Characterizing and quantifying the aging of polyethylene thin films using novel doped-films and gold nanoparticle labeling strategies toward understanding failure of cabling insulation

Under environmental driving forces, the polymer backbone of the cabling insulations undergo oxidation, scission and crosslinking reactions that ultimately lead to changes in the physical properties of the plastics. The aim of this work is to develop new methods for quantifying rates and yields of chemical changes within the relevant insultation polymers and relate these changes to changes in the electrical barrier properties of the materials. Specifically, novel methods were employed for quantifying oxidation and crystallinity within thin films relying on attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR). Oxidation was quantified using doped films as solid-state calibration standards. The percent crystallinity was also determined by normalization of amorphous and crystalline IR-stretches. To observe electrical property changes, we applied electrochemical impedance spectroscopy with solutions of either gold nanoparticles (4-6 nm diameter) or a gold salt solution. Under the applied conditions, a drop in impedance was observed and predicted to be the result of Au³⁺ ion penetration into the aged films. Combining the ATR-FTIR measurements of oxidation and crystallinity, along with the impedance measurements, we have established a suite of strategies for evaluating polymers that will ultimately enable a predictive model for the failure of these plastics as insulators of electrical cables.