Electrochemical surface modification of carbon fibres by grafting of amine, carboxylic and lipophilic amide groups

The surface of carbon fibre was rapidly modified by reductive electrochemical deposition employing a range of diazonium salts. Three sets of fibre were generated possessing pendant amine, carboxylic acid, and lipophilic amide (N-hexyl amide) groups and the effect of these surface chemistries on interfacial shear strength (IFSS) was examined in epoxy resins. Surface grafting of the fibres was studied by X-ray photoelectron spectroscopy, and physical characterisation of the modified fibres showed that our treatments had no detrimental effects on Young's modulus and tensile strength. IFSS increases of 172% and 30% (relative to control fibres) were observed for the amine and lipophilic amide functionalised, respectively. Molecular dynamics simulations of the lipophilic amide suggests IFSS enhancement via soft-soft interactions. Surprisingly, the IFSS of fibres that exhibited carboxylic acid groups at the surface were indistinguishable from that of the untreated control fibres. When applied to polypropylene grafted with maleic anhydride, the amine grafted fibres showed a 67% increase relative to control fibres, attributed to covalent cross-linking between the fibre and maleic anhydride co-monomer.