Mechanical and wear properties of poly(vinyl alcohol) hydrogels

Poly(vinyl alcohol)(PVA) hydrogels with low water contents were prepared by low temperature crystallization of PVA solution from a dimethyl sulfoxide/H2O mixed solvent, followed by high-temperature annealing after drying and the subsequent re-swelling with water. The tensile strength and dynamic modulus of PVA hydrogels increased upon annealing, irrespective of the degree of polymerization (DP) of PVA, but always at the sacrifice of the water content of hydrogel. In addition to the mechanical strength, the hardness of PVA hydrogels was improved by lowering the water content. The highest tensile strength(20 MPa) and the highest dynamic modulus(l80 MPa) were obtained when hydrogel was prepared from PVA with DP of 11000 and annealed at 140 degrees C for 24 h. The wear resistance strongly depended on the mechanical strength and coefficient of friction of PVA hydrogels. The wear volume of the hydrogel prepared from PVA with DP of 8800 decreased with the decreasing coefficient of friction and the increasing mechanical strength of PVA hydrogel except for the 25 wt% PVA hydrogel at 2.5 MPa. Furthermore, any wear particles were not detected for the 45 wt% PVA hydrogel at 2.5 MPa and the 25 wt% PVA hydrogel at 2.0 and 2.5 MPa.