Liquid–liquid phase separation and its effect on crystallization in the extruded polypropylene/ethylene–propylene–rubber blend

Abstract

The liquid–liquid (L–L) phase separation and its effect on crystallization in polypropylene (PP)/ethylene–propylene–rubber (EPR) blend obtained by melt extrusion were investigated by time-resolved light scattering (TR-LS), optical microscope and small-angle X-ray scattering (SAXS). The existence of the lower critical solution temperature (LCST) was found by the kinetic analysis of the L–L phase separation, that is, the apparent diffusion coefficient of spinodal decomposition (SD), obtained by the TR-LS, decreased with increasing temperature. The L–L phase-separated specimen at 190°C for various time periods was subjected to a temperature-drop to 130°C for the isothermal crystallization and then investigated effect of L–L phase separation on crystallization. Memory of L–L phase separation via SD remained even after crystallization and crystallization proceeded only in PP-rich phases. The crystallization rate decreased with increasing L–L phase-separated time at 190°C. The rapid crystallization for short L–L phase-separated time could be ascribed to the elevation of chain mobility of PP by relatively higher amounts of EPR in PP-rich phases. The amount of EPR between PP lamellae in PP-rich phases was quantified using the correlation function, which is given by the fourier transform of the SAXS intensity.