| abstract |
@ A process for increasing the mechanical strength of a hydrogel is provided. An aqueous solution containing 6 wt% or more of polyvinyl alcohol having a degree of hydrolysis of not less than 95 mol% and an average polymerization degree of not less than 700 is subjected to a freezing step followed by a thawing step. Then, the mass thus obtained is further subjected to at least one additional cyclic processing step including the freezing and thawing steps. The product hydrogel is hard or not too soft and not swollen in water. |