Fracture propagation in particulate filled polypropylene composites

Abstract

Isotactic polypropylene (PP) composites with 40% (by weight) of different fillers, such as talc, CaCO₃ and mica (325 and 1000 mesh sizes) were prepared by injection moulding. In the case of PP-mica composites, scanning electron micrographs of the polished sections revealed that flakes are oriented in the skin areas parallel to the mould surface and in the interior there is a flake distribution more perpendicular to that. The notched specimens of PP and all its composites under study were fractured at −30, 25 and 80° C. Virgin PP exhibited brittle failure at −30 and 25° C with comparatively higher values of fracture toughness (K _c), and gross yielding leading to crack-blunting took place at 80° C. The fracture toughness of neat matrix and its composites were correlated with microstructural parameters. Incorporation of CaCo₃ avoided the catastrophic failure of PP at −30° C while any of the fillers could avoid brittle failure at 25° C. Failure mechanisms were observed by scanning electron microscopy of the fractured surfaces. The performance of PP was significantly affected by the incorporation of fillers.