Graphene Oxide based enhancement of electrical, thermal and mechanical properties of CFRP materials for wind turbine applications

The increasing use of carbon fibre reinforced polymers (CFRP) in weight critical structures have introduced new challenges associated with heat dissipation and electric current flow paths within the composite structure due to their anisotropic behaviour. The low transverse and in particular through-thickness electrical and thermal conductivities have been highlighted as the main parameters affecting the response of the laminates. Enhancing the properties in these directions is essential to enable the use of CFRP in aircraft, wind turbine blade and automotive applications and reduce the risk of damage. To establish a reference point, the anisotropic electrical and thermal behaviour of CFRP was experimentally quantified through self-developed measurement protocols. To enhance the electrical and thermal response of CFRP, commercially available graphene oxide (GO) nanoflakes were dispersed into the epoxy matrix studied considering two different case studies. In both cases the filler was added to the epoxy matrix prior being vacuum infused into dry carbon fabric to form CFRP laminates. Initially, the characterization of CFRPs containing randomly oriented GO showed that the electrical conductivity in the through-thickness direction increased markedly, reaching values up to 0.18 S/cm, when 6.3 vol% of GO was added into the epoxy, showing a threefold increase compared to the neat CFRP. Similar improvement was also found in the thermal through-thickness conductivity for the same filler content, where the laminate exhibited identical values in both transverse and through-thickness directions. However, the properties transverse to the fibres were not greatly affected by the GO addition. To assess the effect of the GO on the mechanical properties, interlaminar shear strength (ILSS) tests were conducted that showed that the addition of the GO significantly enhanced the through thickness shear strength, especially at low filler contents. In the second case study, an optimization of the previously developed laminates was realised aiming to lower the required GO filler content. By utilising an external alternating current (AC) field, the orientation of GO flakes was altered to take advantage of the higher electrical and thermal conductivity along the graphene basal planes. To assess the efficiency of the alignment method a comparison between laminates containing randomly oriented GO and aligned GO modified CFRP (A-GO/CFRP) laminates was realised. Measurements of the electrical conductivity revealed markedly increased values for the A-GO/CFRP even with low filler contents, validating the efficacy of the alignment. Further morphological characterization by means of scanning electron microscopy (SEM) revealed the formation of a chain-like conducting network interconnecting adjacent fibres. The thermal conductivity, albeit increased in A-GO/CFRP, only resulted in modest improvements. Mechanical tests of the ILSS showed that the A-GO/CFRP laminates exhibited significantly improved behaviour and retained higher ILSS values (than the randomly oriented GO CFRP laminates) even at high filler contents.