Study of polarization parameters effect on dipolar relaxation in epoxy-based polymer using thermally stimulated depolarization current

Research Unit, Physics of Insulating and Semi-Insulating Materials, Faculty of Sciences, University of Sfax, B.P. 1171, 3000 Sfax, Tunisia

^a e-mail: fatma_namouchi@yahoo.fr

Received: 6 April 2013
Revised: 21 October 2013
Accepted: 20 January 2014
Published online: 3 March 2014

Abstract

In this paper, dipolar relaxation processes in epoxy-based polymer were investigated under various polarization conditions, using thermally stimulated depolarization current (TSDC) technique. The TSDC spectrum of un-poled epoxy polymer reveals an unusual negative current, associated with a thermally generated charge carriers, which were due to impurities ionization and structural changes mainly at high temperature (above T_g). β and α dipolar relaxations were detected respectively around 115 °C and 154 °C in conventionally poled sample at T_P=110 °C and E_P= 3 kV/mm. Dipolar relaxation parameters were evaluated using two techniques: (1) theoretical decomposition of global complex TSDC spectrum, using Bucci-Fieschi expression based on single Debye process, (2) experimental procedure based on selective polarization, commonly known as windowing polarization (WP). The obtained values are T_P dependent: relaxation time decreases and activation energy increases when polarization temperature increases. An ω relaxation peak due to water molecule departure was detected around 135 °C, using WP techniques for T_P=100 °C Unlike dipolar relaxations, its position is independent of polarization temperature. Complementary thermal analysis investigations by differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA), were made to support some given conclusions.