Thermal and rheological properties of poly(vinyl alcohol) gel with boric acid as a crosslinking agent

The gel of poly(vinyl alcohol) polymer with boric acid, added as a crosslinking agent, was made with a mixture of dimethyl sulfoxide and water. The thermal and dynamic modulus properties of poly(vinyl alcohol) gel were measured by a differential scanning calorimeter and a dynamic mechanical thermoanalyst. Results show that an increase of poly(vinyl alcohol) polymer or boric acid content to the gel makes an increasing of gel to sol transition temperature, endothermic enthalpy, and dynamic modulus. The maximum value of gel to sol transition temperature, endothermic enthalpy, and dynamic modulus happened at the volume ratio of 6 : 4 of dimethyl sulfoxide to water, which is independent on the poly(vinyl alcohol) and the boric acid content. According to the modified Eldridge-Ferry theory for thermoreversible gel, it is found that both the gel to sol transition temperature and the endothermic enthalpy versus poly(vinyl alcohol) content could be superimposed with respect to the boric acid content. (C) 1999 John Wiley & Sons, Inc.