G. Floudas et al., Shear-induced crystallization of poly(epsilon-caprolactone). 2. Evolution of birefringence and dichroism, MACROMOLEC, 33(17), 2000, pp. 6466-6472
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
.