Wettability of Nitric Acid Oxidized Carbon Fibers

High-strength carbon fibers were oxidized by exposure to nitric acid and single-fiber wettability predictions were compared to the actual wettability of multiple fibers in resin. Single-fiber wettability was predicted through contact-angle measurements and surface-energy calculations. Multiple-fiber wettability in resin was evaluated by immersing treated fiber bundles in catalyzed vinyl ester resin, followed by cross-sectional viewing after curing. Fiber cohesion, macro-composite void content, and transverse tensile strength were also examined as a function of fiber treatment time. Fiber surface energy increased with treatment time, suggesting improved wettability. However, fiber cohesion also increased and composite wetting was found to suffer. Increasing fiber treatment times resulted in larger unwetted areas, higher void content, and declining transverse tensile strength.