Interface molecular engineering of carbon-fiber composites

Adhesion of carbon fibers to epoxy and related resins is a complex subject requiring a fundamental understanding of: (a) the nature of the adhesive ch aracteristics of the fiber; (b) the mechanisms involved; and (c) an appropr iate quantification of adhesion. This paper discusses the application of pl asma co-polymerization of acrylic acid/hexane, allyl alcohol/hexane and all ylamine/octadiene, for the controlled functionalization of untreated type i i carbon fiber through the deposition of thin, conformal coatings. The sing le-fiber fragmentation test has been used to estimate the influence of thes e pretreatments. The conventional data reduction technique and cumulative s tress transfer function (CSTF) have been used as a measure of adhesion. The surface free energy of the coatings of allyl alcohol/octadiene deposited o n glass plates, has also been estimated from the contact angle of polar and non-polar liquids. Hydrocarbon coatings resulted in a lower degree of adhe sion than the parent untreated fiber. Increasing the concentrations of acry lic acid and allylamine promoted adhesion. This was attributed to the forma tion of covalent bonds between functional groups on the fibers and epoxy gr oups. The incorporation of allyl alcohol was less effective, because only d ipole-dipole interactions were available. Contact angle measurements indica ted that the polar component of surface free energy increased with the hydr oxyl group concentration, despite no quantifiable increase in adhesion. The CSTF methodology has been shown to provide a precise estimate of adhesion. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.