Basic surface oxides on carbon fibers Original Research Article

To influence the material properties of carbon fiber reinforced thermoplastics, basic carbon fiber surfaces were produced by heating fibers at 905°C under nitrogen, cooling to 25°C and exposing them to oxygen. Pure oxygen as well as air were used at different temperatures. Zeta (ζ)-potential (ζ=f(c, pH)) measurements confirmed the existence of basic surface functionalities on most of the carbon fibers investigated (high tensile (HT) and high modulus (HM) with the exception of ultra high tensile strength (UTS) carbon fiber). The obtained basic HT-carbon fibers were compared to thermally oxidized fibers (acidic character) of the same type, neglecting other methods for the preparation of acidic surfaces. Scanning electron microscopy micrographs revealed that the thermo-treated carbon fiber surfaces became slightly rougher. The basic carbon fibers obtained exhibited hydrophobic surfaces and a positive ζ-potential whereas acidic carbon fibers are hydrophilic and show a negative ζ-potential. The contact angles of basic carbon fibers measured by the modified Wilhelmy-technique versus water increase whereas they decrease versus diiodomethane. Solid surface tensions were calculated from the obtained contact angle values.