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 electrolyt
es in four concentrations changing from 2 to 20 wt%. The applied voltage va
ried 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. Th
e 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 betw
een surface chemistry and fibre/matrix adhesion, the concentration of certa
in functional groups could be related quantitatively to IFSS. Some of the f
unctional groups formed during oxidation could not be identified by the DRI
FT technique used for analysis. (C) 2001 Elsevier Science Ltd. All rights r
eserved.