Temperature Dependence of Hydrolysis of Polyimide Wire Insulation

Degradation of polymeric materials as a chemical reaction rate, related to exposure temperature, has been confirmed by many laboratory studies, and the rate equation, enhanced by other stresses and environmental conditions, has been utilized to compare the service life expectancy of various electrical insulation materials and systems for many years. In recent Naval aircraft wiring applications it has been experienced that a popular polyimide insulation undergoes degradation by a hydrolytic chain-splitting reaction that can be attributed to an unexpected number of service failures. In this initial study it has been determined that the reaction does proceed in a neutral pH aqueous environment at a rate that is temperature dependent, and the data of life versus temperature conforms to an Arrhenius plot so that from accelerated tests at elevated temperatures it is possible to extrapolate to service temperatures. Continuing studies will lead to the development of a functional aging procedure for applying a moisture exposure step into each cycle in order to more nearly predict service life of this insulation system and provide a comparison with other candidate systems.