CONTINUOUS COOLING AND ISOTHERMAL CRYSTALLIZATION OF POLYCAPROLACTONE

摘要

In this article we present overall crystallization characteristics of five polycaprolactone samples with mean molecular weights ranging from 50,000 to 400,000. The crystallization temperatures and heats of crystallization are determined as a function of mean molecular weight as well as for cooling rates in the range 0.31 to 40 K/min. Our results show a decrease in crystallization temperature from 320 to 300 K at increasing molecular weight and cooling rate. The heat of crystallization shows a slight decrease within the cooling rate interval and a decrease from about 68 to 48 J/g with increasing molecular weight. We analyze the continuous cooling data according to the Ozawa model for nonisothermal crystallization and compare them with our isothermal data analyzed with the Avrami model. Both the Ozawa and Avrami models give exponent parameters in the range 2.9 to 3.6. In the investigated temperature range and for all samples, we find a nucleation controlled crystallization. At the lowest temperatures, the Ozawa analysis indicates an increasing dependency on limitations in chain mobility. The higher molecular species have in general a slower crystallization rate, with half crystallization times increasing with a factor of about five within the molecular weight range at 320 K. (C) 1996 John Wiley & Sons, Inc. [References: 40]