JPS6017324B2 - Method for producing styrenic polymers with high water absorption and water retention properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a novel styrenic polymer that absorbs a large amount of water, swells, and retains water.

More specifically, the present invention relates to a method for producing a styrenic polymer having high water absorption and water retention properties using a sulfuric acid-treated product of an acrylonitrile-styrene copolymer or an alkali metal salt thereof. In recent years, various superabsorbent polymers based on synthetic and semi-synthetic polymers have been developed or put into practical use.

For example, polyacrylonitrile hydrolyzate, crosslinked polyethylene oxide, crosslinked carboxymethyl cellulose,
These include crosslinked polyvinyl alcohol, crosslinked hydroxyethyl methacrylate, and hydrolysates of starch-acrylic grafts. However, an inexpensive compound having a molecular structure like the styrenic polymer obtained in the present invention and having high water absorption and water retention properties has not yet been developed.
Already Hakama Kosho 49-46199 and Hakama Kosho 52-429
It is known that by hydrolyzing acrylonitrile in a single step, it is modified into acrylamide and/or acrylic acid or an acrylic acid metal salt, and a compound having hydrophilicity and water absorption properties can be obtained. On the other hand, sulfonated polystyrene, which is obtained by sulfonating polystyrene, has hydrophilicity and water-absorbing properties, as described in Honda Zato's book "Ion Exchange".

In addition, in Hakama Kosho 38-10343, a ternary copolymer resin of acrylonitrile-styrene-crosslinkable monomer (20 parts by weight or less of acrylonitrile monomer per 10 parts by weight of styrene monomer and crosslinkable monomer) A method is described for producing an ion exchange resin by sulfonating a composition containing a polymerized resin, but since it is a copolymer with a crosslinking monomer, it is highly crosslinked and has poor water absorption. This polymer has a low absorbency and is intended for the production of ion-exchange resins, and is essentially different from the high-absorbency polymer targeted by the present invention.

The present inventors used a polymer of acrylonitrile and styrene as a starting material, and treated it with sulfuric acid to simultaneously hydrolyze and sulfonate, respectively.
The present invention was achieved by discovering that a styrenic polymer having a novel molecular structure, low cost, and highly water-absorbing and water-retaining properties can be obtained.

In the method of the present invention, when polyacrylonitrile or polystyrene itself is used as a starting material, the inter- and intra-molecular spaces are small and it is difficult to expect a high degree of water absorption, but by copolymerization, the inter- and intra-molecular spaces are widened. Therefore, a higher level of water absorption can be expected.

This is the rationale for using an acrylonitrile-styrene copolymer as a starting material. Therefore, a copolymer having a composition close to the azeotropic composition of acrylonitrile and styrene (25% by weight as acrylonitrile content), that is, an acrylonitrile-ru-styrene copolymer with an acrylonitrile content of 20 to 3% by weight, is used as the starting material for the present invention. A preferred copolymer. It should be noted that this acrylonitrile-styrene copolymer is used as a plastic that improves the disadvantages of polystyrene and has excellent properties such as transparency, heat resistance, hard plowing properties, impact resistance, and chemical resistance. It is well known.

For plastics, copolymer compositions with an acrylonitrile content of 20 to 3% by weight are commercially available in order to achieve the desired properties. Therefore, from the economic point of view, a copolymer having an acrylonitrile content of 20 to 30% by weight is preferable. In addition, the molecular weight of the starting material is a number average molecular weight of 5.
000 or higher satisfies the objectives of the present invention. 5000
When a copolymer resin having a number average molecular weight of less than This is because it is difficult to obtain elasticity and water retention.

Those commercially available for use in plastics have a number average molecular weight of about 50,00, and are preferable as starting materials for the present invention in terms of molecular weight. The acrylonitrile-styrene copolymer according to the present invention may be polymerized by any method such as bulk polymerization, emulsion polymerization, suspension polymerization, solution precipitation polymerization, etc. Polymers in a polymorphic form are preferred in terms of permeation of the reactant and swelling properties.

75-9% by weight of bamboo as a reaction treatment agent for sulfuric acid treatment
The object of the present invention can be obtained by using concentrated sulfuric acid at a concentration of . If the sulfuric acid concentration is less than 75% by weight, a product with a high degree of water absorption cannot be obtained. By treating with such concentrated sulfuric acid, it is possible to partially hydrolyze the acrylonitrile in the acrylolotritolystyrene copolymer and to partially sulfonate the styrene, resulting in a styrenic polymer having the desired high water absorbency. is generated. The conditions for the sulfuric acid treatment of the acrylonitrile styrene copolymer according to the present invention include a reaction temperature of 20 to 130 oo, a time of 0.5 to 3 hours, and a solid/liquid charging ratio (acrylonitrile styrene copolymer/concentrated sulfuric acid). ratio) is 1/5 to 1/40
(by changing the water absorption capacity arbitrarily within the range of 0.05 to 1.00%). Any high degree of water absorption can be set. If the reaction temperature is lower than 20°C, the reaction rate will be slow and it will be difficult to obtain a high level of water absorption.
If it is 3 pi or more, the acrylonitrile-styrene copolymer will easily dissolve in the reactant, and both are unfavorable.

Therefore, the reaction temperature is preferably 20 to 130 oo. The reaction time is 0. If the reaction time is less than 1 hour, the reaction will not be sufficient and a high degree of water absorption will not be obtained. Since the reaction proceeds sufficiently within 3 hours, the reaction time is preferably 0.5 to 3 hours. Regarding the solid/liquid charging ratio, if it exceeds 1/5, the reactant cannot sufficiently penetrate and swell to the center of the pearl-like or powder-like polymer and the reaction cannot be carried out, making it impossible to obtain a high level of water absorption. .

If it is less than 1/4 degree, the polymer will easily dissolve in the reactant,
It is difficult to carry out the permeation/swelling reaction which is a feature of the method of the present invention.

Therefore, the solid/liquid charging ratio is 1/5 to 1/40.
is preferred. Furthermore, if necessary, the sulfuric acid-treated product of the acrylonitrile-styrene copolymer obtained by the above reaction treatment is immersed in an aqueous solution of an alkali metal salt.
An alkali metal salt of an acrylonitrile-styrene copolymer treated with sulfuric acid can be obtained. The new styrenic copolymer obtained by the method of the present invention has high water absorption and water retention properties, and can be used in sanitary materials such as sanitary products and paper diapers, to prevent overwatering, and in areas with weak water retention capacity. Agricultural, forestry and horticultural materials used to improve water retention, dehydrating agents for organic substances such as solvents, fragrance preservatives for long-lasting indoor air fresheners, sealants, fire extinguishers, anti-condensation agents , suitable for use as an antistatic agent, etc.

The present invention will be described in detail below with reference to Examples. Example 1 Acrylonitrile 25% by weight, styrene 7 by suspension polymerization method
Beads with a copolymerization composition of 5% by weight and a number average molecular weight of 50,000 were produced.

After extracting the residual monomer with steam, 100 beads of 40-80 mesh were obtained using a vibrating sieve. The beads were poured into an aqueous solution of lk9 having a sulfuric acid concentration of 8 and a cloud weight of 8% in a glass beaker, and reacted for 1 hour at 8p. As time passed, the sulfuric acid was absorbed by the copolymer beads, causing them to swell and react, resulting in yellowed beads.
During this process, the beads increased in volume by about 1 inch. Next, the yellowed and reacted beads were mixed with a large amount of water to wash off unreacted sulfuric acid.

The volume further increased as the degree of cleaning increased. The hydrogel thus obtained was dried at 80:00 for 3 hours to obtain slightly yellowed dry beads. Infrared absorption spectrum analysis of these beads revealed that the absorption of the acrylonitrile group in 2220 Hada-1 decreased to a shoulder level, and absorption based on acrylamide and acrylic acid was observed in 1660 Arc-1 and 1710 Kite-1, respectively. ,
It was confirmed that acrylonitrile was hydrolyzed. In addition, absorption of sulfonic acid was observed between 1210 and 1010-1, and the production of sulfonated styrene was confirmed. The water-washed and swollen hydrogel was ion-exchanged with specified caustic soda and specified caustic potassium to convert it into a sodium salt type and a potassium salt type.

In this way, acid type, sodium type, and potassium type reactants were obtained. Examples 2 to 4 The same polymeric composition as in Example 1 was reacted under the chemical reaction conditions shown in Table 11 to obtain acid type reactants after washing and drying.

Examples 5 to 8 A copolymer composition containing 3% by weight of acrylonitrile and 70% by weight of styrene, with a number average molecular weight of 40,
000 beads were reacted in the same manner as in Examples 1 and 2 to 4 as shown in Table 1, and after washing and drying, an acid type reaction product was obtained.

Example 9 Treated product of Example 1 (sample numbers 1-1 to 1-3) 1 each
In the evening, PH = 1, pH = 7, boat = 4 water, 1% by weight saline, 3% by weight saline, 100 human urine soaked, 1
The saturated water absorption amount after standing for a period of time was measured.

The results obtained are shown in Table-2. From Table 2, it can be seen that the styrene polymer of the present invention is ionic and therefore is greatly affected by the ionicity of the liquid, but has a high degree of water absorption.

Example 100 The reactants of Examples 2 to 4 and 5 to 8 (sample numbers 2 to 8) were soaked for 1 night each in 300 minutes of water having a pH of 7, and the saturated absorption amount was measured after standing for 1 hour.

In addition, the saturated water-absorbed hydrogel was centrifuged at 200 pm for 1 minute to measure the amount of water removed, and the water retention capacity (water retention amount) was calculated. Table 3 shows the results obtained regarding water absorption and water retention. It can be seen from Taiichi 3 that the styrenic polymer of the present invention has high water absorption and water retention properties.

Comparative Example 10 Copolymer compositions similar to Examples 2 to 4 were reacted under the chemical reaction conditions shown in Table 1, and after washing and drying, an acid type reactant was obtained.

The water absorption and water retention properties of the obtained reaction product were measured by the method of Example 10. The results obtained are shown in Table 3. Comparative Example 2 Using suspension polymerization method, acrylonitrile 1% by weight, styrene 7%
Crosslinked beads having a number average molecular weight of 90,000 were prepared with a copolymerization composition of 0% by weight and 1% by weight of divinylbenzene.

These beads are reacted under chemical reaction conditions such as 0 in Table 1,
After washing and drying, an acid type reactant was obtained. The water absorption and water retention properties of the obtained reaction product were measured by the method of Example 10. The results obtained are shown in Table 3. Table 3 shows that because it has a crosslinked structure, its water absorption and water retention properties are very low. Table-1 Composition and reaction conditions of acrylonitrile-styrene copolymer Table-2 Composition and water absorption of absorption liquid (
evening/evening) Table-3 Water absorption and water retention (titer)

Claims (1)

[Claims] 1. An acrylonitrile-styrene copolymer with a number average molecular weight of 5000 or more and an acrylonitrile content of 20 to 30% by weight is treated with concentrated sulfuric acid at a concentration of 75 to 98%, and the obtained sulfuric acid treated product is treated with an alkali metal salt as necessary. A method for producing a styrenic polymer having high water absorption and water retention properties.