JPS63193910A - Production of water absorbing starch - Google Patents

Abstract

PURPOSE:To efficiently obtain a water absorbing starch, having excellent water absorptivity and useful as napkins for absorbing menstrual blood, etc., in a short process, by simultaneously polymerizing and drying a hydrophilic polymer mixture solution of a starch graft copolymer having alkaline functional graft chains as a raw material. CONSTITUTION:A basic aqueous solution is reacted with a starch graft copolymer obtained by graft polymerizing an alkaline functional monomer onto starch, preferably at 1:0.1-1:6 weight ratio to introduce hydrophilic groups. An ethylenically unsaturated acid in an amount of 1.0-2.0mol. (based on the number of mol. of the residual alkali) is reacted with a basic substance remaining in the resultant aqueous solution containing the hydrophilic polymer to neutralize the polymer. A polymerization initiator in an amount of 0.1-10.0wt.% (based on the ethylenically unsaturated acid) is then added, simultaneously polymerized and dried at 100-200 deg.C to afford the aimed water absorbing starch utilizable as a water holding agent for potted plants, water stop agent for civil engineering work, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing water-absorbing starch using a starch graft copolymer having an alkali-functional graft chain as a raw material.

The water-absorbing starch according to the present invention can be used in dry starch or film form as an adjuvant to improve the performance of napkins for menstrual blood absorption, tampons, diapers for urine absorption, bed bats, etc., and also for potted plants. It can be used for applications such as water retention agents for industrial use and water stop agents for civil engineering works.

(Prior art) Examples of super absorbent materials that can be used in the above applications include crosslinkable sodium polyacrylate, crosslinkable carboxymethyl cellulose, crosslinkable carboxymethyl starch, crosslinkable polyethylene oxide, and starch-polyacrylonitrile graft copolymers. Alkali saponified products of starch-polyacrylonitrile graft copolymers are known, and in particular, alkali saponified products of starch-polyacrylonitrile graft copolymers exhibit high water absorption and are highly practical substances.

This alkaline saponified product of starch-polyacrylonitrile graft copolymer is obtained by graft polymerization using 1.5 to 9 mol of acrylonitrile per 1 mol of starch in an aqueous medium using a ceric salt as an initiator, and then using an alkali base. It is obtained in powder form by saponification and has a gelling ability that absorbs 300 times more water (Japanese Patent Publication No. 14157/1983).

On the other hand, according to Japanese Patent Publication No. 54-14157, starch-
After saponifying the polyacrylonitrile graft copolymer with an alkali, the saponified product is heated to a pH of about 3 with an appropriate acid.
and precipitate a water-insoluble acidic starch-polyacrylonitrile copolymer saponified product, which is isolated and washed.
Again, it is disclosed that the water-absorbing agent is prepared by suspending it in water and readjusting the pH to about 4-12 by any suitable means, followed by drying.

(Problems to be Solved by the Invention) The reason why the above-mentioned complicated manufacturing process is required is because a large amount of basic substances are present in the solution of the saponified starch-polyacrylonitrile graft copolymer after saponification. This is because if the residue remains and is not removed, the quality of the final product, especially the water absorption capacity, will be significantly reduced.

After saponification, isolation and water washing are performed to remove remaining basic substances, but in this method, the starch-polyacrylonitrile graft copolymer saponified product in the water-insoluble acid type layer is exposed to a considerable amount of water. It exhibits swelling properties, absorbs a large amount of washing water and swells, and requires a large amount of fuel consumption to remove this water, making it unfavorable in terms of cost. Further, even if centrifugal dehydration or the like is performed, there is a problem in industrial production due to extremely poor filterability.

By further washing with water, water-insoluble acidic starch
Impurities remaining in the saponified polyacrylonitrile graft copolymer are removed, but at the same time, the graft copolymer itself is washed away during the process, and the yield usually decreases by about 10%. As a result, production efficiency is significantly reduced, and the graft polymer may also flow out into wastewater, causing environmental problems.

These problems occur not only when a starch-polyacrylonitrile graft copolymer is used as a raw material, but also in other starch graft copolymers having alkali-functional graft chains. .

(Means for Solving the Problems) As a result of intensive research in order to solve these problems, the present inventors applied a basic aqueous solution to a starch graft copolymer having an alkali-functional graft chain. After introducing a hydrophilic group into the graft copolymer, the basic substance remaining in the hydrophilic polymer-containing aqueous solution is neutralized with an ethylenically unsaturated acid, and a polymerization initiator is further added. The present inventors have discovered that the above-mentioned problems can be solved by producing water-absorbing starch by simultaneously polymerizing and drying a mixed solution containing a reactive polymer at a temperature of 100° C. or higher, and have completed the present invention.

Used in the present invention. Monomers that perform graft polymerization on starch are not limited to acrylonitrile, but include those with a functional group that can be hydrolyzed by a base and converted into a hydrophilic group, those with an amide group such as acrylamide and methacrylamide, Examples include heptamers having an ester group such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate.

The raw material is one or more of these seven starch particles graft-polymerized onto starch.

Preferred polymerization initiators when performing graft polymerization on starch are:
Other preferred initiators may also be used by those skilled in the art, including but not limited to the ceric ammonium nitrate-nitric acid system.

The weight ratio of starch and alkali-functional additive is 1:0.1.
Graft polymerization is preferably carried out at a ratio of ~1:6.

The type of starch used in the present invention is not particularly limited, and includes general starches such as wheat starch, corn starch, potato starch, tapioca starch, and sweet potato starch, as well as etherified starch, esterified starch, crosslinked starch, and oxidized starch. Modified starches such as starch, acid-treated starch, dextrin, pregelatinized starch, etc. may also be used, and when used, it is preferable to humidify with water and swell sufficiently or use in the form of gelatin before graft copolymerization.

The starch graft copolymer thus obtained is saponified with an alkali while heating in water or an aqueous solvent mainly composed of water. As the alkali to be used, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. are suitable, and the amount used is 1 mole of graft side chain monomer grafted to starch. ,0
．． 3 to 2.0 mol is preferred. If the amount of alkali used is lower than 0.3 mol, the time required for saponification becomes long and sufficient saponification cannot be carried out, resulting in a decrease in the water absorption capacity of the final product, which is undesirable. When the amount is 2 moles or more, although the saponification time is shortened, a large amount of alkali remains in the reaction system, and as a result, a large amount of ethylenically unsaturated acid is required, which is not preferable.

Saponification is suitably carried out at a temperature of 70 to 100°C for 1 to 5 hours.

After the saponification reaction, the ethylenically unsaturated acids that act on the remaining alkali include, but are not limited to, acrylic acid, methacrylic acid, itaconic acid, and styrene sulfonic acid. The amount of these ethylenically unsaturated acids is 1.0 per mole of remaining alkali.
~2.0 mol is preferred. If it is less than 1.0 mol, sufficient neutralization will not be achieved and the basic substance will remain, which is not preferable. Moreover, if it exceeds 2.0 moles, it is not preferable because the pH of the water-absorbing agent becomes low and the rinsing water-absorbing ability decreases.

The initiator added after saponification may be one commonly used, such as potassium persulfate, ammonium persulfate, hydrogen peroxide,
Examples include t-butyl peroxide. The amount added is preferably 0.1 to 10.0% by weight based on the ethylenically unsaturated acid. Polymerization and drying of the mixture thus obtained are as follows:
It is carried out simultaneously on the surface of at least one roller at a temperature of 100-200°C.

(Function) The water-absorbing agent obtained by the present invention can be produced in a much shorter process than conventional methods, has extremely high production efficiency, and has a high water-absorbing capacity that is almost the same as that of conventional products. are doing. Taking advantage of this property, it is used in napkins for absorbing menstrual blood, tampons, diapers for absorbing urine, sweat absorbents, bed bats, etc.

(Examples and Effects) Examples 1 to 5 25 g (dry weight) of cornstarch was suspended in 400 mQ of water, heated to 75°C, maintained at this temperature for 30 minutes, and then cooled to 30"C. The indicated amount of monomer was added and stirred for 30 minutes, 15 g of IN cerium ammonium nitrate nitric acid solution was added, and the reaction was carried out by stirring at 35°C for 3 hours.The starch graft copolymer was separated and purified by filtration, and after drying. Table 1 shows the grafting ratio.

Table 1 1): AN represents acrylonitrile 2): EA represents ethyl acrylate Examples 6 to 10 The starch graft copolymers obtained in Examples 1 to 5 were each suspended in water, and 13.0% % slurry liquid. Example 6 uses what was obtained in Example 1, and Example 7.
No. 8, 9.10 used those obtained in Examples 2.3 and 4.5, respectively. A predetermined amount of alkali shown in Table 2 was added to this, saponification was performed at 90° C. for 2 hours, and then cooled to room temperature.

Thereafter, it was neutralized with the ethylenically unsaturated acid shown in the table.

Table 2 The amount required for neutralization is shown in Table 3, and the type and amount of initiator are also shown in Table 3.
Shown below. These materials were directly fed to a double drum dryer with a surface temperature of 138 to 145°C to obtain a pale yellow brittle film. Table 4 shows the amount of water absorbed and the amount of residual water.
It was shown to.

Table 3 As a comparative example, the water absorption rate and residual alkali amount of the products obtained by simply saponifying the products obtained in Examples 1 to 5 with alkali are shown and compared with the examples. It is better to add numerical values for the amount of residual alkali to the examples.

Comparative Examples 1 to 5 Table 5 shows the water absorption amount and residual alkali amount when Examples 6 to 1o were not neutralized with ethylenically unsaturated acid and were dried with a drum dryer as they were after saponification.

Table 5

Claims (1)

[Claims] After introducing a hydrophilic group into the graft copolymer by acting a basic aqueous solution on the starch graft copolymer having an alkali-functional graft chain, an ethylenically unsaturated acid is added to the aqueous solution containing the hydrophilic polymer. A water-absorbing starch is produced by simultaneously polymerizing and drying the hydrophilic polymer mixed solution obtained by acting on the remaining basic substance to neutralize it and further adding a polymerization initiator at a temperature of 100°C or higher. Manufacturing method.