Effect of Processing Conditions on the Cellular Morphology of Polypropylene Foamed Films for Piezoelectric Applications

In this work, continuous extrusion-calendering was used to produce polypropylene (PP) foam films for piezoelectric applications. The setup is based on physical foaming using supercritical nitrogen (SC-N₂) and calcium carbonate (CaCO₃) as nucleating agent. In particular, the extrusion parameters (screw design, temperature profile, blowing agent and nucleating agent content) and post-extrusion conditions (calendaring temperature and speed) were optimized to achieve a specific stretched eye-like cellular structure with uniform cell size distribution. The morphology in both machine and transverse directions, as well as tensile properties were characterized. The results show that a cellular structure with a higher cell aspect ratio has a lower Young's modulus, which is appropriate for piezoelectric cellular films. Generally, the developed foam morphology presents high potential for the production of ferroelectret PP films used in different piezoelectric applications.