The effects of shear on interfacial morphology evolution of over-injection molded polypropylene were investigated in this article. The interfacial morphologies at different distance from the gate under different shear effects

induced by different injection pressure and injection speed

was observed by polarized light microscopy (PLM) and differential scanning calorimetry (DSC) . It was found that injection pressure played more predominant role in the interfacial morphology development than injection speed. The PLM results also showed that less transcrystal was found at the interface due to high injection pressure

indicating that enhanced molecular orientation by increasing injection pressure was unfavorable for the crystallization at the interface during over-injection molding. The interfacial morphology can be controlled by changing injection pressure and injection speed.