Viscoelasticity as a tool to investigate the early stage of the quiescent crystallization process of poly(lactic acid)

Viscoelasticity was applied to monitor the early stage of the crystallization process of poly(lactic acid). The evolution of the storage modulus in the process was divided into three stages with the help of optical microscopy. A simple model, combining the kinetics of embryo population and the Palierne Equation for suspension, was proposed to describe the evolution of the storage modulus along the process. The model was extremely successful in portraying the rheological behavior. Rate constants related to the nucleation and the formation and dissociation of the embryo, as well as the Avrami parameter, could therefore be determined by the rheological tool. Although linear viscoelasticity is frequency dependent, the rate constants were found to be essentially independent of the frequency applied. The Avrami parameter was found to have a threefold change over a frequency range of more than two orders of magnitude, which could be an important reference for the frequency selection when implementing the rheological tool in the investigation of polymer crystallization.
INTRODUCTION The crystallization behavior of semicrystalline polymers is crucial in the final mechanical properties of the plastic products. Crystallization commonly occurs in industrial processing such as fiber spinning, die extrusion, [...]