(297d) Aspects of Foam Injection Molding a Thermoplastic Polyolefin with Chemical Blowing Agents

This work explores the effects of process conditions on different aspects of producing thermoplastic polyolefin (TPO) foam, examining the developed microstructure (i.e., size, density), surface quality, and the resulting mechanical properties of foam injection molded parts. Using a fractional factorial design of experiments (DOE) matrix, samples were injection molded by a shot-shot technique with two chemical blowing agents (CBA) at different concentrations, varying also shot sizes, melt temperatures, mold temperatures, back pressures, and injection speeds. The molded samples were analyzed for their foam microstructures (i.e., cell size, cell density and skin thickness), surface roughness, as well as mechanical properties (tensile and flexural moduli). It was observed that CBA concentration and melt temperature had important effects on foam microstructure. Increasing injection speed, shot size and mold temperature were helpful in improving the surface quality of foamed parts. The tensile and flexural moduli of TPO foamed parts were found greatly depend on the part density. The greater stiffness was seen at high levels of mold temperature, back pressure, shot size, melt temperature, injection speed, and at low concentration of endothermic CBA. Improvements in moduli were associated with well-developed cell microstructure. Appling our developed viscosity model in MoldFlow software for the flow of two-phase polymer/gas suspension, the simulated foam morphologies are to be compared with experimental data, hence the density of molded part will be obtained that could be used for the prediction of mechanical properties.