Preparation of Microcellular Injection-Molded Foams Using Different Types of Low-Pressure Gases via a New Foam Injection Molding Technology

A new foam injection molding (FIM) machine was recently developed with a physical blowing agent directly delivered from its gas cylinder, while the supercritical fluid pumping unit is a must in the conventional FIM process. Herein, different types of gases including nitrogen (N2), helium (He), carbon dioxide (CO2), and argon (Ar) were used as the physical blowing agents for preparing polypropylene (PP) foams with a low pressure less than 5 MPa. It is revealed that CO2 and Ar endowed PP foams with higher cell densities, smaller cell sizes, and larger expansion ratios. In contrast, the poorest cellular structure was obtained for PP foams with He. Moreover, the effect of the gas type on mechanical properties of the resulting foams was investigated. Our findings demonstrated that the final cellular structures and mechanical performances of PP foams could be tailored by controlling the type of foaming agent, and this process could certainly be applied for other polymers.