A hybrid approach to carbon fiber recycling in epoxy composites

In this study, a novel two-step recycling technique combining thermal treatment and sodium chlorite-based chemical processing is proposed to reclaim carbon fibers from thermoset epoxy composites. A composite structure was manufactured employing vacuum-assisted resin transfer molding (VARTM). Then, the manufactured laminate was subjected to thermal treatment to partially degrade its epoxy matrix, resulting in delamination of the composite structure. Thermal treatment was performed at the minimum temperature required to separate carbon fibers without completely incinerating the epoxy matrix. The effect of the thermal treatment on the composite structure was detailed by monitoring its microstructure and weight loss via microcomputed X-ray tomography (μCT) and thermogravimetric analysis (TGA) tests. In the following step, the reclaimed carbon fiber layers were treated separately with a sodium chlorite-based oxidative chemical solution to promote the removal of thermally degraded epoxy residues and obtain clean recycled carbon fibers. Comprehensive experimental studies were conducted on the thermal treatment temperature and duration, and chemical recycling duration, to determine the optimum recycling conditions. As a final step, the recycled carbon fibers were extensively characterized by comparing their structural properties with those of the reference carbon fibers to assess the efficiency of the novel hybrid recycling technique applied. The characterization test results validate that carbon fibers with comparable structural and mechanical properties can be recovered by a hybrid recycling method under atmospheric pressure.