Injection processing and foaming behaviors of polypropylene composite foams

A volume-adjustable cavity of molding machine for polymer foaming was fabricated with renovation of an ordinary injection molding machine. Polypropylene (PP) composite foams were prepared by chemical foaming method via the volume-adjustable cavity of the molding machine. The decompressing and short shot processes in preparing the samples were carried out to adjust the cell structure of the foamed samples. The structures that foamed insufficiently, moderately, and excessively were observed in these two foaming processes. The foamed PP composite samples generated in decompressing process have more desirable cell structure than those generated by short shot process, specifically, the cell structure with the cell size of 46.97 μm, cell density of 3.18×10⁶ cell/cm³, and cell size dispersion of 10.76 μm was achieved in the decompressing process. A controlled foaming process was realized through the decompressing process using the injection foaming equipment with a volume-adjustable cavity. The foamed PP composite has the insufficient, moderate, and excessive foamed structures in these two foaming processes.