Crystallization of Poly(phenylene sulphide) with Different Molecular Weights under Shear Condition

The crystallization morphology of poly(phenylene sulphide) (PPS) with different molecular weights (MW), isothermally crystallized from the melt under shear condition, has been observed by polarized optical microscope (POM) equipped with a CSS450 hot-stage. The morphology of PPS is greatly influenced by shear condition, and the shish-kebab-like fibrillar crystal structure can be observed under higher shear rate and longer shear time for the higher molecular weights . Under the quiescent crystallization the growth rate was found to be essentially MW dependent i.e., the spherulite growth rate decreases with the increased MW, and a strong effect of MW on the flow induced crystallization kinetics was observed. Under shear condition the decreasing spherulite growth rate results from highly oriented chains. The molecular weight was also found to explain qualitatively the observed transition from the lowest MW isotropic morphology to the higher MW shish-kebab-like fibrillar crystal structure. The melting behaviors of the three MWs performed by differential scanning calorimetry (DSC) show that multiple melting peaks can be observed after the PPS melts when subjected to shear flow. We suggest that the lower melting peak corresponds to the melt of imperfect crystal. The higher melting peak is related to the orientation of molecular chains . These orientated molecular chains form the initial lamellae, which are thicker than the kebab-like lamellae that later develop due to chain relaxation .