RUBBER PARTICLE-SIZE AND CAVITATION PROCESS IN HIGH-IMPACT POLYSTYRENE BLENDS

The rubber particle size and its volume fraction are recognised as bei ng important factors in determining the yield and fracture behaviour o f high impact polystyrene (HIPS). However, correlations between the av erage particle size and cavitation in the rubber with toughening effic iency have only recently been established theoretically. This work pro vides further evidence on how the deformation kinetics in HIPS are aff ected by variations in the average rubber particle size highlighting a long the way the role of rubber cavitation in the process. Variations in the average particle size were achieved by melt blending different proportions of two commercial grades of HIPS that had the traditional multiple inclusion particle morphology. Tensile and impact properties of the blends were measured and correlated to morphological parameters determined by quantitative image analysis. It was found that yield an d fracture behaviour in tensile and impact test were strongly dependen t on the amount of sub-micron particles in the blend. At high rates, t oughness drops steeply with particle size. It was proposed that stress at yield and post yield strain hardening are controlled by particle s ize and rubber stretching respectively. Microfracture analysis by tran smission electron microscopy lent support to the arguments presented.