Electrical approach to monitor the thermal oxidation aging of carbon black filled ethylene propylene rubber

The main objectives of this work are (1) to establish the correlation between changes in the electrical conductivity (resistivity) and the mechanical properties (ultimate tensile elongation) of a carbon black filled ethylene propylene rubber (EPR) during thermal oxidative oven aging at 125 °C and (2) to show the feasibility of using the resistivity change as a non-destructive monitor method of the aging process. Elongation, weight, density and resistivity were followed versus aging time for EPR samples loaded with 21.6 and 26.2 wt% carbon black. Assuming a typically chosen mechanical failure criterion (elongation reaches 50% absolute), the drop in resistivity at “failure” is found to be on the order of a factor of 10 for both materials. Analyses of weight and density changes indicated that the substantial resistivity decreases were due to increases in volume fraction of the conductive carbon black caused mainly by the mass loss of polymer matrix and sample shrinkage during the thermal oxidation aging process. The results offer strong evidence that resistivity measurements could represent a very useful and non-destructive cable monitor approach.