Experiment and simulation of foaming injection molding of polypropylene/nano-calcium carbonate composites by supercritical carbon dioxide

Microcellular injection molding of neat isotactic polypropylene (iPP) and isotactic polypropylene/nano-calcium carbonate composites (iPP/nano-CaCO₃) was performed using supercritical carbon dioxide as the physical blowing agent. The influences of filler content and operating conditions on microstructure morphology of iPP and iPP/nano-CaCO₃ microcellular samples were studied systematically. The results showed the bubble size of the microcellular samples could be effectively decreased while the cell density increased for iPP/nano-CaCO₃ composites, especially at high CO₂ concentration and back pressure, low mold temperature and injection speed, and high filler content. Then Moldex 3D was applied to simulate the microcellular injection molding process, with the application of the measured ScCO₂ solubility and diffusion data for iPP and iPP/nano-CaCO₃ composites respectively. For neat iPP, the simulated bubble size and density distribution in the center section of tensile bars showed a good agreement with the experimental values. However, for iPP/nano-CaCO₃ composites, the correction factor for nucleation activation energy F and the pre-exponential factor of nucleation rate f₀ were obtained by nonlinear regression on the experimental bubble size and density distribution. The parameters F and f₀ can be used to predict the microcellular injection molding process for iPP/nano-CaCO₃ composites by Moldex 3D.