Structure and mechanical properties of polystyrene foams made through microcellular injection molding via control mechanisms of gas counter pressure and mold temperature

In this study we developed a foaming control system using Gas Counter Pressure (GCP) combined with mold temperature control in the microcellular foaming (MuCell) process. The effects of the skin thickness, cell size, and cell morphology resulting from the three control mechanisms (including GCP control alone, mold temperature control alone, and GCP combined with mold temperature control) and process parameters on the mechanical properties of foamed polymer were investigated. In addition, the mechanical properties of foamed specimens molded from these three control mechanisms were also compared. It was found that skin thickness, cell size, and cell shape had significant influences on the mechanical properties of specimens depending on the molding conditions of gas counter pressure, holding time, and mold temperature. By increasing gas counter pressure, holding time, and decreasing the mold temperature, the tensile strength increased. In addition, by increasing gas counter pressure, holding time, and mold temperature alone, impact strength decreased. But, there were no clear relationships for processing parameters when GCP combined with dynamic mold temperature control was used because the effects of the skin thickness, cell size, and cell shape on the impact strength were unclear. Under experimental condition at mold temperature of 60 °C combined with appropriate GCP control system, better tensile strength and impact performance were achieved and specimens with thin skin, small and uniform cell size as well as better surface quality were produced.