Cellular Polymers

In this work, the cellular morphology of polypropylene (PP)/calcium carbonate (CaCO₃) composite films was optimized with respect to piezoelectric cellular films criteria. To do this, a series of PP films filled with CaCO₃ micro-particles of three different particle sizes (3, 6 and 12 microns) were developed at various weight concentrations (3 to 44 wt. %). Before going through a gas diffusion expansion (GDE) step to inflate the initiated cells, all composite films were first produced via extrusion/calendaring then biaxially stretched to initiate the cellular structure by interfacial delamination between the CaCO₃ particles and PP matrix. After biaxial stretching and GDE, it was observed that only films with filler contents above 23 wt.% and 12 μm particle size presented a well-developed cellular structure. By optimizing the extrusion, biaxial stretching and GDE steps, we were able to generate a required cellular morphology where the average cell height ranged between 5 and 8 μm, which is considered good for further Corona charging. Also, the average cell aspect ratio (cell length divided by cell height) ranged between 4 and 10 with an average cell wall thickness between 7 and 12 μm, which is also considered as optimum for good piezoelectric properties.

In this article, the general-purpose polystyrene was reprocessed four times. The effect of repeated reprocessing of polystyrene on its polymeric properties and on its microcellular, foaming behaviour were investigated. It was observed that reprocessing leads to break of long polymeric chains into short chains, which resulted increment in PDI and MFI. Molecular weight and Glass transition temperature were found to decrease with increasing recycling stages. Reprocessing resulted abruptly decrement in viscosity of neat polystyrene. Effect of reprocessing on foaming behaviour was analysed properly in this report and it was found that reprocessing resulted in improvement in cell sizes and their distribution. A positive effect on expansion ratio was also observed during foaming of reprocessed specimens. Cell density was found to decrease with increasing recycling stages. The effect of saturation pressure and foaming temperature on microcellular foam morphology along with recycling were investigated. Effect of foaming time on cell size, cell size distribution, cell density, expansion ratio and cell wall thickness was investigated.