Improved amine functionalization of carbon fiber surfaces by O2 plasma activation treatment

Pretreatment using O2 plasma is a commonly used method today to increase the surface activity of CFs and enable more functional groups to be grafted onto them. Although the oxidation treatment of the CF surface is considered a key procedure for further grafting with functional groups, few researchers have investigated how the oxidation treatment influences the grafting processes. In this paper, the effects of the degree of oxidation on the grafting of amino functional groups onto CFs were experimentally investigated. The experiment showed that the oxidation process developed in steps including initial oxidation, saturation oxidation, and peroxidation. The results demonstrated that the degree of oxidation was positively correlated with the grafting efficiency within a certain range. Furthermore, the groups (unsaturated C, C-OH, and O=C-OH) produced after oxidation determined the results of grafting with amino (C-N, C-NH2, and O=C-NH2) groups. When the O2 plasma treatment time was increased from 0 min to 3 min, the IFSS of CF@HA increased by 1.07 times and the flexural strength of CFRP increased by 1.26 times. This work proves that the ammonia grafting of CF can be controlled by adjusting its earlier oxidation process.