A novel way to monitor the sequential destruction of parent-daughter crystals in isotactic polypropylene under uniaxial tension

The cross-hatched structural evolution of isotactic polypropylene (iPP) during uniaxial tensile deformation was investigated with in situ synchrotron radiation wide angle X-ray scattering. An effective way was developed to study parent and daughter lamellae separately with in situ environment. iPP sample was preoriented to generate a bimodal orientation of lamellae for distinguishing the parent and daughter lamellae, which will orient in orthogonal directions under flow-induced crystallization. The dumbbell samples were prepared along different angles with respect to preorientation direction to achieve multisided stretching. The structural evolution of parent and daughter lamellae was followed by recording the scattering from (110) crystallographic plane. It was observed that the parent lamellae were destroyed earlier than daughter ones, no matter which the tensile direction was. Mesophase was observed at very small strain of 0.3, immediately after the damage of cross-hatched structure, which may be attributed to the destruction of parent lamellae. Deformation induced mesophase was proved to be the small crystal cluster which was transformed from parent and daughter lamellae.