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.