Properties of carbon/graphite fibers modified by plasma polymerization

Abstract Carbon fibers and pyrolytic graphite blocks were treated with plasma of acrylonitrile (AN) and styrene (ST) monomers, using an induction‐coupled, RF‐plasma reactor. Both substrates were stable towards plasma, leading to a deposition of thin, coherent coatings of 400Å∼1000Å thickness. Both monomers produced surfaces which are substantially more polar (γ_c=54 dynes/cm for AN and 40 dynes/cm for ST) than the untreated surfaces (γ_c=32 dynes/cm). ESCA and IR studies indicate that the plasma polymers contain a high concentration of oxygen (12 percent in PPAN and 17.8 percent in PPST), in the form of CO, COOH, COC, and OH groups. Also, treated fibers exhibited slightly higher tensile strengths than the untreated counterparts, suggesting that the plasma coatings effectively heal some of the surface flaws of the fiber. The abundant surface polar groups combined with the improved tensile properties of the plasma treated fibers make them attractive reinforcements for advanced composite materials.