Crystallization of polypropylene near the surface in injection-molded plaques: A comparison of morphology and a numerical analysis

Skin morphology formation on injection-molded isotactic polypropylene (PP) was investigated using micro-beam synchrotron wide-angle X-ray diffraction and numerical simulation. The 1–20 μm depth range was characterized with an X-ray beam of 0.273 μm χ 0.389 μm in size. From an evaluation of doping nucleating agents (NA) in PP, the NAs did not work at a depth of 1 μm. α-specified NA affected crystallization within a 5-μm depth. β-specified PP showed α-form crystallinity at the 5–20 μm depth. The mesomorphic crystal near the surface showed extremely high orientation. From viscoelastic flow simulation, PP molecules near the surface were oriented in the flow direction by extensional flow in the flow front, but freezing occurred faster than flow-induced crystallization. It was estimated that the delay of crystallization occurred during the transient temperature. The deformation rate did not cause a difference in crystal morphology near the surface, but the cooling rate did. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.