Effects of sorbed water on properties of low and high molecular weight PMMA: 1. Deformation and fracture behaviour

Abstract

The influence of sorbed water on deformation and fracture behaviour 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 −100°C region but it has no apparent effect on the β-relaxation process. The tensile strength falls gradually with increasing concentration of water and more rapidly at high concentrations. Ductility initially increases with increasing water content but it reduces at high concentration. In the high molecular weight polymer, in contrast to the low molecular weight material, a yield maximum is observed for both dry and air-equilibrated samples of low moisture content and some samples show both necking and cold drawing prior to fracture. 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 behaviour, 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.