Effect of cross-linking agents on the dynamic mechanical properties of hydrogel blends of poly(acrylic acid)-poly(vinyl alcohol-vinyl acetate).

A range of hydrogels were prepared by blending aqueous solutions of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) in various proportions. The effects of two cross-linking agents (glyoxal and glutaraldehyde) and subsequent thermal treatment on the properties of the blends are discussed. Dynamic mechanical analysis (DMA) of the xerogels indicated complete miscibility of the various blends which was evident from the appearance of a single glass transition temperature (Tg) in the presence of either glyoxal or glutaraldehyde at all thermal treatments studied. A 50/50% wt/wt blend was found to have the highest storage modulus and was thus selected for further study. Hydrogels prepared with glutaraldehyde without subsequent thermal treatment exhibited higher storage modulus values than those prepared using glyoxal when tested isothermally at 20 degrees C in a water bath. A further increase in the storage modulus was observed when these hydrogels were thermally treated at 120 or 150 degrees C. In a non-isothermal study on the cross-linked hydrogels, no variation in storage modulus was observed. Broad peaks were observed in tan delta plots, these peaks shifting towards higher frequencies as the degree of cross-linking increased in the hydrogel.