Glass bead-reinforced isotactic polypropene hybrid composites containing 0–20 vol % thermoplastic elastomers were prepared to study both structure/property relationship and morphology development. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) and the corresponding block copolymer grafted with maleic anhydride (SEBS-g-MA) were used as thermoplastic elastomers. Hybrid composites containing SEBS gave higher Young's moduli than did those containing SEBS-g-MA. The experimental Young's moduli were in good agreement with the theoretical predictions according to Lewis and Nielsen. The lower moduli of hybrid composites containing SEBS-g-MA were attributed to interlayer formation and in situ encapsulation of glass beads, resulting in core–shell particles. This elastomeric interlayer impaired the filler reinforcement. Analysis of tensile yield stress and results of lap-shear tests confirmed strong filler–polymer interactions in composites containing SEBS-g-MA. Only in excess of a critical volume fraction did SEBS-g-MA afford a significant improvement of the notched Izod impact strength. In contrast to stiffness, Izod impact strength was not influenced by the type of elastomer and morphology. Investigation of crystallization and scanning electron microscopic studies proved the in situ encapsulation of the glass beads with SEBS-g-MA, whereas SEBS addition results in separately dispersed glass beads and SEBS microphases.
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Stricker et al. (1996) studied this question.