Dielectric relaxation spectroscopy of polyethylene terephthalate (PET) films
(EN)
Neagu, E
(EN)
Gomez Ribelles, JL
(EN)
Apekis, L
(EN)
Pissis, P
(EN)
The dielectric properties of biaxially stretched polyethylene terephthalate (PET) films of 6 mu m thickness and 68% degree of crystallinity were investigated by means of dielectric relaxation spectroscopy in the frequency range 10(-2)-10(6) Hz and the temperature range 20-190 degrees C. Differencial scanning calorimetry (DSC), in the range 50-300 degrees C, was employed to investigate the thermal properties of the PET samples. Besides measuring the alpha relaxation associated with the glass transition and the secondary beta relaxation, special attention has been paid to the investigation of DC-conductivity-related effects. They give rise to high dielectric permittivity values and dielectric losses at low frequencies and high temperatures. The results are analysed within the complex permittivity formalism and discussed in terms of interfacial Maxwell-Wagner-Sillars polarization, the rho peak, conductivity relaxation, space-charge polarization, electrode polarization and DC conductivity. DC conductivity values determined from frequency plots of the AC conductivity follow the Vogel-Tamman-Fulcher equation at temperatures higher than the glass transition temperature, indicating that the charge-carrier transport mechanism is governed by the motion of the polymeric chains. On the basis of the temperature dependence of the DC conductivity PET is classified as a fragile system.
(EN)
