Structure of the Hydrogels Obtained by Blending Polyvinyl alcohol) with Alginic Acid and Repeated Freezing and Thawing

Abstract

Rubbery hydrogels of high water content were prepared by blending of poly(vinyl alcohol) (PVA) with alginic acid followed by repeated freezing and thawing. The hydrogels swelled above pH 7, while shrinked below pH 7. There is a three dimentional honey-comb structure made by films or tapes in the hydrogel. In the film or the tape, PVA crystallites mainly form crosslinks in the hydrogels. A few -OH and -COOH groups of alginic acid molecules form hydrogen bonds with -OH goups of the amorphous PVA chains between crosslinked points. The swelling ratio decreases slightly with repeating immersions into an aqueous solution of pH>7, and then becomes an equilibrium value, because the alginic acid dissolves into water as a result of an increase in the dissociation degree of -COOH groups. © 1991, The Society of Polymer Science, Japan. All rights reserved.