Nitric acid oxidation of carbon fibers and the effects of subsequent treatment in refluxing aqueous NaOH

Nitric acid oxidation effectively created acidic functional groups on PAN-based high-strength carbon fibers. The acidic capacities of carbon fibers increased with oxidation time. Typically, 60 minutes of oxidation created 60 μeq acidic functional groups on each gram of carbon fibers. Nitric acid oxidation also caused tensile strength decreases and fiber weight losses. By treating fibers in refluxing aqueous NaOH after nitric acid oxidation, a weakly bound layer of partially oxidized graphitic fragments was removed and this caused higher weight losses. This treatment also removed a source of interference in later analyses. The effects of aqueous NaOH treatment after oxidation on the mechanical properties (tensile strength, Izod IS, IFSS, and ILSS) of fibers and their composites were also investigated.