Crystal phases, structure, and orientation in isotactic polypropylene after isothermal crystallization under oscillatory shear as a function of nucleation agent

2D wide-angle X-ray diffraction (2D-WAXD) measurement was performed to investigate the effects of both oscillatory shear and the nucleating agent on the crystalline structure distribution and orientation of isotactic polypropylene (iPP). 1,3:2,4-bis(p-methylbenzylidene) sorbitol (MDBS) and 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS) can induce alpha-PP and beta-PP simultaneously. The presence of MDBS (or DMDBS) and oscillatory strain (oscillatory frequency is fixed) exhibits a synergistic interaction on increasing the content of beta-crystals of iPP. Under the oscillatory shear field at the fixed oscillatory strain, the beta-crystal content and the orientation of iPP with and without MDBS (or DMDBS) change slightly with the increase of the oscillatory frequency. Comparing with MDBS (or DMDBS) nucleated iPP crystallization under shear field, the periodically changed flow direction of the oscillatory shear field leads to the shorter alpha-row nuclei, weaker orientation but more beta-crystals of the nucleated iPP.