Morphologies and interfacial tensions of immiscible polypropylene/polystyrene blends modified with triblock copolymers

The morphology and the response to small amplitude oscillatory shear (SAOS) of polypropylene/polystyrene (PP/PS 90/10) blends compatibilized with styrene–butadiene–styrene (SBS) or styrene–ethylene/butylene–styrene (SEBS) triblock copolymer were studied in this work. The possibility of inferring the interfacial tension between PP and PS as a function of amount of triblock copolymer added to the blend using the morphological and rheological measurements was investigated. The concentration of compatibilizers ranged from 0 to 25% relative to the weight of the dispersed phase (PS). The addition of compatibilizers resulted in a reduction of the size of the dispersed phase particles following an emulsion curve. SBS was shown to form a third phase when added, at high concentrations, to the blend. The addition of compatibilizers to the PS phase resulted in a reduction of interfacial tension following an emulsion curve. It was shown that for both compatibilizers the concentration at which the interfacial tension essentially levels off is smaller than the concentration at which the average radius of the dispersed phase essentially levels off. The morphological, viscosity and interfacial tension results showed that SEBS is a better compatibilizer for the PP/PS blend than is SBS.