Synergetic surface modification of 3D braided carbon fiber-reinforced composites for enhancing mechanical strength

Excellent interfacial bonding contributes to the reduction of internal defects in composites for enhancing the mechanical properties of the 3D braided carbon fiber reinforced composites. In this paper, the effects of plasma and strong acid treatment on the surface morphology, chemical composition, and surface free energy of original carbon fiber braid (CFB) were investigated in detail to reveal the mechanism of synergetic enhancement of surface wettability of carbon fiber by plasma and strong acid. The results showed that the synergetic effect of plasma and strong acid produced significantly improved the resin/fiber interfacial bonding. The interfacial shear strength (IFSS) of the carbon fiber braided reinforced composites (CFBC) treated with the synergetic treatment was 64.6% higher than that of the untreated fiber reinforced composites. The improved interfacial properties increase the polar functional groups on the fiber surface to promote the formation of mechanical interlocking caused by Cassie-Baxter(CB) and Wenzel(WZ) leaps of liquid resin on the fiber surface, and this was verified by molecular dynamics(MD) simulations of carbon fiber-resin interfacial wetting. The simple and effective synergetic reinforcement strategy proposed in this paper can effectively regulate the interfacial bonding and is applicable to the optimal design of original carbon fiber braided reinforced composites.