HIGHLY WATER-ABSORBING SUBSTANCE BASED ON STARCH AND POLYACRYLONITRILE, AND ITS PREPARATION

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.