Isothermal crystallization behaviors of isotactic polypropylene with ultrasonically‐modified calcium sulfate whisker as β‐nucleating agent

Abstract

AbstractIn this work, the effect of calcium sulfate whisker (CSW) and ultrasonically‐modified CSW (UCSW) on the crystal structure and isothermal crystallization of isotactic polypropylene (iPP) is studied by using differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and polarized optical microscopy (POM). UCSW obviously increases heterogeneous nucleation. The isothermal crystallization kinetics of pure iPP, iPP/CSW, and iPP/UCSW composites are analyzed by the Avrami method. Although the Avrami exponent (n) of these samples only changed slightly, the half crystallization time (t1/2) indicates that CSW and UCSW decrease the overall crystallization time and increase the crystallization rate (Rc). POM results show that most crystals are β‐iPP shaped and the spherulite size decreases significantly with the addition of UCSW. The apparent equilibrium temperature of iPP/UCSW composites is lower than that of pure iPP and iPP/CSW composites. The values of β‐iPP fold surface free energy (σe) and the nucleation parameter (Kg) are much lower than that of α‐iPP for these iPP composites. The content of β‐crystal in iPP composites increases due to the addition of UCSW.