Rheological properties and morphology of PP/PS polymer blends

The influence of the addition of styrene-butadiene-styrene (SBS) or styrene-ethylene/butylene-styrene (SEBS) block co-polymers on the morphology and rheological behavior of PP/PS (90/10) blends was studied. Morphology was studied using scanning electron microscopy (SEM). The rheological behavior was studied using small amplitude oscillatory shear measurements. It was shown that the size of the dispersed phase decreased when SBS or SEBS was added to the blend, following an emulsion curve. The decrease of the size of the dispersed phase was larger when compatibilizing with SEBS than with SBS, suggesting SEBS to be the better choice when compatibilizing PP/PS blends. The interfacial tension between PP and PS was determined using rheological measurements, and was found to be 6.23 dynes/cm at 200 °C, which correlated well to the value obtained by the pendant drop method.