Insight into unique deformation behavior of oriented isotactic polypropylene with branched shish-kebabs

Branched shish-kebabs (bimodal orientation of lamellae) were successfully fabricated in oriented isotactic polypropylene (iPP) by a strong shear flow provided by a modified injection molding (OSIM) technique. Simultaneous with the uniaxial tensile, the deformation behavior of this unique branched shish-kebabs was probed by in situ synchrotron X-ray scattering. Compared with the isotropic counterpart, branched shish-kebabs exhibited enhanced strength and modulus without obvious necking. During deformation, the initial separation of kebabs drove the rotation of branched lamellae towards the tensile direction with constant distance herein, which turned out to be an auxetic behavior. Subsequently, partial destruction of branched lamellae and significant lamellae slip of kebabs occurred, followed by reordering of kebabs and the residual branched lamellae accompanying the formation of new crystals with their c-axis along the tensile direction. On the whole, this work testified the validation of 'stress-induced crystal fragmentation and recrystallization process' principle in the deformation of oriented samples.