Recovery of carbon fibers from aviation epoxy composites by acid solvolysis

Abstract

Aircraft industries produce massive quantities of carbon fiber reinforced polymers which must be recycled to comply with the directives of the circular economy. In this context, carbon fiber of reinforced epoxy resin composites from the aircraft construction industry were recovered by nitric acid-catalyzed hydrolysis at 95 °C. The operating conditions, such as the concentration of nitric acid, the weight ratio composite/solution, and the number of cycles of the ultraviolet treatment (UVB) irradiation were studied. UVB was used to induce the polymer degradation and thus decrease the severity of the hydrolysis process. The UVB treatments were performed in a weathering chamber at 60 °C. The reclaimed carbon fibers and virgin carbon fibers, used as standard, were characterized by X-ray diffraction, Raman spectroscopy, thermogravimetry under airflow, and scanning electron microscopy (SEM). As expected, UVB irradiation was able to initiate the polymer degradation process which was beneficial for the overall recycling process. Data from characterization techniques showed that the UVB irradiation caused some damage to carbon fibers. Without irradiation pre-treatment, the collected fibers showed characteristics like those of virgin fibers with a slight decrease in thermal stability which can arise from surface oxidation. The tensile strength of recovered fibers was sensitive to nitric acid concentration during hydrolysis because long contact time with acidic solutions causes oxidation of CF. Optimization of nitric acid concentration and hydrolysis step duration must be carried out to minimize CF surface oxidation.