Isothermal crystallisation of iPP/Vectra blends by DSC and simultaneous SAXS and WAXS measurements employing synchrotron radiation

Abstract

The isothermal crystallisation behaviour and morphology of blends of isotactic polypropylene, iPP, and a liquid crystal polymer, Vectra A950, has been studied using differential scanning calorimetry, optical microscopy and simultaneous WAXS and SAXS in real-time measurements using synchrotron radiation. It has been observed that Vectra domains act as sites for the nucleation of iPP, and the rate of crystallisation is enhanced with increasing Vectra content in the blend. The presence of the α crystalline form in pure iPP, and both α and β forms for iPP in iPP/Vectra blends has been found. The SAXS patterns for iPP/Vectra blends containing β iPP are characterized by two different long period values that were related to the α and β lamellae. The secondary crystallisation mechanism has been investigated by SAXS/WAXS experiments. It is shown that, in contrast to primary crystallisation, secondary crystallisation of iPP is not affected by the presence of the thermotropic liquid crystalline polymer. As already known from pure iPP, the main process of secondary crystallisation is the growth of new lamellar stacks within remaining amorphous regions in the iPP spherulites.