Influence of heating rate and atmospheric conditions on the thermal response of CFRP and its constituents

Abstract

The thermal stability of carbon fibre-reinforced polymer (CFRP) and its constituents (neat epoxy resin and carbon fibre) are studied in terms of mass loss using a thermogravimetry technique at different heating rates and two atmospheric conditions (air and pure nitrogen). By interpreting the mass loss over a temperature range of 25–900 °C, it was possible to identify the specific mechanisms of polymer degradation. In an oxygen-free pure nitrogen atmosphere, the thermal degradation of epoxy resin used as the composite's matrix is strongly inhibited up to the temperature of 400 °C, after which it undergoes thermal decomposition, in contrast to the carbon fibre reinforcement that does not degrade in nitrogen. In an air atmosphere, however, the CFRP and its constituents degrade via a complex reaction pathway encompassing three endothermic reactions (pyrolysis of the epoxy resin, oxidation of the residue from the first pyrolysis reaction and carbon fibre oxidation) that overlap and one endothermic reaction in nitrogen (pyrolysis of the epoxy resin). A deconvolution technique based on fitting log-normal distributions to the first derivative of the mass loss data has also been undertaken to separate the thermal decomposition reactions for each CFRP to understand the effect of each reaction's contribution. It can be used to evaluate complex thermal degradation processes that can be characterised by finding the respective kinetic parameters of each reaction, e.g. by using combined kinetics analysis.