Structure and property of injection‐molded polypropylene along the flow direction

Abstract

AbstractThe structure and mechanical properties of injection‐molded polypropylene along the flow direction were investigated in this article. A remarkable difference was found in morphology and mechanical properties of the injection‐molded parts along the flow direction. The three‐layered structure (namely the skin, subskin, and core layer) showed a gradient distribution along the flow direction. The IR and WAXD results showed that the orientation of the subskin layer in the gate part is much higher than that in the far part. DSC analysis results indicated that the two parts (gate part and far part) of injection‐molded bar has the same degree of crystallinity that should not be responsible for the mechanical difference of the two parts. According to the measurement of residual internal stress, there is large difference between the gate part and far part, which is the main reason leading to the difference of impact behavior. The annealing treatment eliminated the internal stress, so the mechanical difference between the two parts decreased and the fracture type of the far part changed from brittle to ductile. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers