The rheological properties of weak gels of poly(vinyl alcohol) and sodium borate

Abstract The aim of this work was to establish whether the lifetime of the junction zones in the poly(vinyl alcohol)/borate gels depended on the chemical composition or concentration of the constituents. It was found that the maximum in the distribution of lifetimes was about 0.3 s and independent of the polymer, borate concentrations and of the degree of hydrolysis of the polymer. The gels changed their non-linear rheological behaviour with age, being strain softening when freshly prepared but strain hardening after a few days. This change in behaviour was attributed to a redistribution of borate ions with time.