EFFECTS OF RADIATION ON MECHANICAL-PROPERTIES OF POLYBUTADIENE POLYSTYRENE BLENDS/

Blends containing 3 wt % low molecular weight polybutadiene (PB) in a polystyrene (PS) matrix were prepared via a precipitation technique th at yielded spherical, submicron pools of PB. Tensile specimens made fr om these blends were then irradiated with high energy electrons in air at dose levels from 0 to 70 Mrads. The blends, which previously showe d high levels of toughness approaching that of high impact PS, lost al l enhanced toughness when irradiated above 10 Mrads. Analysis of pure PS specimens irradiated over the dose range from 0 to 45 Mrads showed no appreciable dependence of mechanical behavior on dose level. Molecu lar weight studies of the polybutadiene demonstrated only a very modes t increase in molecular weight in the dose range studied here; therefo re, reduced mobility of the PB in the blends was not the reason for th e dramatic drop in toughness with radiation dose. It was concluded tha t radiation-induced scission of the PS near the surface of the blends resulted in a significant local reduction in molecular weight. This de graded layer led to premature craze failure and hence a low level of t oughness. It was demonstrated that the absence of oxygen during the ir radiation process or the removal of the scissioned surface layer via m echanical abrasion resulted in a recovery of toughness. (C) 1995 John Wiley & Sons, Inc.