Solvothermal degradation of carbon fibre-reinforced epoxy resin composites

Carbon fibre-reinforced epoxy resin composites (CF/EP) have been widely used in the shipping, aerospace and construction industries due to their excellent corrosion resistance and mechanical properties. However, thermosetting resins form insolubility and non-melting three-dimensional cross-linked networks after curing, making these materials difficult to be recycled. In our research described in this paper, we propose a solvothermal degradation method for recycling carbon fibres from CF/EP. We utilised acetic acid and hydrogen peroxide as solvents and controlled the reaction conditions at 100°C–130°C for 90 min–180 min to degrade CF/EP in a Teflon-lined autoclave. The experimental results indicated that the degradation degree of resin gradually increased with the reaction temperature and reaction time, reaching up to 99.8% at 100°C for 180 min. Based on scanning electron microscopy, X-ray diffraction, Raman spectra analyses and X-ray photoelectron spectroscopy, we observed that the surface of the recycled carbon fibres had almost no resin residue and their microstructure was not significantly changed. The monofilament tensile strength of the recycled carbon fibres was 3.48 GPa. The strength retention rate of the RCF-100°C-180 min was as high as 99.15% relative to the virgin carbon fibres, further confirming that the solvothermal degradation process hardly damaged the mechanical properties of the recycled carbon fibres. In addition, a possible degradation mechanism of CF/EP was proposed based on Fourier transform infrared spectroscopy analysis. The epoxy resin was efficiently degraded under the dissolution/swelling effect and chemical degradation reactions.