Identification of life model parameters for electro-thermally stressed PET films

Electrical and multistress life tests were performed on 50-μm-thick, biaxially stretched PET (polyethylene terephthalate) films that were aged with stainless steel contact electrodes at temperatures of 20, 60, 110, 130, and 150°C and under 0.5, 0.65, 0.8, 1.0, 1.5, 2.0, and 2.5 kV at 50 Hz. Analysis shows that life data for simultaneous thermal and electric aging of PET films can be described by curvilinear threshold life models, especially for lower aging temperatures. A good data fit is obtained for both exponential and inverse power models, although the temperature dependences of the threshold value indicate that the exponential models describe the material´s physical behavior better. Exceeding the glass transition temperature does not cause significant changes in the threshold value, whereas aging at higher temperatures, where recrystallization takes place, influences the electrical threshold strongly