Dagmar Svobodova

Effect of initial melting temperature on crystallization of polypropylene/organoclay nanocomposites

Polypropylene (PP) nanocomposites were prepared by melt intercalation using an intermeshing co-rotating twin-screw extruder. The influence of organoclay (Cloisite 20A) and maleic anhydride modified polypropylene (PP-MA) on various properties was explored. The effect of the initial melting temperature on crystallization kinetics was investigated by differential scanning calorimetry (DSC) and optical microscopy. DSC has revealed a gradual decrease in crystallization kinetics with an increase in initial melting temperature for two-component systems (PP/PP-MA and PP/20A). However, in the case of a three-component system (PP/PP-MA/20A), the decrease of crystallization kinetics in the range of initial melting temperature being 200–240 °C was followed by an increase in the temperature range 240–260 °C. After initial melting at 250 °C, many spherulites were discovered in the three-component system. This unusual crystallization behavior was explained with the help of Fourier transform infrared spectroscopy (FTIR), where an increase in the Si-O peak with the increasing initial melting temperature was detected, which indicates the presence of large surface of clay layers. The morphology of nanocomposites was also investigated by transmission electron microscopy (TEM). The X-ray diffraction (XRD) analysis has revealed a decrease in the peak intensity with an increase in initial melting temperature, which suggests exfoliation caused by fast diffusion at high temperatures.