Morphology development of polypropylene cellular films for piezoelectric applications

In the present work, the dielectric nature of polypropylene and the softness of the cellular structure in the thickness direction of polypropylene cellular films were combined together to create a low cost and easily processable piezoelectric material. The effects of processing parameters, polymer crystallinity, filler type and concentration on the final structure of the cellular films were investigated. Three grades of calcium carbonate (CaCO3) filler having an average particle size of 0.7, 3 and 12 mu m were used. An optimized cellular film was developed by biaxial stretching and inflating a film made from three hot-pressed polypropylene sheets filled with 20 wt% of calcium carbonate particles with an average size of 12 mu m. The cells have an average length of 35 mu m and height of 4 mu m with a density ratio of 0.8. Its particle size distribution compares favorably with those available in open literature.