Improved Mechanical Properties of Graphene/Carbon Fibre Composites via Silanization

Despite their excellent mechanical performance, carbon fibre reinforced polymer (CFRP) composites are limited by the interfacial properties due to the inherent nature of laminated structures. One way to modify the interface is by the inclusion of nanomaterials on the surface of carbon fibres. Here, we use electrochemical exfoliation to produce graphene (EEG) flakes which have hydroxyl and epoxy functional groups on their surface. To further improve the interfacial bonding between the flakes and the epoxy matrix, silanization was carried out on the graphene, with 3-aminopropyl triethoxysilane (APTES) which could react with both oxygen and amino groups, and then EEA flakes achieved. Combing SEM and AFM, lateral size and thickness of both flakes were characterized, which showed comparable values, and thus removed the effect of aspect ratio during the comparison. Both EEG and EEA flakes were dispersed in ethanol and sprayed coated onto carbon fibres, followed by vacuum assisted resin infusion to make hybrid composites. Testing of their mechanical properties showed that EEG flakes tend to act as points of stress concentration which accelerated the delamination; while the EEA flakes improved interfacial properties owing to the covalent bonding. As a result, with only 0.5 wt.% EEA flakes spray coated onto the carbon fibres, the tensile and flexural strength of graphene/carbon fibre composites improved by 17.6% and 5.4% respectively.