THE SIGNIFICANCE OF THE FIBER COATING IN THE PRODUCTION OF CARBON-FIBER-REINFORCED CARBONS FROM HT CARBON-FIBERS AND PHENOLIC RESIN AS MATRIX PRECURSOR .2. PHENOLIC RESIN COATINGS

Commercially surface-treated HT carbon fibres were coated with phenoli c resin in order to reduce the adhesion of the phenolic resin matrix t o the fibre surface. Unidirectional (UD) composites were fabricated us ing uncoated and coated fibres and a standard phenolic resin as matrix ; the fibre volume fraction of the green composites was 60 vol%. The c omposites were carbonized at 1000 degrees C and treated at 2100 degree s C. The effect of the coating was examined by measuring mechanical pr operties and analyzing failure modes after curing, carbonization, and treatment at graphitization temperatures. The effectiveness of a pheno lic resin coating of optimum thickness was demonstrated by the flexura l strength after each processing step (values obtained without the coa ting are given in parentheses): after curing 2300 MPa (1000 MPa); afte r carbonization 400 MPa (260 MPa), after graphitization treatment 800 MPa (575 MPa).