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.