Interfacial debonding strength between the edge surfaces of pyrolytic graphite and epoxy resins

Abstract

The edge surfaces of pyrolytic graphite have been treated by anodic oxidation and the interfacial debonding strength (IFDS) between the oxidized edge surfaces and epoxy resin measured. The unoxidized and oxidized edge surfaces were examined by X-ray photoelectron spectroscopy. The edge and epoxy resin surfaces after debonding test were examined by a field-emission scanning electron microscope. Carboxyl groups were expected to be added in great quantities by breaking the carbon-carbon bonds at the edge surface. On the other hand, hydroxyl groups could be added to edge carbon atoms at the edge surface without breaking the carbon-carbon bonds. The rise in IFDS with anodic oxidation does not correspond directly to the O/C ratios or the amount of carboxyl groups present on the edge surface. Hydroxyl groups added to the edge surface are considered to play an important role in improving the adhesion between the edge surface and epoxy resin through covalent bonds between hydroxyl and epoxy groups. In the case of epoxy resin used in this study, IFDS initially increased to 9 MPa with increasing -OH/C ratio up to about 0.02; thereafter it remains constant at this value. This strength is lower than those of PG and epoxy resin.