INFLUENCE OF ELECTROCHEMICAL TREATMENT ON THE SURFACE-PROPERTIES OF CARBON-FIBERS - ACID-BASE CHARACTER AND ADSORPTION ENTHALPY

High strength carbon fibers (SOFICAR, T-300, 3K fibers), were electrochemically treated in an aqueous sodium hydroxide solution, at increasing current densities, using an original continuous treatment process. The electrochemical treatment induced a modification of the surface properties, i.e. acid-base character and adsorption enthalpy of gaseous probes, as measured by inverse gas chromatography (IGC) at infinite dilution. Our results show that the: use of weak acidic probes (CCl4-chloroform) of Gutmann is not adequate for the determination of the acid-base character of a solid surface. Firstly, it appears that all studied carbon fiber surfaces have an amphoteric character, becoming more basic in our experimental treatment conditions. When the current intensity of the electrochemical treatment increases, both surface acidity and basicity increase, in the interval of about 90-300mA. However, no significant changes in the acid-base characters are observed for strong treatment (>300mA). Hence, a moderate treatment (90mA) is sufficient to obtain optimum acid-base properties. This treatment is possibly suitable for carbon fibers to be incorporated in polar organic matrices and will lead to efficient fiber-resin bonding.