STUDY ON LIQUID-LIQUID PHASE-SEPARATION AND ITS EFFECT ON THE CRYSTALLIZATION KINETICS OF BLENDS COMPOSED OF ISOTACTIC POLYPROPYLENE/ETHYLENE-PROPYLENE RUBBER

Abstract

The liquid-liquid phase-separation (LLPS) and isothermal crystallization behavior of isotactic polypropylene / ethylene-propylene rubber blend (iPP/EPR) were investigated by using small angle laser light scattering (SALLS),differential scanning calorimetry (DSC),phase contrast microscopy (PCM) and polarized optical microscopy (POM).Results reveal that LLPS of (50/50,W/W) iPP/EPR blend happens at temperatures above the melting point of iPP,and its kinetics follows the spinodal decomposition (SD) mechanism.The apparent diffusion coefficient (D_ app ) and the spinodal temperature (T_s) of the iPP/EPR samples were calculated on the basis of the Cahn-Hilliard theory.Moreover,it is found that the D_ app increases with the increase of temperature,representing the LCST behavior of iPP/EPR.The development of phase morphologies could be obtained by quenching in liquid N_2 the iPP/EPR samples subjected to annealing with different time at 200℃.On the other hand,the structure of iPP/EPR melt appears nearly homogenous at the beginning of LLPS.Furthermore,the co-continuous phases form,and the phase connectivity grows until macroscopic spherical texture generates.Both the increases of phase separation time (t_ ps ) and phase separation temperature (T_ ps ) result in the decrease of the crystallization rate.The kinetic results indicate that the Avrami model is qualified for describing the isothermal crystallization of iPP/EPR.It is believed that the degree of phase-separation has little effect on the crystallization kinetics and the crystallization gives priority to instantaneous nucleation and three-dimension-growth.