Les phenomenes de relaxation non isotherme dans les copolymeres ethylene-acetate de vinyle—I. Courants de depolarisation thermique

Abstract

Depolarization thermocurrent curves for ethylene-vinyl acetate copolymers, previously polarized by the thermoelectret effect at a temperature higher than the glass transition temperature, have been compared with dielectric loss curves described in the literature, in order to establish a possible relation between thermocurrents and the intrinsic relaxation phenomena. The two main peaks observed correspond to loss peaks described in dielectric measurements and result from primary and secondary dipolar relaxation, i.e. α and β type relaxation, respectively. We systematically used a partial polarization method consisting of polarizations in restricted temperature zones during a slow linear cooling of the sample, to describe the specific properties of these peaks. In this manner, we showed that the β relaxation, poorly resolved by dielectric measurements, consists of three discrete components having comparable activation energies, each of them presenting a distribution of the characteristic relaxation time. On the other hand, the amplitude of the α relaxation was found to be one order of magnitude higher than that of the β relaxation. It was characterized by a dipole concentration dependence of the activation energy and also presented an important distribution of characteristic relaxation times.