Electrodeposition of a polymer interphase in carbon‐fiber composites

Abstract The performance of an electrodeposited interphase of poly(butadiene‐co‐maleic anhydride) (BMA) in carbon‐fiber composites is investigated. Carbon fibers are electrocoated with BMA from an aqueous solution and the coated fibers are fabricated into composite bars for evaluation of mechanical properties. These composites show superior impact strength, but lower interlaminar shear strength, compared to composites made from commercially treated fibers. It is suggested that unsaturation in the butadiene segments of the interphase polymer leads to the formation of a crosslinked layer during electrodeposition and subsequent drying. Inadequate penetration of this interphase by bulky epoxy molecules leads to a weak interphase/matrix interface which is the locus of failure, generating the observed mechanical properties. These conclusions are supported by examination of the fracture surfaces by Scanning Electron Microscopy. Further evidence of lack of matrix penetration into the interphase comes from electron microprobe line scans for bromine performed on cross‐sections of single‐filament composites, the bromine being introduced into the matrix via a brominated epoxy resin. Appropriate control of the chemical structure and physical characteristics of the interphase polymer is thus indicated, for acieving simultaneous improvements in impact and interlaminar shear strengths.