Recovery of carbon fiber from prepreg using nitric acid and evaluation of recycled CFRP

Due to the strong demand for high specific strength materials in society, the production volume of CFRP is rapidly increasing, while the CFRP waste is simultaneously causing many problems. Despite many studies focusing on the recovery of carbon fiber from these wastes, the problem of reducing its mechanical strength remains. In this study, nitric acid decomposition was employed to recover the carbon fiber from CFRP prepreg. First, several oxidants including nitric acid were compared to verify which solvent was the most effective in the resin decomposition. We found that nitric acid was the best in recovering carbon fiber from prepreg. Then, the recovery of carbon fibers was scaled-up to obtain enough amount to fabricate recycled CFRP. The resin was efficiently removed by using nitric acid at 80 °C for 30 min. Several analyses also confirmed that no significant damage was induced to recovered fibers. Especially, regardless of losing a sizing agent on the fiber through the nitric acid decomposition, the interfacial shear strength of the recovered fibers was almost the same as virgin fiber since nitro and amino groups added to the carbon fiber surface reinforced the adhesiveness between the fiber and the resin. Finally, recycled CFRP fabricated from the recovered fibers showed comparable tensile properties with virgin CFRP, indicating that nitric acid decomposition method is a practical and promising method to recycle carbon fibers. This is the first study encompassing the nitric acid decomposition of CFRP prepreg, the detailed analyses of recovered fibers, and the production of the recycled CFRP.