Influence of thermal treatment on the properties of carbon fiber reinforced plastics under various conditions

Thermal treatment has been regarded as an effective method for recycling carbon fiber reinforced plastics (CFRP). In this paper, the influences of operating temperature, oxygen concentration and superheated steam on the thermal behaviors of virgin carbon fibers (CF) and CFRP were investigated. The properties of recycled CF (rCF) were determined by yarns tensile test, SEM and Raman analyses. The TG results suggested that the oxidation of CFRP was comprised mainly of the decomposition and the oxidation of epoxy matrix, the oxidation of pyrolytic residue, and the oxidation of CF. For the virgin CF, temperature showed a negligible effect on the tensile strength of CF in N₂ atmosphere, whereas the injection of oxygen or superheated steam greatly reduced their tensile strength with the increasing temperatures. Higher temperatures led to the surface defects of treated CF due to the oxidative effect. An amount of pyrolytic residue was observed on the rCF during the CFRP pyrolysis. Increasing the O₂ concentration removed the pyrolytic residue from the rCF at 500 °C, preserving 94% of the original tensile strength. Higher temperatures showed negative effects on the properties of rCF, where the surface defects were clearly observed, and were exacerbated with higher O₂ concentrations. Superheated steam could remove the pyrolytic residue and preserved the properties of rCF.