Mechanical properties and fractal morphology of high-impact polystyrene/poly(styrene-b-butadiene-b-styrene) blends

Blends of high-impact polystyrene (HIPS) and polystyrene-b-polybutadiene-b-polystyrene block copolymers (SBS) (thermoplastic elastomers, Kraton D1101) have been studied with recycling in view. Binary HIPS/SBS elastomer systems containing up to 85% of SBS elastomer were investigated. The blends were characterized by measuring dynamic mechanical properties, creep and recovery, and by defining morphology. The heterogeneous blends exhibit a two-phase morphology. This structure is investigated by scanning electron microscopy (SEM) and compared to mechanical and processing properties as a function of SBS content. Increasing the SBS content one observes a vanishing PS-related brittle type of fracture, while an SBS-related ductile fracture emerges. Best mechanical properties are obtained for HIPS/SBS 90/10 blends. The topographical images of polymer blend fracture surfaces were processed using fractal analysis software to obtain the fractal indices of the surfaces. The average (classical) fractal index was less than two for the fracture surfaces of styrenic blends (HIPS/SBS). These fractal results were correlated with the blend mechanical properties and with the Hurst roughness exponent, obtained from the time series of processing parameters (torque, melt pressure). Hence, it is considered that the processing and mechanical results are in good agreement with the fractal properties of the fracture surfaces even for heterogeneous polymer blend materials.