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.

Polymer Composites with Self-Regulating Temperature Behavior: Properties and Characterization

“…The list of abbreviations used in this manuscript are presented in Table 1. As conductive fillers, carbon black (FEF type) and natural graphite (CR10) were used (see [22] for more details).…”

“…DSC measurements were performed in non-isothermal mode, under e dation tests) or nitrogen (melting/crystallinity tests), using a DSC 131 ev (Setaram, Lyon, France). The parameters describing the oxidation (OOT, o oxidation heat) were calculated from the thermograms as described in refer The melting/crystallinity peaks, the melting/ crystallization temperatures, an effects associated to either melting or crystallization were calculated as des in the reference [22]. The crystalline content (Xc) of the material was calcula tions presented in reference [22], using a value of 279 J/g for melting entha crystalline polyethylene [28].…”

“…The parameters describing the oxidation (OOT, oxidation rate, oxidation heat) were calculated from the thermograms as described in references [26,27]. The melting/crystallinity peaks, the melting/ crystallization temperatures, and the thermal effects associated to either melting or crystallization were calculated as described earlier in the reference [22]. The crystalline content (X c ) of the material was calculated by equations presented in reference [22], using a value of 279 J/g for melting enthalpy of totally crystalline polyethylene [28].…”

“…The melting/crystallinity peaks, the melting/ crystallization temperatures, and the thermal effects associated to either melting or crystallization were calculated as described earlier in the reference [22]. The crystalline content (X c ) of the material was calculated by equations presented in reference [22], using a value of 279 J/g for melting enthalpy of totally crystalline polyethylene [28].…”

“…In general, improvement of the properties of PTC materials requires compositional optimization of both polymer matrix and conductive fillers [17]. Polymer blends and synergic mixtures of different conductive powders are of actual interest in this direction [5,17,21,22].…”