Microcellular foaming of polypropylene containing low glass transition rubber particles in an injection molding process

Microcellular foams in polypropylene containing rubber particles were produced in an injection molding process. The foams are generated because of the thermodynamic instability and are controlled by formation process. The effect of processing parameters on microcellular foaming was investigated in the injection molding process. Injection speed and pressure are less important factors but packing pressure plays an important role in controlling the foam density. A critical packing pressure, about 5 × 10⁶ Pa, was found to generate microcellular foams in our polypropylene material system. Rubber particles inside the polypropylene seem to stabilize the microcellular foams.