Covalent sizing surface modification as a route to improved interfacial adhesion in carbon fibre-epoxy composites

The polymerisation and attachment of a covalent sizing to the surface of carbon fibres is demonstrated using an electrochemical surface treatment. This treatment proceeds in an aqueous environment at a constant potential of −1 V in 2 min, and thus is within the window of current industrial surface treatments (2–4 min). This treatment demonstrates the ability to significantly increase the tensile strength (up to 25%), Young’s modulus (up to 15%) and interfacial shear strength (IFSS, up to 199%) in an epoxy resin. Optimisation of this process gave similar improvements in carbon fibre properties and IFSS at lower monomer concentrations (0.2 M and 0.5 M vs 1.0 M). This treatment is demonstrated on both bundles of fibres and woven fabrics and the woven fabrics are able to be reversibly moulded into different shapes by simply wetting the surface with an appropriate solvent and allowing to dry.