Influence of Processing Conditions on the Morphological Structure and Ductility of Water-Foamed Injection Molded PP/LDPE Blended Parts

Water-foamed injection molding (WFIM) uses conventional injection molding (CIM) with water as a physical foaming agent. Compared to CIM, WFIM is a much more complicated process. As such, it is critical to determine the processing conditions for fabricating quality parts using WFIM. We used the design of experiment (DOE) method based on the Taguchi method to determine the influence of the processing conditions on the morphological structure and ductility of PP/LDPE WFIM parts, which were investigated by tensile testing and scanning electron microscopy (SEM). Our research suggests that fabricating PP/LDPE super-ductile parts using WFIM is indeed feasible. Our research also indicates that there is a close relationship between the ductility and the foamed structures, both of which are deeply influenced by the processing conditions. The analysis of variance results shows further that the water content had the greatest influence on the ductility, followed by the melt temperature, packing time, packing pressure, and PP/LDPE ratio. However, the ductility was only slightly influenced by the mold temperature, injection pressure, and injection time in WFIM. As to the number of cells, the order of influence was melt temperature, water content, packing time, packing pressure, mold temperature, injection pressure, PP/LDPE ratio, and injection time, in that order. In addition, applying DOE is a quite effective method for deducing the optimal set of effective factors in WFIM to produce super-ductile parts with a maximum number of cells. To our knowledge, this is the first time that the relationship among the processing conditions, ductility, and foamed structure of PP/LDPE WFIM super-ductile parts has been investigated and reported.