Thermo-Oxidative Behavior of Carbon Black Composites for Self-Regulating Heaters

Abstract

The composite materials for self-regulating heaters are conductive composites based on a polymer matrix and a dispersed conductive filler consisting in either carbon black or another carbon material, such as graphite or nanotubes. Similar materials are suitable for sensors and current limitations. As these materials used in heating applications work usually at elevated temperatures in presence of air, the ageing processes would be an important limiting factor of their lifetime. Therefore, thermal oxidation processes and crystallinity changes during the service of these products are of major interest in durability studies. The potential interference of carbon-based materials with the oxidation and ageing of polymer matrix shall be known in order to correctly estimate the durability of such materials. The effect of radiation exposure is studied taking into account the potential use of such materials in radiation environments. In this work, the activation energies of some initial, unaged and aged products at elevated temperatures are compared in order to characterize the effect of thermo-oxidative ageing and hence to evaluate their durability. The effect of some antioxidants is also discussed. The crystallinity, calculated from DSC was used for evaluation of the physical changes induced within the aged materials, following the procedures described in previous work. FTIR-ATR technique was used for characterization of chemical changes induced by ageing.