Effect of Biaxial Stretching Temperature and Gas Diffusion Expansion on Cellular Morphology of PP/CaCO 3 and PP/talc Cellular Films

Abstract

To evaluate the impact of the stretching temperature on the morphology of cellular polypropylene (PP) films, a series of PP films filled with spherical particles of calcium carbonate (CaCO₃) and platy talc particles with weight concentrations varying from 15 to 35 wt% were prepared by twin-screw extrusion then biaxially stretched at three temperatures (152, 155 and 158°C). Their corresponding cellular morphology was analyzed from scanning electron microscopy (SEM) micrographs. It was shown that film stretching at the lower temperature (152°C) led to delamination of PP/CaCO₃ or PP/talc interface, while it was not the case when these films were stretched at 158°C. It was also observed that, when films were stretched at 152°C, their corresponding developed cells had an average cell wall thickness t of around 3.6 μm, an average cell height b of around 13.6 μm, and an average cell aspect ratio a/b of around 5.6, where a (mm) is the average cell width. These values were within the aimed cell geometrical specifications needed for cellular piezoelectric films.