CO2-induced Crystallization of Isotactic Polypropylene by Annealing Near Its Melting Temperature

CO2-induced crystallization of isotactic polypropylene (iPP) by annealing had been studied using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). The iPP before annealed was in α-form and amorphous states. At lower temperatures by CO2 isothermal treatments, iPP chains crystallized from the amorphous phase and only one crystal form, i.e., α-form, was observed. At higher temperatures by CO2 isothermal treatments, both crystallization from the amorphous phase and thickening of existing crystal lamellae were observed. Moreover, light γ-form crystal appeared in the treated iPP. The crystalline lamellar thickness of iPP annealed at different CO2 pressures had been determined. Using the Gibbs–Thomson plot method, the equilibrium melting temperature was found to be 187.6°C.