Crystallization from the melt at high supercooling in finely dispersed polymer blends: DSC and rheological analysis

Crystallization at high supercooling of polybutylene terephthalate (PBT) droplets dispersed in a molten polyethylene (PE) matrix was investigated through rheological and DSC experiments. The Palierne's emulsion model was used as a theoretical framework for studying the viscoelastic behavior of the blends in different ranges of temperature: on the one hand, when the two polymers are molten (T > 225 degrees C) and on the other hand, when PET droplets are at high supercooling in the molten PE matrix (130 degrees C < T < 205 degrees C). From rheological experimental evidences it was shown that molten and solidified droplets coexist at high supercooling. The Palierne's model was then successfully adapted to take into account the three phases (molten PE, molten PET droplets, and solidified PET droplets). The evolution of the behavior with the temperature is consistent with the growing amount of crystallized droplets. Moreover, a calculation taking into account the droplets size distribution and the number of nuclei is introduced to explain the crystallization behavior of three different blend ratios. (C) 1998 John Wiley & Sons, Inc.