Mechanical properties of carbon fibers and fiber/matrix interface recycled from CFRPs via water/ethanol-based solvolysis under various processing conditions

A novel solvolysis approach for recovering carbon fibers from CFRPs using water/ethanol solvent is introduced. Experiments were conducted under varying solvent volume ratio, temperature, and reaction time. The design of experiments methodology was employed to systematically evaluate the influence of these parameters on resin decomposition efficiency (RDE), fiber morphology, and the mechanical and interfacial properties of the recycled carbon fibers (rCFs). Additionally, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method was applied to rank experimental conditions based on a performance index. To characterize the rCFs, single-fiber tension tests, microbond tests, and SEM analyses were performed. RDE efficiency ranged from 35–68% at 320 °C and increased to 75–92.5% at 350 °C and 380 °C. Tension tests showed that rCFs recovered under optimal conditions retained tensile strength and Young’s modulus. In contrast, residual resin or surface damage led to mechanical property degradation of up to 30%. Microbond tests revealed a wide variation in interfacial shear strength: while some rCFs maintained near-virgin values, others experienced reductions of 17% to 48%. The combined retention analysis of mechanical properties and TOPSIS evaluation identified the most favorable recycling condition as the treatment at 380 °C for 90 min using pure water as the solvent.