent carboxylate is preferably an alkali metal salt such as potassium or sodium.

In the present invention, in order to improve the water absorption of the above polyvalent carboxylate, the polyvalent carboxylate is crosslinked to form a crosslinked structure by ether bond in a part of the cellulose skeleton. Is preferred. This crosslinking can be performed by a crosslinking reaction using a conventionally known crosslinking agent. As a crosslinking agent to be used, a known polyfunctional crosslinking agent can be applied, and examples thereof include epichlorohydrin, diglycidylethyl ether, and methylenebisacrylamide.

The crosslinked cellulose polycarboxylate in the present invention has high biodegradability, and is obtained by etherifying a hydroxyl group of a glucose ring of a part of the cellulose skeleton with a crosslinking agent. Can be The degree of crosslinking of the crosslinked cellulose polycarboxylate is 1.5 or less. If the degree of cross-linking is higher, sufficient biodegradability may not be obtained. On the other hand, since the water retention when pressure is applied from the outside increases as the number of crosslinks increases, the water retention is preferably as large as possible.

[0013]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. The water absorption and biodegradability of the obtained polyvalent cellulose carboxylate were measured by the following methods. [Water absorption amount] A 0.2 g sample was placed in a nonwoven fabric tea bag type bag (70 mm x 140 mm), and pure water and 0.9 g of pure water were added.
% Sodium chloride aqueous solution for 24 hours, taken out and suspended for 30 minutes, and the weight (W ₁ ) after excess water solution was drained was measured. Similarly, the weight (W ₂ ) of a tea bag-type bag containing no sample was measured. The amount of water absorption was represented by the weight of the solution absorbed per unit weight of the sample, and was calculated according to the following equation using the measured values obtained. Water absorption (g / g) = (W ₁ −W ₂ −0.2) /0.2 [Biodegradability] The biodegradability was evaluated according to JIS-K6950.
According to the test method, the degree of aerobic biodegradation by activated sludge was evaluated by the residual sample weight or BOD value (biochemical oxygen demand). The degree of biodegradation (D _R ) based on the residual sample weight is 2
The weight of the degraded sample after 8 days is expressed as a percentage and
Weight of remaining sample (R _s ) after day and amount of sample added (A)
Was calculated according to the following equation. Biodegradation (%): D _R = {(A−R _S ) / A} × 100 Further, the biodegradation (D _B ) by BOD was obtained by measuring the BOD value (S )
Using the BOD curve, the BOD value (B) of the test culture solution after 28 days obtained from the BOD curve, and the theoretical oxygen demand (TOD) required for complete oxidation of the sample, the following equation was used. . Biodegradability _{(%): D B = {} (S-B) / TOD} × 10
0

Example 1 10 g of bleached softwood bleached kraft pulp was pulverized with a small mixer into a flocculent material, and then 200 ml of isopropyl alcohol, 20 ml of water and 3.0 ml of sodium hydroxide.
g in a reaction vessel and stirred for 1 hour to obtain alkali cellulose. Add monochlorosuccinic acid 10.0
g was added and the mixture was stirred for 30 minutes and then left for 30 minutes. Next, a reflux condenser was attached to the reaction vessel,
The mixture was heated to near boiling and refluxed for 3 hours. The reaction product thus obtained was sufficiently washed with methanol and then dried to obtain a sodium salt of cellulose succinate.

Next, 10 g of the obtained sodium salt of cellulose succinate and 240 m of isopropyl alcohol were used.
1, 60 ml of water, 3.0 g of epichlorohydrin and 1 g of sodium hydroxide were put into a reaction vessel and mixed well, and then the reaction vessel was equipped with a reflux condenser and reacted at 60 ° C. for 6 hours. The obtained reaction product was sufficiently washed with methanol and then dried to obtain a crosslinked product of a sodium salt of cellulose succinate. The crosslinked product of the obtained sodium salt of cellulose succinate has a water absorption of a 0.9% aqueous sodium chloride solution of 121 g / g,
The degree of biodegradation is 86%, the water absorption of the electrolyte solution is high,
It had good biodegradability.

Comparative Example 1 Example 1 was repeated except that 7.1 g of monochloropropionic acid was used as the carboxylic acid for substitution of cellulose.
In the same manner as in the above, a crosslinked product of a sodium salt of cellulose propionate was obtained. The obtained crosslinked product of sodium salt of cellulose propionate had a water absorption of a 0.9% aqueous sodium chloride solution of 60 g / g and a biodegradability of 88%.

Example 2 Cellulose malonate was prepared in the same manner as in Example 1 except that 9.1 g of monochloromalonic acid was used as the polycarboxylic acid and 6.0 g of diglycidyl ethyl ether was used as the crosslinking agent. To obtain the sodium salt of
A crosslinked product of the sodium salt of cellulose malonate was obtained. The crosslinked product of the obtained sodium salt of cellulose malonate is
Water absorption of 0.9% sodium chloride aqueous solution is 113 g / g
In addition, the degree of biodegradation was 85%, the water absorption of the electrolyte solution was high, and the biodegradability was good.

Comparative Example 2 A crosslinked product of a sodium salt of cellulose acetate was obtained in the same manner as in Example 1, except that 6.2 g of monochloroacetic acid was used as the carboxylic acid for substitution of cellulose. The crosslinked product of the obtained sodium salt of cellulose acetate was 0.1%.
The water absorption of the 9% aqueous sodium chloride solution was 56 g / g, and the degree of biodegradation was 86%.

[0019]

According to the present invention, a cellulose derivative in which at least a part of hydroxyl groups of a glucose ring constituting cellulose is substituted by a polycarboxylic acid is used as a biodegradable water-absorbing material. It is possible to provide an extremely useful biodegradable water-absorbing material which has high biodegradability and is excellent in water absorption of an electrolyte solution.

Claims (4)

[Claims] 1. A cellulose polycarboxylate containing, as a part of a cellulose skeleton, a polycarboxylic acid glucose in which at least a part of hydroxyl groups of a glucose ring constituting cellulose is substituted by a polyvalent carboxylic acid. A water-absorbing material having biodegradability. 2. The biodegradable water-absorbing material according to claim 1, wherein at least a part of the carboxyl groups of the polyvalent carboxylic acid cellulose is an alkali metal salt. 3. The biodegradable water-absorbing material according to claim 1, wherein a part of the cellulose skeleton has a crosslinked structure. 4. A reaction between cellulose and a halogen-substituted polycarboxylic acid to produce a polycarboxylic acid cellulose containing glucose polycarboxylate as a part of the cellulose skeleton. A method for producing a biodegradable water-absorbing material, comprising reacting acid cellulose in the presence of a crosslinking agent.