Effect of coupling treatment of carbon fiber surface on mechanical properties of carbon fiber reinforced carbon composites

Unidirectional carbon fiber reinforced carbon composites (C/C composites) were Prepared from a high modulus-type carbon fiber, treated with either silane or titanate coupling agents, and a furanic resin matrix precursor. Regardless of coupling treatments of fibers, a preferentially oriented region parallel to the fiber surface was observed at the interphase in the carbon matrix derived from furanic resin. The matrix interphase was flattened by development of graphitic structure after heat treatment at 2600 degrees C. In the composite fabricated from untreated fiber, the strong adhesion between fiber and matrix resulted in damage of the reinforcing fibers by the flattening of the matrix. The coupling treatments weakened the interfacial adhesion between carbon fiber and carbon matrix, and prevented fiber damage resulting from matrix flattening by separation at the interface. In the graphitized composite fabricated from silane coupling-treated fibers, the interfacial adhesion became so weak that fiber pull out was observed on fracture. The titanate coupling treatment limited the extent of graphitization of matrix in the composite. For composites fabricated from titanate coupling-treated fiber, the tensile strength increased with increasing heat treatment temperature. The graphitized composites from titanate coupling-treated fibers showed 50% higher strength than the composite from untreated fibers. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.