Analyses of reinforcing effects of in situ grown CNTs on carbon fibre fabric/epoxy composites at micro- and macroscale

Carbon nanotubes (CNTs) have been in situ grown on the surface of carbon fibre fabric (CFF) by electrochemical oxidation, urea hydrolysis and chemical vapour deposition process. The reinforcing efficiency of the in situ grown CNTs (I-CNTs) was analysed at micro- and macroscale by atomic force microscopy (AFM), single fibre pull out tests and mechanical properties of I-CNTs reinforced CFF/epoxy composites. AFM analyses indicated that the bonding strength between a single piece of I-CNTs and carbon fibre (CF) was ~50~700~nN, which was much higher than that between CF and CNTs on the surface of CF adsorbed in CNTs suspension. Further investigation of single fibre pull out tests showed that the interfacial bonding strength between CF with I-CNTs and epoxy resin was 39~ higher than that between pristine CF and epoxy resin. Correspondingly, the bending strength and interlaminar shear strength of I-CNTs/CFF/epoxy were 26 and 52~ higher than those without reinforcement of I-CNTs. The significant improvement could be ascribed to the high strength of uniformly dispersed I-CNTs themselves, high bonding force between I-CNTs and CF, and improved interfacial bonding strength between the reinforcers and matrix.