Scanning force microscopic investigation of plasticity and damage mechanisms in polypropylene spherulites under simple shear

Abstract

Plasticity and damage mechanisms have been investigated at the lamellar level by scanning force microscopy in bulk isotactic polypropylene under moderate applied shear stresses. The polypropylene under study contains both α and β spherulites. The SFM micrographs show clearly that the local mechanisms are basically the same for both α and β spherulites, but their intensity is much less lower in the α spherulites than in the β ones due to the presence of the daughter lamellae in the former case. The main deformation mechanisms which have been observed are: (i) kinking of the lamellae which lie along the principal compressive axis; (ii) nanocracks across the lamellae lying along the principal tensile axis; (iii) fragmentations of the lamellae which are parallel to the shear axis; (iv) fragmentations of the lamellae which are perpendicular to the shear axis.