Influence of Hydrolysis Medium on Matrix Degradation and Carbon Fibre Recovery from Epoxy-Based CFRPs

The increasing use of carbon fibre-reinforced polymers (CFRPs) has intensified the need for efficient recycling technologies capable of recovering high-value carbon fibres from end-of-life composites. This study compares neutral and alkaline hydrolysis for recycling epoxy-based CFRPs under identical conditions (250 °C, 37-40 bar). CFRP waste generated during the manufacture of Formula Student race car components was treated in deionised water or 1.04 M NaOH for 60 or 120 min. Matrix degradation and fibre recovery were evaluated by gravimetric analysis, pH and conductivity measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Neutral hydrolysis resulted in only 4.5% mass loss and limited matrix degradation. In contrast, alkaline hydrolysis achieved mass losses of 34.2% and 38.7% after 60 and 120 min, respectively, with more extensive matrix removal observed after the longer treatment. Under strongly alkaline conditions, hydroxide ions can promote the cleavage of susceptible bonds within the epoxy network, facilitating matrix depolymerisation and removal. After 60 min, partial matrix removal was observed, whereas 120 min resulted in nearly complete matrix removal and successful carbon fibres recovery. FTIR, SEM, and XRD confirmed effective matrix removal while preserving fibre morphology and crystalline structure. The results demonstrate that alkaline hydrolysis is significantly more effective than neutral hydrolysis for recycling epoxy-based CFRPs and highlight the importance of combining complementary analytical techniques to reliably evaluate recycling efficiency.