EFFECTS OF SORBED WATER ON PROPERTIES OF LOW AND HIGH MOLECULAR-WEIGHT PMMA .1. DEFORMATION AND FRACTURE-BEHAVIOR

The influence of sorbed water on deformation and fracture behavior of both low and high molecular weight poly(methylmethacrylate) has been investigated. In the low molecular weight polymer, addition of water produces a rise in internal friction in the minus 100 degree C region but it has no apparent effect on the beta -relaxation process. The tensile strength falls gradually with increasing concentration of water and more rapidly at high concentrations. Observed deformation modes include shear bands, crazes, and diamond-shape surface cavities. However, water saturated samples fail in a brittle manner. From the observed deformation behavior, as well as from observation of fracture surface morphology, it is suggested that sorbed water acts as a mild plasticizer for PMMA up to a concentration of about 1. 1% and, at higher water concentration, water clustering occurs.