Effect of shearing on crystallization behavior of poly(ethylene terephthalate)

The shear-induced crystallization behavior of PET was investigated by measu ring the time-dependent storage modulus (G') and dynamic viscosity (eta') w ith a parallel-plate rheometer at different temperatures and shear rate. Th e morphology of shear-induced crystallized PET was measured by DSC, X-ray, and polarizing optical microscopy. When a constant shear rate was added to the molten polymer, the shear stress increased with the time as a result of the orientation of molecular chains. The induction time of crystallization is decreased with frequency. Moreover, the rate of isothermal crystallizat ion of PET was notably decreased with increasing temperature. The shape of spherulites is changed to ellipsoid in the direction of shear. In addition, aggregation of spherulites is increased with increasing frequency. Particu larly, the row nucleation morphology could be observed under polarized ligh t for omega = 1. From the results of DSC, the melting point and enthalpy ha ve a tendency to decrease slightly with increasing frequency. The crystalli te size and perfectness decreased with frequency, which was confirmed with X-ray data. The unit length of the crystallographic unit cell of the PET in creased and the ((1) over bar 0 3) plane peak increased with increasing fre quency. (C) 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2640-2646, 20 01.