Electrical conductivity effects in polyethylene terephthalate films

Abstract

Electrical conductivity effects in biaxially stretched polyethylene terephthalate (PET) films of 6 μm thickness and 68% degree of crystallinity were investigated by means of dielectric relaxation spectroscopy in the frequency range 10−2–106 Hz and at temperatures higher than the glass transition temperature (∼85 °C) up to 190 °C. The formalisms of complex permittivity, electric modulus, and impedance were employed to analyze the experimental data. The results are discussed in terms of dc conductivity, conductivity current relaxation, interfacial Maxwell–Wagner–Sillars polarization, ρ peak, space-charge polarization, and electrode polarization. They are compared with the predictions of models for the electrical and dielectric properties of ion-conducting polymers. The dc conductivity values determined from dc measurement, from ac conductivity plots and from complex impedance plots agree well with each other. Their temperature dependence is described by the Vogel–Tammann–Fulcher equation and classifies PET as a fragile system.