Mixed Surface Chemistry on Carbon Fibers to Promote Adhesion in Epoxy and PMMA Polymers

Carbon fibers were surface modified using mixed grafting solutions of methyl methacrylate and glycidyl (epoxy) methacrylate in ratios of 0:100; 25:75; 50:50; 75:25; and 100:0, respectively. When evaluated in an epoxy resin, all modified fibers showed significant improvement in fiber-to-matrix adhesion. Notably, the surface-grafted polymer with blends of methyl methacrylate:glycidyl methacrylate of 0:100 and 25:75, respectively, showed a >200% improvement in adhesion relative to control fibers. When evaluated in PMMA, again significant adhesion improvements were observed, though fibers grafted with ≥25% methyl methacrylate were statistically indistinguishable. This shows that by correctly tuning the surface chemistry an optimal covalent sizing can be developed for thermoplastic and thermoset resins. As an additional benefit, a significant improvement in the treated fiber's tensile strength and modulus was also observed.