Izod impact strength of polystyrene-based blends containing low molecular weight polybutadiene

Abstract

Experiments were conducted to determine the influence on impact strength of small amounts of low molecular weight polybutadiene pools dispersed within the glassy matrix of high impact polystyrene (HIPS)/polystyrene blends or acrylonitrile-butadiene-styrene (ABS)/polystyrene blends. The blends of HIPS and polystyrene or ABS and polystyrene were formulated to obtain materials containing small amounts of composite particles to act as craze initiators. Izod impact tests were conducted on standard single notched samples. The fracture surfaces of the Izod specimens and of double-notched tensile specimens were studied by means of scanning electron microscopy, and the internal morphologies of the blends were examined by transmission electron microscopy. Addition of low 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 were 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 strain rate is in the region of 10 −2s −1 at 20°C for the particular low molecular weight polybutadiene (3400 g mol −1, 74% 1,4 microstructure) employed here.