Electrochemical oxidation of carbon fibres: Surface chemistry and adhesion

PAN based carbon fibres were subjected to electrochemical oxidation under a wide variety of conditions. Sodium hydroxide, ammonium hydrogen carbonate, ammonium carbonate, sulphuric acid and nitric acid were used as electrolytes in four concentrations changing from 2 to 20 wt%. The applied voltage varied from 0.5 to 5 V in four steps. The surface chemistry of the fibres was studied by diffuse reflectance infrared spectroscopy (DRIFT). The strength of adhesion between the fibre and an epoxy matrix was characterised by the interfacial shear stress (IFSS), which was determined by fragmentation. The functional groups formed on the surface of the fibres depend very much on the type of the electrolyte used, while their number on its concentration, as well as on the voltage of oxidation. A close correlation was found between surface chemistry and fibre/matrix adhesion, the concentration of certain functional groups could be related quantitatively to IFSS. Some of the functional groups formed during oxidation could not be identified by the DRIFT technique used for analysis. (C) 2001 Elsevier Science Ltd. All rights reserved.