Material behaviourInfluence of supercritical CO2 and initial melting temperature on crystallization of polypropylene/organoclay nanocomposite

Polypropylene (PP)/clay nanocomposite with maleic anhydride modified polypropylene (PP-MA) was prepared using a twin-screw extruder. The effect of supercritical carbon dioxide (scCO2) on mixing was investigated. Isothermal crystallization of the nanocomposites was investigated by differential scanning calorimetry (DSC) and also by optical microscopy as a function of initial melting temperature. Increasing initial melting temperature causes a gradual decrease in bulk crystallization kinetics, with the exception of the 240-260 °C temperature range for the system without CO2. Optical microscopy revealed a large number of small spherulites for the system without CO2 after initial melting at 250 °C. After 28 min initial induction period of crystallization many small spherulites appeared in the vicinity of large spherulites for the system with CO2, indicating the beginning of homogenous nucleation. X-ray diffraction (XRD) and direct observation of the samples after tensile testing revealed better dispersion of nanoclay for the system without CO2.