Shear-Induced Crystallization of Poly(ε-caprolactone). 2. Evolution of Birefringence and Dichroism

Abstract

We have studied the crystallization of poly(e-caprolactone) (PCL) with in situ optical rheometry and ex situ optical microscopy as a function of applied stress. The evolution of the birefringence and dichroism was monitored in parallel with the viscosity following a temperature jump from the melt to a final crystallization temperature for different values of stress. In optical microscopy we found an increased nucleation density which resulted in the speed-up of the crystallization process in the strained samples as detected by optical rheometry. Changes in the crystal structure observed in optical microscopy were found to correlate well with the evolution of birefringence and dichroism. An increasing volume fraction of axialites at early times and crystal branching and randomization in orientation at later times were found to control the signal from optical rheometry. A decoupling of the evolution of shear viscosity from the optical rheometry signals has been observed at high shear stress attributed to pa...