IZOD IMPACT STRENGTH OF POLYSTYRENE-BASED BLENDS CONTAINING LOW-MOLECULAR-WEIGHT POLYBUTADIENE

Experiments were conducted to determine the influence on impact streng th of small amounts of low molecular weight polybutadiene pools disper sed within the glassy matrix of high impact polystyrene (HIPS)/polysty rene blends or acrylonitrile-butadiene-styrene (ABS)/polystyrene blend s. The blends of HIPS and polystyrene or ABS and polystyrene were form ulated to obtain materials containing small amounts of composite parti cles to act as craze initiators. Izod impact tests were conducted on s tandard single notched samples. The fracture surfaces of the Izod spec imens and of double-notched tensile specimens were studied by means of scanning electron microscopy, and the internal morphologies of the bl ends were examined by transmission electron microscopy. Addition of lo w molecular weight polybutadiene does not increase the impact strength of the blends because, at the high strain rates of the Izod test, the low molecular weight polybutadiene loses its effectiveness as a local plasticizer of craze fibrils. Tensile tests at various strain rates w ere conducted in order to estimate the strain rate where the mobility of the low molecular weight polybutadiene cannot keep up with the rate of craze propagation through the polystyrene matrix; this critical st rain rate is in the region of 10(-2) s-1 at 20-degrees-C for the parti cular low molecular weight polybutadiene (3400 g mol-1, 74% 1,4 micros tructure) employed here.