X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES OF CARBON-FIBER SURFACES .18. INTERFACIAL INTERACTIONS BETWEEN PHENOLIC RESIN AND CARBON-FIBER ELECTROCHEMICALLY OXIDIZED IN AMMONIUM CARBONATE SOLUTION AND THEIR EFFECT ON OXIDATION BEHAVIOR

The interfacial interactions between a carbon fiber electrochemically oxidized in ammonium carbonate solution and a phenolic resin were inve stigated by core and valence-band X-ray photoelectron spectroscopic st udies (XPS) of a very thin resin layer on the surface of the fiber. Th e work continues a study related to the need to improve the oxidation stability of carbon-carbon composites by an investigation of this firs t step in their formation and the possibility of preferential oxidatio n at the fiber-matrix interface. The interaction between the surface t reated fiber and the resin was investigated, together with the effect that several different coupling agents had on this interaction. Valenc e band XPS, interpreted by spectra generated by ab initio molecular or bital calculations based upon particular chemical interaction models, proved valuable in understanding the nature of this chemical interacti on. Model calculations suggested that the most likely chemical linkage is an ether linkage formed directly between the oxidized fiber and th e resin and that the use of glutaraldehyde as a coupling agent led to probable hemiacetal cross-linking between the oxidized fiber and the r esin. The effect of air oxidation on the resin coated fibers (with or without coupling agents and fiber surface treatment) was examined by t hermogravimetric analysis. The results show that improved oxidation be havior can be achieved in eases where interfacial chemical reaction oc curred between the resin and fiber.