Crystallization kinetics of oriented polymers

Abstract

AbstractThe increase in the rate of polymer crystallization brought about by mechanical deformation above the polymer glass‐transition temperature is examined. For flexible macromolecules, this deformation results in alignment and extension of polymer chains. By hypothesizing that the instantaneous growth rate at a given constant temperature depends uniquely on the polymer chain orientation in the surrounding melt, an explicit expression is obtained for the growth rate of a spherulite in terms of experimentally measurable quantities. Isothermal meltspinning experiments were conducted with poly(ethylene terephthalate) (PET) using a laboratory setup. Very large values of the total crystallinity and significantly enhanced values of the crystallization rate were generated by operating at different temperatures that straddle the temperature of maximum crystallization rate for the quiescent melt. Measured rates of crystallization do, indeed, correlate with the instantaneous amorphous orientation. Furthermore, a masterplot, independent of temperature, is obtained by normalizing the crystallization rate under spinning conditions with that under quiescent conditions. This is the first time that such data have become available, and, given the processing history, such a master plot should be of use in predicting the crystallinity levels in actual nonisothermal industrial experiments.