PLASTICITY OF POLYSTYRENE-POLY(2,6,DIMETHYL,1,4,PHENYLENE OXIDE) BLENDS

The temperature and strain-rate dependence of the plastic yield in com pression of blends between polystyrene (PS) and poly(2,6,dimethyl 1,4, phenylene oxide) (PPO) are investigated. The salient result of our stu dy is that an amount as small as 2 wt% of PPO can significantly lower the yield stress and elastic modulus of pure PS. This result is interp reted as being due to the creation of favourable nucleation sites for the onset of plastic deformation. The plastic how 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 w t% PPO. At this point the yield stress starts to decrease and the acti vation 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 experim ents. (C) 1998 Elsevier Science Ltd. All rights reserved.