Chemical Recycling of CFRP in an Environmentally Friendly Approach

A novel and environmentally friendly recycling approach for carbon-fiber-reinforced plastics (CFRP) was studied using not only nitric acid (HNO₃) but also our chosen alkaline, sodium hydrogen carbonate (NaHCO₃). The CFRP specimen was first immersed into 8 M HNO₃ at 80 °C for 8 h, and then into 0.1 M NaHCO₃ at 80 °C for 15 min to obtain resin-free recycled carbon fiber (rCFs). Using this new recycling method, it was shown that the recycling time was reduced to 8.3 h, whereas it originally took 24 h, as reported previously. It was shown that immersing the CFRP specimen into NaHCO₃ caused a transesterification reaction with the remaining resin residue on the CF surface, which led to dissolving the resin into the NaHCO₃ aqueous solution all at once. Additionally, NaHCO₃ produced carbon dioxide gas while reacting with the resin residue; the CO₂ gas physically helped removing the resin from the CF's surface. Moreover, evaluating the physical properties of the rCFs demonstrated an improvement in fiber strength and adhesiveness to resin. Therefore, this recycling method was shown to be effective in recovering high-quality rCFs in a relatively short recycling period.