Comparison of isotactic and syndiotactic polypropylene as matrix materials of hybrid composites

Abstract

AbstractThe structure/property relationships and morphology of glass bead–reinforced syndiotactic and isotactic polypropylene composites containing 0 to 20 vol% thermoplastic elastomer (TPE) were studied. Polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS) and the corresponding block copolymer grafted with maleic anhydride (SEBS‐g‐MA) were used as the TPEs. The Young's modulus of hybrid composites based on s‐PP showed no dependence on the type of TPE used, whereas i‐PP hybrid composites containing SEBS had a higher Young's modulus than composites containing SEBS‐g‐MA. A comparison of the data with theoretical predictions of Young's modulus and tensile yield stress gave strong evidence of two different morphologies for the hybrid composites. The increasing tensile yield stress of s‐PP hybrid composites and i‐PP hybrid composites containing SEBS‐g‐MA was attributed to an interlayer formation and in‐situ encapsulation of glass beads, which resulted in core‐shell particles with improved interfacial interactions. In contrast, SEBS in hybrid composites based on i‐PP formed a separate dispersed phase. Crystallization and scanning electron microscopy studies also provided evidence of a core‐shell morphology for hybrid composites based on s‐PP. Results of lap‐shear and peel tests confirmed strong interfacial interaction between glass and SEBS‐g‐MA and between SEBS and s‐PP as well as i‐PP. Only above a critical volume fraction did the TPE provide significant improvement of the notched Izod impact strength of hybrid composites based on s‐PP or i‐PP.