Analysis of the thermally stimulated discharge current around glass-rubber transition temperature in polyethylene terephthalate

Abstract

The nature of the thermally stimulated discharge current (TSDC) for polyethylene terephthalate samples in the temperature range from room temperature to above glass-rubber transition temperature of the amorphous phase is analyzed. The well conditioning of the sample is strictly necessary in order to have a good reproducibility and accuracy of results. A main peak was observed whose maximum temperature moves towards a lower value with the decreasing of the amount of charge that flows through the sample during polarization. The peak position changes as well, if the sample is polarized in air or in oxygen and the nature of change is more important in the case of oxygen. The shape of the peak is complex and at least four shoulders have been identified around 85, 90, 105, and 125 °C using the cleaning technique. The activation energy tends to increase with repetition of the TSDC runs, in the glass-rubber transition temperature range, in the case when the cleaning technique is used for the peaks separation. For the conditioned samples, there is a good agreement between the experimental results and the analytical expression of the current, particularly in the region where it reaches a maximum, and so relevant values for the characteristic parameters of the peak are determined. The time interval of the short circuiting of the sample, at room temperature, before the TSDC measurement, strongly influences the initial rise of the current and consequently the parameters of the peak. A possible redistribution of the internal field arising from the injected charge, the heterocharge, and the existing charge in the sample as received, has been put forward to account for the experimental evidences. The conclusion is that the current is mainly determined by the space-charge released from the traps that are likely continuously distributed in energy. For the stated polarization conditions, the charge is released from the shallow traps with an activation energy in the range 0.23–0.32 eV and a concentration of ∼1018/m3. The dipolar charge is of little importance.

Electrical conductivity effects in polyethylene terephthalate films

“…Thermally stimulated depolarization currents ͑TSDC͒ measurements on PET samples show a peak at temperatures higher than the ␣ peak associated with the glass transition, 9,11,12,[24][25][26] in agreement with measurements on many other polymeric systems. This is the so-called peak, which is attributed to space-charge polarization.…”

TSDC study of structural relaxation on polyethylene terephthalate

“…The a peak appears close to the glass transition temperature as determined by DSC, and can be attributed to the micro-Brownian motions of large chain segments. The value 4.03 eV of the activation enthalpy calculated by peak integration method [22,23], in the vicinity of the glass transition characterizes a main relaxation mode [24]; this value is close to that calculated by Neagu et al [22]. The high temperature peak (q-peak), whose origin is related to space charges [25] depends strongly on sample preparations and poling conditions.…”

Thermally Stimulated Depolarization Current and Thermal Analysis Studies of Gamma Irradiated Lithium‐Salt/Polymer Electrolyte Blends

“…The current density released during thermally stimulated current measurement can be expressed in the general form [11,12] JðTÞ…”