Dielectric properties of ETFE wiring insulation as a function of thermal exposure

Ethylene-tetrafluoroethylene (ETFE) is one of several polymers used in electrical insulation of aircraft wiring. The integrity of the insulation is important to the aerospace industry due to potential catastrophe in the event of an electrical fire caused by breakdown of the wiring insulation. In this work, the relative permittivity of ETFE is studied in order to examine the feasibility of developing a capacitive nondestructive testing method to indicate degradation-induced permittivity changes. One degradation mechanism is exposure to heat. To obtain baseline permittivity values, the permittivity of injection-molded but otherwise untreated ETFE was measured over the frequency range 1 Hz to 1 MHz at various temperatures from -150 to 210°C, using a Novocontrol dielectric spectrometer with a temperature-controlled sample cell. Then, ETFE samples were annealed at 60°C for 2 hours and isothermally heated at 160°C for up to 96 hours. Measurements of permittivity over the frequency range 1 kHz to 2 MHz, obtained using an Agilent E4980A LCR meter, revealed changes of around 0.05 in the measured relative permittivity of the thermally-exposed samples, compared with the baseline sample.