SynopsisThermally stimulated depolarization current (TSD) method has been used to study the molecular relaxation from room temperature up to the glass-transition temperature for three plastically deformed polymers. A well-defined distinct a' peak has been observed in the vicinity of 70°C for polycarbonate, polysulfone, as well as poly(ethy1ene terephthalate), that had been annealed above Tg and subsequently cold-rolled. Since this relaxation is not observed after the initial measurements, it is a nonequilibrium relaxation. In the case of polycarbonate, the nonreversible a' process had an activation energy ranging from 1.22 to 1.75 eV and an intensity proportional to the degree of deformation resulting from cold-rolling. The spontaneous polarization in the rolled material was believed to originate from the initial anisotropy which was subsequently enhanced by the rolling process. Density measurements, as well as the birefringence observation, have been performed on the rolled specimens. All the studies led to the conclusion that the molecular motion responsible for this a' peak was the disorientation of local chain segments from their aligned conformation frozen in during the cold-work.
SynopsisThe low-temperature /3 relaxation has been studied via thermally stimulated depolarization current (TSD) method for polycarbonate that had been cold-rolled and subsequently undergone the a' relaxation at 70°C as a function of time. It has been found that the intensity of the p process increased as the annealing at 70°C increased. The analysis of the activation energy spectrum associated with the /3 relaxation indicated that the enhancement in the /3 intensity was due to the liberation of local dipoles from their aligned orientation as a result of undergoing the a' relaxation process. Tensile flow curves have also been determined for the same set of specimens. Similar enhancement was also observed in the yield stress behavior. In view of the good correlation between the mechanical property and the structural change revealed by the relaxation study, it was concluded that the variation of the yield stress and the work-hardening in the rolled polymer was primarily associated with those parts of the chain that had been disoriented from their frozen-in conformations.
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