Characterization of carbon fibers recovered from 3D woven CFRPs via pyrolysis and solvolysis

Recycling carbon fiber reinforced polymers (CFRPs) is essential to address the growing waste generated by their increased use in industries such as aerospace, automotive, and wind energy. This study compares two recycling methods, pyrolysis (with and without oxidation) and solvolysis, for the recovery of carbon fibers from a 3D woven CFRP. Pyrolysis experiments were conducted at 500°C for 2 and 6 h, followed by oxidation at different durations. A mass balance approach was employed to monitor material transformations, quantifying outputs including syngas, char, hydrocarbons, and recovered carbon fibers. Solvolysis experiments were carried out using supercritical water under different conditions of temperature, pressure, and reaction time. The efficiency of resin decomposition was assessed, while the morphological characteristics and mechanical properties of the recycled fibers were characterized for both processes using scanning electron microscopy (SEM) and single fiber tensile testing. Scanning electron microscopy (SEM) and mechanical tests were conducted for both processes to characterize the purity and performance of the recycled fibers. The results showed that pyrolysis followed by oxidation achieved high resin removal efficiency, with the optimal balance for fiber degradation, process control, and industrial costs being achieved with 2 h of pyrolysis followed by 30 min of oxidation. Under these conditions, the mechanical degradation of recycled fibers was limited to approximately 10% of the virgin fiber tensile strength. Solvolysis performed at 390°C, 265 bar, for 60 min also demonstrated effective resin removal while maintaining satisfactory mechanical properties of the recovered fibers.