Effect of Biaxial Stretching Temperature and Gas Diffusion Expansion on Cellular Morphology of PP/CaCO3 and PP/talc Cellular Films

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 degrees C). Their corresponding cellular morphology was analyzed from scanning electron microscopy (SEM) micrographs. It was shown that film stretching at the lower temperature (152 degrees C) led to delamination of PP/CaCO3 or PP/talc interface, while it was not the case when these films were stretched at 158 degrees C. It was also observed that, when films were stretched at 152 degrees C, their corresponding developed cells had an average cell wall thickness t of around 3.6 mu m, an average cell height b of around 13.6 mu m, and an average cell aspect ratio a/b of around 5.6, where a (mu m) is the average cell width. These values were within the aimed cell geometrical specifications needed for cellular piezoelectric films.