Microcellular Injection Molding Of PP/GF Composites

The polypropylene(PP)/glass fiber(GF) composites have been foamed by Mucell injection molding with supercritical nitrogen (ScN2) as a blowing agent. Cell structure, GF orientation and mechanical properties of two types of PP/GF composites in microcellular injection molding process were investigated. The results showed the cell morphology of injection samples from surface to core layer was definitely different due to cooling and shear effects. Sample mechanical properties can be effectively enhanced by improving the polymer chain orientation along the flow direction, optimizing cell structure, tightening the combination of PP and GF, and the orientation of the GF.The enhancement of PP(1684)/GF(950) composites was best when GF(950) content percentage is 11.82% which had excellent impact performance. The orthogonal experiment results showed that mechanical properties increases with the increasing shot size, but increases first then decreases with the increasing melt temperature, mold temperature, injection speed and SCF content. The order of various process parameters which influence on tensile and impact strength is:shot size>SCF content>injection speed>melt temperature>mold temperature, while that on bending strength is:shot size>melt temperature>SCF content>injection speed>mold temperature.The microcellular samples of PP(514F) and its composites with GF(508A) had good tensile and bending properties, with the best of 10.06% GF(508A) content. The two double-screw extruder granulation method is beneficial for GF to form a good orientation, and high speed mixer granulator prevents the degradation of PP material.