Effect of mechanical deformations on thermally stimulated currents in polymers. I. Uniaxially cold-drawn polycarbonate

The thermally stimulated depolarization and polarization current (TSDC and TSPC) methods have been used to study the intermediate relaxation induced in polycarbonate by uniaxial cold drawing at various drawing ratios and rates. No spontaneous polarization resulting from molecular orientation or internal stress was evidenced by current measurements under zero bias voltage. The intermediate α´ relaxation was generated in TSPC and subsequent TSDC experiments, but its properties were markedly different in the two types of spectra. In TSPC measurements, the molecular mechanism responsible for the α´ peak is probably a field-induced local orientation of chain segments made possible by the increase in free volume consecutive to the drawing process. During this polarization step, which involves a thermal treatment of the drawn material up to 100°C, a progressive change in structure and dipolar environment occurs, and this tends to shift and broaden the relaxation as seen in subsequent TSDC cycles