Derivation of Optimized Surface Treatment Method and Identification of Mechanisms to Improve the Interfacial Bonding Force between Waste Carbon Fibers and Polyamid-6

Abstract

To recycle waste carbon fibers (CFs) and use them as a composite material with polyamid-6 (PA-6), it is important to oxidize their surface without damaging it. However, it is unknown which of the surface treatment methods, such as acid, heat, and plasma treatments, is the most effective and what factors influence the effectiveness. In this study, waste CFs were subjected to nitric acid, heat, and plasma treatments under different conditions. Among the treatments, the amount of oxygen-containing functional groups (O-groups) such as lactone, which can increase the interfacial binding force with PA-6, was significantly increased by treating the fibers with nitric acid at 100 °C for 1 h without damaging the surface. Meanwhile, heat and plasma treatments introduced O-groups, but the surface was damaged. The introduction of O-groups increases the interaction force through hydrogen bonding between the oxygen in the O-groups and the hydrogen (N-H) in PA-6. Among the O-groups, the lactone was the most effective in the bonding reaction with PA-6. This supports that the nitric acid treatment was the best surface treatment with regard to the interfacial bonding force with PA-6. This precise derivation of the optimized surface treatment method lays a foundation for recycling CFs.

Keywords: waste carbon fibers, polyamid-6, Surface treatment, Interfacial shear strength, nitric acid treatment, lactone group