THE RHEOLOGICAL PROPERTIES OF WEAK GELS OF POLY(VINYL ALCOHOL) AND SODIUM-BORATE

The aim of this work was to establish whether the lifetime of the junc tion zones in the poly(vinyl alcohol)/borate gels depended on the chem ical composition or concentration of the constituents. It was found th at the maximum in the distribution of lifetimes was about 0.3 s and in dependent of the polymer, berate concentrations and of the degree of h ydrolysis of the polymer. The gels changed their non-linear rheologica l behaviour with age, being strain softening when freshly prepared but strain hardening after a few days. This change in behaviour was attri buted to a redistribution of berate ions with time. (C) 1997 Elsevier Science Ltd.