Electrical and mechanical properties of carbon black filled ethylene propylene rubber during thermal oxidation aging

Abstract

Carbon black filled conductive polymers have wide applications, such as electrostatic dissipation, electromagnetic interference shielding, and pressure sensors. When such materials are used for long-term application, they undergo thermal oxidation aging reaction in the environment. So it is necessary to understand how the electrical resistivity changes with the aging process. The main objective of this work is to establish the correlation between electrical and mechanical properties of such materials during thermal oxidation aging. Ethylene propylene rubbers (EPR) loaded with 21.6 and 26.2 wt. % carbon black, respectively, underwent the accelerated thermal oxidation aging experiments. The electrical conductivity, physical, and mechanical properties of these materials were investigated. Resistivity of carbon black filled EPR decreased dramatically during the thermal oxidation aging process. The difference was as high as six orders of magnitude. The time when the significant change of resistivity occurred coincided with the time when changes of the other physical properties of the materials, such as density, and weight loss occurred. The mechanical properties of the materials failed after the substantial changes in electrical and physical properties had occurred. This resistivity change of the conductive polymer composite can be used to amplify the density change during the thermal oxidation aging, thus monitor the aging of conductive polymer composites. The experiments also showed the composite with more carhon black loading underwent a slower degradation than the composite with lower carbon black loading at the same experiment conditions. This was explained by the antioxidant effect of carbon black.