Shear-induced crystallization of poly(epsilon-caprolactone). 2. Evolution of birefringence and dichroism

mie have studied the crystallization of poly(epsilon-caprolactone) (PCL) wi th in situ optical rheometry and ex situ optical microscopy as a function o f applied stress. The evolution of the birefringence and dichroism was moni tored 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 resul ted 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 b irefringence and dichroism. An increasing volume fraction of axialites at e arly 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 partial crystal melting. Application of a short step stress prior to crystallization is adequate to speed up the crystallization process due to the enhanced nucleation density .