CONTINUOUS COOLING AND ISOTHERMAL CRYSTALLIZATION OF POLYCAPROLACTONE

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 crys tallization are determined as a function of mean molecular weight as w ell as for cooling rates in the range 0.31 to 40 K/min. Our results sh ow a decrease in crystallization temperature from 320 to 300 K at incr easing molecular weight and cooling rate. The heat of crystallization shows a slight decrease within the cooling rate interval and a decreas e from about 68 to 48 J/g with increasing molecular weight. We analyze the continuous cooling data according to the Ozawa model for nonisoth ermal crystallization and compare them with our isothermal data analyz ed with the Avrami model. Both the Ozawa and Avrami models give expone nt parameters in the range 2.9 to 3.6. In the investigated temperature range and for all samples, we find a nucleation controlled crystalliz ation. At the lowest temperatures, the Ozawa analysis indicates an inc reasing dependency on limitations in chain mobility. The higher molecu lar species have in general a slower crystallization rate, with half c rystallization times increasing with a factor of about five within the molecular weight range at 320 K. (C) 1996 John Wiley & Sons, Inc.