Simultaneous liquid-liquid demixing and crystallization and its effect on the spherulite growth in poly(ethylene terephthalate) poly(ether imide) blends

Poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blends were miscible in the melt, but exhibited simultaneous liquid-liquid phase separation and crystallization over a wide range of temperature and composition. The interplay between these two processes is expected to dominate the morphological formation in the blends. In this study, the phase diagram of PET/PEI blend was determined to evaluate the envelop within which liquid-liquid phase separation was operative with crystallization. A UCST phase diagram below 240 degrees C was identified for this system. The effect of liquid-liquid phase separation on the growth of PET spherulites was studied by small-angle light scattering (SALS). Nonlinear spherulite growths were observed for the blends at higher crystallization temperatures of 210 degrees C and 220 degrees C, while the growths were basically linear below 210 degrees C. The nonlinear growth behaviour was discussed based on the competition between spherulite growth and spinodal decomposition. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.