Plasticity of polystyrene -poly(2,6,dimethy1,1,4,phenylene oxide) blends

Abstract

The temperature and strain-rate dependence of the plastic yield in compression of blends between polystyrene (PS) and poly(2,6,dimethyl 1,4,phenylene oxide) (PPO) are investigated. The salient of our study is thhat an amount as small as 2 wt% of PPO can significantly lower the yield stress and elastic modulus of pure PS. This result is interpreted as being due to the creation of favourable nucleation sites for the onset of plastic deformation. The plastic flow stress, however, is unaffected by this small addition. When plotted at a constant T - T g our results show a nearly constant yield stress from 2% up to ca. 40 wt% PPO. At this point the yield stress starts to decrease and the activation volume increases, implying a more co-operative character of the plastic deformation mechanisms. This transition corresponds also to a change from more brittle to more ductile behaviour in tensile experiments.