Polystyrene Foam with High Cell Density and Small Cell Size by Compression-Injection Molding and Core Back Foaming Technique: Evolution of Cells in Cavity

Many efforts have been made to obtain uniform cell structures from foam injection molding techniques. However, cell nucleation mechanism and complex dynamics during the cell formation have rarely been well understood. Here, high-pressure foam injection molding (HPFIM) is achieved by combining the injection-compression molding with core back foaming (ICMCBF) technique. The influences of compression pressure and time on the cell structure of polystyrene foam during the foaming process are studied. Compared with low pressure for conventional foam injection molding, high compression pressure (200bar) and fast pressure drop rate of ICMCBF endow the foam with the highest cell density (1.59x10(7)cells cm(-3)), and the smallest cell size (15 mu m). The tensile strength and impact strength are enhanced by about 60% (from 22.3 to 35.6MPa) and 80% (from 3.6 to 6.8MPa), respectively. This study gives a critical understanding of the cell nucleation and growth mechanism of the foam injection molding and supplies a new strategy for the fabrication of foam with uniform cell structure.