Structure Evolution upon Uniaxial Drawing Skin- and Core-Layers of Injection-Molded Isotactic Polypropylene by In Situ Synchrotron X-ray Scattering

The structure evolution of the oriented layer (skin) and unoriented layer (core) from injection-molded isotactic polypropylene samples upon uniaxial drawing is probed by in situ synchrotron X-ray scattering. The X-ray data analysis approach, called halo method, is used to semiquantitatively identify the transformation process of crystal phase upon uniaxial drawing. The results verify the validation of the stress-induced crystal fragmentation and recrystallization process in the deformation of the injection-molded samples under different temperatures. Furthermore, the end of strain softening region in the engineering stress-strain curves explicitly corresponds to the transition point from the stress-induced crystal fragmentation to recrystallization process. Basically, the skin and core layers of the injection-molded parts share the similar deformation mechanism as aforementioned. The stretching temperature which dramatically affects the relative strength between the entanglement-induced tie chains and the adjacent crystalline lamellae determines the crystal structural evolution upon drawing. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013,51, 1618-1631