Impedance spectroscopy (IS) consists of applying an alternating voltage and sweeping a frequency range. The current response of the sample is measured and then the resulting real and imaginary impedance can be used in a number of ways to describe the electrical characteristics of the polymer. In this manner, we can determine the sensitivity of IS to detecting changes in the polymeric material’s insulating capabilities due to a variety of environmental conditions. Both a liquid cell set up and dry cell set up were used for the IS experiments are shown in Figure 1.
In this project, we studied Physical aging (PA), Chemical aging (CA) and thermal aging of polymeric insulation used in aircraft wire. Physical aging of PVC film was performed at 45°C (Tg is 60°C), acetic acid was used for chemical aging and PVC wire insulation was thermally aged (TA) at 125ºC for several weeks. For controlled PVC films, the physical aging results showed that resistance of the film and its stiffness increases with aging time. In contrast, the conductivity of PVC increases and modulus and strength decreases with chemical aging due to polymer degradation. With thermal aging, resistance increases initially, however, after 10 weeks of TA, resistance dropped dramatically due to micro-cracking in the insulation layer.