Basic surface oxides on carbon fibers

To influence the material properties of carbon fiber reinforced thermoplast ics, basic carbon fiber surfaces were produced by heating fibers at 905 deg rees C under nitrogen, cooling to 25 degrees C and exposing them to oxygen. Pure oxygen as well as air were used at different temperatures. Zeta (zeta )-potential (zeta = f(c, pH)) measurements confirmed the existence of basic surface functionalities on most of the carbon fibers investigated (high te nsile (HT) and high modulus (HM) with the exception of ultra high tensile s trength (UTS) carbon fiber). The obtained basic MT-carbon fibers were compa red to thermally oxidized fibers (acidic character) of the same type, negle cting other methods for the preparation of acidic surfaces. Scanning electr on microscopy micrographs revealed that the thermo-treated carbon fiber sur faces became slightly rougher. The basic carbon fibers obtained exhibited h ydrophobic surfaces and a positive zeta-potential whereas acidic carbon fib ers are hydrophilic and show a negative zeta-potential. The contact angles of basic carbon fibers measured by the modified Wilhelmy-technique versus w ater increase whereas they decrease versus diiodomethane. Solid surface ten sions were calculated from the obtained contact angle values. (C) 1999 Else vier Science Ltd. All rights reserved.