Developing a Predictive Model and Novel Imaging Technique for the Failure of Polyethylene Insulators

Abstract

Polyethylene is the most widespread polymer used in insulative cable housings due to its low cost, high chemical resistivity and low permeability to liquids and gases. This does not mean, however, that the material is not susceptible to failure under environmental working conditions. Many techniques for monitoring both chemical and physical changes have been developed, though no attempts have been made to integrate these findings. Here, we put forth a model for the failure of polyethylene cable housings under thermooxidative conditions. This model revealed an absence of data on the monitoring of polyethylene crystalline structure during the aging process, which in part controls the insulative properties of the polyethylene. Polyethylene films (30 µm) were aged at 110°C for 24-hour periods in an oven and carbonyl content, a common aging indicator, was monitored. An ATR-FTIR crystallinity monitoring technique was developed and revealed a 3-phase change of crystalline structure upon thermal aging. To better visualize the hypothesized pore formation in the polyethylene, which follows aging, EIS was used to saturate pores with gold nanoparticles before elemental analysis and imaging with SEM. Results suggest the existence of these pores and the ability for ions to penetrate the aged films.