Processing Parameters-Cell Structure-Mechanical Properties Relationships In Microcellular Injection Molding

Compared with conventional injection molding, microcellular injection molding has many advantages, such as weight reduction, short molding cycle, low injection pressure and clamp force, and decreased part shrinkage. The properties of microcellular injection molded parts mainly depend on the cellular size and distribution. In this work, the microcellular injection molding of polystyrene (PS) and polypropylene (PP)/ethylene-propylene-diene monomer (EPDM) blends are investigated.Firstly, the different positions along the flow direction of microcellular injection molding PS samples exhibit different cellular size and density. The cells have smaller sizes and higher density far from the gate; the cell sizes are smaller near the gate; in the middle of simples, the cell sizes are larger.Secondly, the melt temperature and gas content have obvious effects on the cellular structure of the microcellular injection molded PP/EPDM blend samples. Lower melt temperature and weight reduction and higher gas content, back pressure, and injection speed can increase the cell density and reduce the cell size.Thirdly, the effects of processing parameters on the mechanical properties and shrinkage of the microcellular injection molded PP/EPDM blend samples are analyzd via orthogonal design. The results show that the most remarkable processing parameters for affecting the impact strength are the melt temperature and injection speed. Lower melt temperature and injection speed, as well as decreased gas content and back pressure, can improve the impact strength of the microcellular injection molded blend samples. Weight reduction is the most important fact for influencing the tensile strength of the microcellular injection molded blend samples. The shrinkage of the microcellular injection molded blend samples is much lower than that of the conventional injection molded blend samples, and is little affected by processing parameters.