Multiple relaxation investigations in polyetherimide: Thermally stimulated depolarization current technique

Abstract

127-133Thermally stimulated depolarization current (TSDC) technique has been used for investigating various dielectric relaxation processes in polyetherimide. The TSD currents in the temperature range 20º-250ºC (in certain cases up to 300ºC) were obtained as functions of polarizing field (Ep; 20-350 kV/cm), polarizing temperature (Tp; 60 º-180ºC), poling time (tp; 0.5-2 h), sample thickness (d; 25-120 µm), heating rate (h; 2º-6ºC/min), and storage time (ts; 0-552 h). The current maxima in the TSDC spectra reveal the presence of two major relaxation processes termed as β- (around 130ºC) and ⍺- (around 190ºC), associated with dipolar relaxation and space-charge relaxation processes, respectively. However, in certain cases, we observe merging of β- and ⍺-relaxation processes to become the ⍺β-relaxation process (140º-180ºC). The observed dependence of the peak temperature Tm on polarizing temperature and poling time indicates a continuous distribution of relaxations. The high Ep/Tp samples also show a relaxation (ρ) around 260ºC associated with charge injection phenomenon. The low temperature region of TSDC spectra (30º-70ºC) shows the presence of a weak relaxation (β′), considered as a satellite of the main dipolar relaxation process. The activation energies for various relaxation processes have been calculated using Bucci plot method