JPS6140341A - Highly water-absorbing substance based on starch and polyacrylonitrile, and its preparation - Google Patents

Abstract

PURPOSE:To prepare a highly water-absorbing substance having remarkably improved absorption of an aqueous solution containing salts, and water-absorption after the heat-treatment, easily, by saponifying a mixture of starch and polyacrylonitrile with an alkali. CONSTITUTION:The objective highly water-absorbing substance can be prepared by mixing (A) starch selected from natural starch (e.g. corn starch, potato starch, etc.), processed starch (e.g. etherified starch, esterified starch, etc.), starch-containing powder (e.g. corn grits, corn flour, etc.) and decomposed starch (having a polymerization degree of >=1) and (B) a polyacrylonitrile having a molecular weight of >=100,000, preferably >=300,000 and prepared by the polymerization of acrylonitrile in an aqueous solution preferably using a persulfate as a catalyst, and saponifying the mixture at an alkali concentration of 0.5- 7.5N, at 85-200 deg.C for 1-3hr. The weight ratio of A/B (solid basis) in the mixture is 0.2-10, preferably 0.3-4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method, and more particularly to a super absorbent material made of starch and polyacrylonitrile, and a method for producing the same.

[Industrial application field]

The so-called "highly absorbent material" absorbs several hundred times its own weight in water, and after absorbing the water, it turns into a jelly-like swollen glue, and this swollen glue has the unique property of not releasing water even when a small amount of pressure is applied. are doing. Therefore, it is widely used in many fields, such as sanitary napkins, disposable diapers, water retention agents for wet diapers, soil water retention agents for gardening, disposable kitchen wipes, medical absorbents, and water stop agents for civil engineering work. .

[Prior art]

Conventionally, such highly water-absorbing substances (substances) include
Carboxymethylcellulose, carboxymethylated starch, crosslinked polyethylene oxide, starch-polyacrylic acid graft copolymers and their crosslinked products, alkali saponified products of starch-polyacrylonitrile graft copolymers, and the like are known. In particular, water-absorbing materials based on 1-starch have the advantage of being relatively inexpensive and having a relatively high amount of water absorption.

[Problems to be solved by the present invention]

However, the superabsorbent materials according to the prior art described above have a) a high water absorption rate of approximately g 009/I in pure water, but in the presence of free ions such as o, q% physiological saline or artificial urine; b) Regarding the alkaline saponified product of starch-polyacrylonitrile graft copolymer (hereinafter abbreviated as H8PAN), the water absorption rate decreases significantly by heat treatment, that is, it becomes thermally stable. It had drawbacks such as poor performance.

By the way, regarding the above-mentioned drawback a), there have been methods of introducing sulfonic acid groups, sulfate groups, phosphoric acid groups, or phosphate groups into the monomers used, methods of crosslinking with formalin after alkaline saponification, and methods of crosslinking with formalin in the graft polymerization product. Methods of introducing xyl groups and the like have been proposed. However, none of the above methods was satisfactory as a solution to the above drawbacks &).

On the other hand, no method for solving the above drawback b) has been proposed so far.

The present invention improves or eliminates the drawbacks of &) l and b) above. That is, the object of the present invention is to provide a highly water-absorbent material that has significantly improved water absorption in an aqueous solution containing salts and water absorption after heat treatment compared to conventional products.

In addition, conventional superabsorbent materials cannot necessarily be manufactured using only simple and easy steps. For example, in the production of H8PAN, (a) starch is gelatinized to smooth the reaction before graft polymerization, and (b)
Use expensive initiators such as cerium salts for the graft polymerization reaction; (c) methanol to reduce viscosity;
This requires the use of an expensive organic solvent such as acetone (because the alkali saponified product of the graft copolymer exhibits high viscosity even at low concentrations).

Therefore, an object of the present invention is to provide a superabsorbent material which has excellent physical properties that eliminate the above-mentioned drawbacks a) and b), and which can be manufactured more easily than conventional products.

[Configuration of the present invention]

As a result of extensive research aimed at achieving the above object, the present inventors have discovered that a substance obtained by simply mixing starch and polyacrylonitrile and saponifying the mixture with an alkali has been found in a) above.
The present invention was completed by discovering that the drawbacks of (b) and (b) can be solved or improved.

That is, the seventh aspect of the present invention relates to a highly water-absorbent material produced by alkali saponification of a mixture of starch (4) and polyacrylonitrile (B).

Examples of the "starch" used in the present invention include natural starches such as cornstarch horse starch, wheat starch, horsetail starch, waxy cornstarch, monoamylose cornstarch, tapioca starch, and sago starch; etherified starch, esterified starch, Examples include modified starches such as cross-linked starch and oxidized starch; starch-containing powders containing proteins such as corn grits, corn flour, and wheat flour; in addition to these starches, processed cellulose such as carboxymethyl cellulose;
It may also contain polysaccharides such as guar gum and mannan.

Furthermore, "starch" in the present invention also includes starch-degrading proboscis, examples of which include glucose, oligosaccharides (maltose, maltotriose, maltotetraose, maltopentaose, etc.), cyclodextrin, and short-chain starch. In addition to xylose, amylodextrin, dextrin, amylose, dextran,! Examples include those having a degree of polymerization of 7 or more, such as luran.

"4-liacrylonitrile" in the present invention can be produced using acrylonitrile as a raw material by a conventionally known method, such as aqueous solution polymerization (Polymer Synthesis Experimental Method, pi4I'y, Tokyo Kagaku Dojin). As the polymerization catalyst, for example, benzoyl peroxide, azobisinbutyronitrile, ammonium persulfate, potassium persulfate, 77ium ammonium nitrate, ceric ammonium sulfate can be used, and in general, persulfates are used. is preferred.

The average molecular weight h of the polymer thus produced is 10
000 or more is preferable. Average molecular weight is 100
If it is less than 00, the amount of water absorbed by the resulting water-absorbing substance decreases, and it may become solubilized in water. Practically preferred average molecular weight is 100,000 or more, more preferably 300,000 or more.

Starch (A) and polyacrylonitrile (B) in the present invention
), the solid content weight ratio (A/B) of starch (A) to polyacrylonitrile (B) K is 0.2/
The range is preferably from / to 1071.

A/B is 0. : If it is less than 171, the superabsorbent material obtained may become water-soluble, requiring heat treatment at high temperatures, and the starch content in the material may be low, resulting in poor economic efficiency, etc. may become impractical. On the other hand, when A/B is larger than lo/l, the water absorption rate of the resulting super absorbent material tends to be low.

A highly preferable A/B range is from 0.37t to /l.

In the present invention, a mixture of starch and nitrile in polyacrylic is saponified with an alkali. Saponification with an alkali can be carried out by a conventional method. Specifically, for example, the alkali concentration is preferably in the range of about 0, A; , the time can preferably range from about 7 to 3 hours. The end point of saponification can be easily confirmed as the saponified product changes from reddish brown to pale yellow.

The obtained saponified product is neutralized or neutralized, separated and purified, and then spread on, for example, a Teflon plate and dried to obtain a film of the superabsorbent substance of the present invention.

The superabsorbent substance of the present invention may be in the form of a powder, in addition to the above-mentioned film form, if desired.

In short, its shape can vary depending on the end use.

The highly water-absorbent material of the present invention exhibits a high water absorption rate even for pure water and O, Tati physiological saline, as will be clearly seen in the examples described later, and can be easily formed into a film as shown in the above example. Therefore, it can be suitably used for disposable diapers, sanitary products, wet napkins, etc.

Furthermore, as shown in the examples described later, focusing on the feature of high water absorption after heat treatment, it can be effectively used as a water-absorbing material that requires heat molding, such as a water-absorbing thermoplastic material. You can clearly see what's going on.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example/ 200 parts of water was placed in a reactor equipped with a stirring bar, a nitrogen blowing tube, a thermometer, and a reflux condenser, and the mixture was stirred at 0°C for 30 minutes and replaced with nitrogen. To the reactor were added 22 parts of 7-crylotrile, 0.3 parts of potassium persulfate dissolved in 25 parts of water, and 0.3 parts of sodium bisulfite dissolved in 23 parts of water, and at 18. Polymerization was carried out for 3 hours.

The obtained polymer was passed through the mouth, washed with water, dehydrated and dried to obtain polyacrylonitrile having an average molecular weight of ゛/Iazoooo.

7 parts of the polyacrylonitrile and 1 part of glucose (i.e. A/B=///) are mixed uniformly, 20 parts of 017N sodium hydroxide aqueous solution is added, preheated in a hot water bath, and when it becomes reddish brown, it is heated in an oven at 700°C. It was saponified for 2 hours inside. After the saponification was completed, excess sodium hydroxide in the reaction solution was neutralized with glacial acetic acid, then methanol was added to precipitate the alkali saponified product, which was washed with methanol. After washing, disperse in water, concentrate and spread on a Teflon plate at 1.7jqC.
The mixture was dried under ventilation to obtain a film of an alkaline saponified mixture of glucose and polyacrylonitrile.

Example Six samples were subjected to the same operation as in Example 1 using maltose (degree of polymerization a) in place of cogelcose to obtain a film of an alkali saponified mixture of maltose and polyacrylonitrile.

Example 3 Short chain length amylose (average degree of polymerization, 2
The same operation as in Example 3 was performed except that 3) was used to obtain a film of an alkali saponified mixture of short-chain amylose and polyacrylonitrile.

Example t The same procedure as in Example 1 was carried out except that 11α-cyclodextrin (degree of polymerization 6) was used in place of glucose.
■■■ A film of an alkaline saponified mixture of α-cyclodextrin and polyacrylonitrile was obtained.

Example 5 Pullulan instead of glucose (average degree of polymerization/231)
) was carried out in the same manner as in Example 1, except that a film of an alkali saponified mixture of pullulan and polyacrylonitrile was obtained.

Example 6 Instead of 1 part of polyacrylonitrile and 1 part of glucose,
1 part polyacrylonitrile and 1.3 parts cornstarch (
That is, a film of an alkali saponified mixture of corn starch and polyacrylonitrile was obtained by carrying out the same operation as in Example 1 except that A/B=3//) was used.

Example The same operation as in Example 1 was carried out except that cornstarch was used instead of glucose, and a film t-i of an alkali saponified mixture of cornstarch and polyacrylonitrile was prepared.
Ta.

Example g Mixing ratio A/B of cornstarch and polyacrylonitrile
Perform the same operation as in Example 6 except that //3 is changed,
A film of an alkaline saponified mixture of corn starch and polyacrylonitrile was obtained.

Example 9 Oxidized starch (manufactured by Nihon Shokuhin Kako ■, M
A film of an alkali saponified mixture of oxidized starch and polyacrylonitrile was obtained by carrying out the same operation as in Example 1, except that Stooo) was used.

Example i.

A film of an alkali saponified mixture of corn flour and polyacrylonitrile was obtained by carrying out the same operation as in Example 1, except that corn flour was used instead of glucose.

Comparative Example: 10 parts of cornstarch and 1 core of water were heated in qAr under a nitrogen stream.
cc, and stirred for 3o minutes. After cooling to room temperature, 70 parts of acrylonitrile and ceric ammonium nitrate solution (/
Cerium ion in N nitric acid 001 mol/43) 4.
7 parts were added and graft polymerization was carried out at 25oC for 1 hour.

The reaction solution was dehydrated, washed with water, and dried to obtain a cornstarch-polyacrylonitrile graft copolymer.

Add 0 part of 0.7N aqueous sodium hydroxide solution to λ part of the corn starch polyacrylonitrile graft copolymer, preheat in a hot water bath, and when it becomes reddish brown, add 100 ml of
The mixture was baked in an oven for one hour. After saponification, excess sodium hydroxide in the reaction solution was neutralized with glacial acetic acid, methanol was added to precipitate a polymer, and the precipitate was washed with methanol. After washing, the mixture was dispersed in water, concentrated, spread on a Teflon plate, and dried with ventilation at 30°C to obtain a film of alkali saponified cornstarch graft copolymer.

Examples // (Measurement of water absorption rate) Film-like saponified alkali products of Examples 1 to IO and Comparative Examples were prepared at a concentration of about 0.0%. / l Accurately weigh, add 9 and 20 ONt of pure water or 0.9 normal saline to a roost beaker, and add 3
It was left for 0 minutes. Next, separate the water that has not been absorbed through the IrO mesh sieve, and remove the water from the bottom of the sieve using a tissue paper 4-
Excess water was removed.

The weight of the water-absorbing and swollen glue was measured, and the water absorption rate was determined in terms of ig/9 of the alkali saponified product using the following formula.

The results obtained are shown in Table 1.

Example / (Water absorption rate of heat-treated product) The alkali saponified films obtained in Examples 1 to 10 and Comparative Example were /3! ; The water absorption rate of pure water of the film obtained by heating under OC for 1 hour was measured in the same manner as in Example 1). The obtained measurement results are shown in Table 1, where C is the water absorption rate after heat treatment, D is the water absorption rate of the film without heat treatment, and the ratio (C/D) is shown as a percentage. [Effects of the Invention] The present invention The superabsorbent material obtained in the invention has the following advantages. (See Table 1)/) The water absorption rate of pure water is about 13 to 3 times that of conventional products, which is an excellent value.

e) 0.91 The water absorption rate of physiological saline is about 3 to 3 lower than that of conventional products.
- It improves the drawback a) described above.

3) The decrease in water absorption (pure water) due to heat treatment, as indicated by C/D, is much smaller than that of conventional products. That is, the water absorption rate after heat treatment decreases to about 10% for the conventional product, whereas the water absorption rate for the present invention shows a value of about 1IO to gos. In addition, the water absorption coefficient of the products of the present invention after heat treatment is extremely high at about SOO~ko1001/g, and some of them show a value about three times that of conventional products (Example DA). This sufficiently eliminates the drawback b).

Furthermore, the super absorbent material of the present invention can be produced by simply mixing starch and polyacrylonitrile and saponifying the mixture with an alkali, which is much simpler and easier to produce than conventional super absorbent materials based on graft copolymers, for example. It also has the advantage of being easy to manufacture.

Claims (6)

[Claims] (1) A highly water-absorbent material obtained by saponifying a mixture of starch (A) and polyacrylonitrile (B) with an alkali. (2) The superabsorbent material according to claim (1), wherein the starch is a member selected from the group consisting of natural starch, modified starch, starch-containing powder, and starch decomposition products. (3) The highly water-absorbent material according to claim (2), wherein the degree of polymerization of the starch decomposition product is 1 or more. (4) The average molecular weight of polyacrylonitrile is 10,000
The super absorbent material according to any one of claims (1) to (3), which is the above. (5) Solid content weight ratio (A/B) of starch (A) to polyacrylonitrile (B) in the mixture is 0.2/1 to 1
0/1, the super absorbent material according to any one of claims (1) to (4). (6) A method for producing a highly water-absorbent substance, which comprises mixing starch (A), polyacrylonitrile (B) and an alkali and saponifying the mixture.