Fracture behaviour of polypropylene films at different temperatures: fractography and deformation mechanisms studied by SEM

The fracture surfaces and the deformation micro-mechanisms of one polypropylene homopolymer and three ethylene–propylene block copolymers (EPBC) have been studied by scanning electron microscopy. The results are compared to the essential work of fracture parameters obtained in a previous study with deeply double-edge-notched-tension samples of films fractured between −40 and 70 °C. The homopolymer shows shear-yielding at T≥−20 °C, but at lower T, crazing prevails. The EPBC display shear-yielding for T>0 °C, while a combination of cavitation and shear-yielding occurs at lower T, which is responsible for stress-whitening. The variations of the specific essential fracture work and specific plastic work with T and with ethylene content have been successfully explained in terms of the prevalent deformation mechanisms.