CHARGING AND DISCHARGING CURRENTS IN COMPOSITE POLYAMIDES

This paper describes the results of investigations carried out into ch arging and discharging currents in Nomex-Polyester-Nomex Polyamide she ets of 152 mu m thick over a temperature range of 25 - 200 degrees C a nd electric field strengths of 0.1 - 10MV m(-1) The currents are measu red as a function of time up to 10(5)s and the influence of time durat ion, temperature, electric field, electrode material, and field polari ty are investigated. From the measured charging and discharging curren ts, transport currents are evaluated under isothermal conditions. Two distinct regions of electric field, in which the dependence of current on field changes from linear to exponential, are identified. In the h igh field region, the transport mechanism is suggested to be ionic wit h a possible secondary contribution from Poole-Frenkel effect. The low frequency loss factor is evaluated from the discharging currents and a relaxation time of 1.7 x 10(4)s at 70 degrees C with an activation e nergy of 0.38 eV is obtained.