Deformation behavior of oriented β-crystals in injection-molded isotactic polypropylene by in situ X-ray scattering

Peculiar oriented β-crystals with its c-axis perpendicular to the injection molding direction were formed in the injection molding processing. Simultaneous with the uniaxial elongation, in situ synchrotron X-ray scattering was employed to investigate the influence of oriented β-crystals on the deformation behavior of the skin and core layers of the injection-molded parts. The presence of oriented β-crystals accelerated the appearance of the yield point, and the yield point became the transition point from lamellar slip to fragmentation. Oriented β-crystals with more regular orientation in the skin layer were favorable for the earlier occurrence and delayed enlargement of microvoids. The formation of microvoids under loading turned out to be related with the separation or slip of oriented β-crystals, which is earlier than the destruction of β-crystals (β-α polymorphous transformation).