Crystallinity of isotactic polypropylene films annealed from the quenched state

Quenched isotactic polypropylene films were annealed at 130, 140 and 155 °C for 24 h. The structural organization, after annealing, was analysed by wide-angle X-ray diffractograms (WAXD), differential scanning calorimetry (DSC), density and sorption of dichloromethane vapour at low activity. The comparison of the different methods used to obtain the crystallinity shows that, even at the highest annealing temperature, the transformation of the smectic phase into the monoclinic phase, is not complete. WAXD and DSC give the amount of monoclinic phase, whereas the amorphous fraction was derived from sorption of dichloromethane vapour at low activity. From the density, it was possible to derive the residual smectic fraction in the different samples. The results indicate that, at temperatures higher than 150 °C, there is an accelerated decrease of smectic phase and an accelerated increase in the crystal dimensions and perfection.