Plasma polymerisation for molecular engineering of carbon-fibre surfaces for optimised composites

This paper explores the relationship between fibre surface chemistry and interfacial bond formation in carbon-fibre/epoxy composites. Plasma copolymerisation of acrylic-acid/hexane, allyl-alcohol/hexane and allylamine/octadiene gas mixtures is used to obtain molecularly thin, conformai coatings on Type A carbon-fibre surfaces. Since the microporosity and chemical functionality of the untreated fibre surface can be concealed, any functionality incorporated into the film can be considered to provide the principal adhesion mechanism. The single-filament fragmentation test has been employed to estimate the adhesion of these modified fibres to an epoxy resin. Coatings of a hydrocarbon nature inhibit chemical interaction between the fibre and matrix. Improvements in the level of adhesion may be attributed to the introduction of oxygen- and nitrogen-containing functionalities which have known reactivity to epoxy groups. Thus, carboxylic acid and amine groups are shown to be more effective than hydroxyl groups.