Morphology distribution and processing history of injection moulded polypropylenes

Abstract

The morphology distribution of injection moulded polypropylenes observed using optical microscopy and synchrotron X radiation is reported, the mouldings being performed under a range of conditions and with different grades of polypropylene. As has been observed before, a three-region multi-layer model is generally sufficient at first sight to describe the skin-core morphology of these injection-molded parts, with a surface skin, a spherulitic core and a transition shear layer. However the detail obtained using the high spatial resolution of the synchrotron X radiation reveals an underlying complexity. Samples were taken from PP plates at different distances from the end gate of the linear mouldings, and the X-ray data used to determine the distributions of crystallinity, β-phase concentration and the long spacing of crystallites. Different distributions are observed at different distances from the gate. The simulation software package Moldflow MPI, together with a simplified particle-tracking model is used to predict the thermal and shear histories of the polymer melt during the injection moulding process. The features of the layered structure and their dependence on the thermal and shear histories are discussed.