Dielectric spectroscopy - an analytical tool for monitoring the deterioration due to high energy radiation in ethylene propylene diene terpolymer (EPDM) vulcanizates

Abstract

This paper demonstrates the use of a dielectric spectroscopy technique for monitoring the high energy radiation ageing and stabilization of ethylene propylene diene terpolymer vulcanizates. The measurement of dielectric constants and dielectric losses in the frequency domain help to quantify the physico-chemical changes in the bulk due to high energy irradiation. It is found that the relaxation time calculated using an empirical approach is exponentially related to the total exposed dose. A quantitative comparison of different antirads with a control vulcanizate has been demonstrated by using parameters defined as relative efficiency indices (REI) and relative stability indices (RSI). Three types of REI parameters are defined and computed from dielectric measurements after irradiation over a period of time at a fixed frequency. These REI values are a good estimate of antirad efficiency for energy scavenging and transient charge scavenging. Two types of RSI parameters are defined and computed from the frequency scans of dielectric properties for a material exposed to various doses of γ irradiation. These RSI values provide a good estimate of the rate and extent of changes in the physico-chemical structure due to irradiation. A third type of RSI, computed from equilibrium swelling measurements, closely matches that obtained from dielectric data. It is concluded that the deterioration is predominantly created by a cross-linking reaction even after the addition of antirads. It is observed that polymeric antirads provide the highest efficiency stability.