Effects of Heat Treatment and Mechanical Stresses on the Dielectric Strength of Uniaxially Drawn Pet Film

The dc dielectric strength of uniaxially drawn polyethylene terephthalate (PET) film has been investigated under compressive stresses. The drawn samples are heat-set in a silicone oil bath over a temperature range from 100 to 220°C for durations of 1 and 60 min in order to control the degree of crystallinity of the samples. The dc dielectric strength under no mechanical stress is found to increase with heat-setting temperature regardless of the heat-setting time. The compressive stress value showing maximum dielectric strength under compression has decreased significantly with increase in the heat-setting time and heatsetting temperature. The results obtained are discussed in terms of the morphological and mechanical properties of the samples.