Electrical and thermal conductivity in graphene-enhanced carbon-fibre/PEEK: The effect of interlayer loading

Abstract

Combining graphene at different loadings with composites offers the possibility of tailored electrical and thermal properties for the aerospace sector, including electrostatic dissipation, thermal management and lightning strike protection applications. The effects of interlaminar graphene loadings to impart property enhancement in fibre reinforced thermoplastic composites remains unknown. Spray deposition offers a highly scalable, and rapid method to embed graphene. This study investigates the application of spray-deposited graphene suspension synthesised via liquid phase exfoliation (LPE) to functionalise carbon fibre/polyether ether ketone (CF/PEEK) composites. LPE graphene suspensions were spray deposited onto CF/PEEK prepreg ply substrates to create smooth thin films. With increased deposition time the graphene thin film root mean squared roughness decreased from 3.51 μm to 2.52 μm. The addition of 0.25 wt%, 0.7 wt% and 1.1 wt% graphene to the interlaminar regions in consolidated CF/PEEK imparted enhanced electrical and thermal conductivity. Electrical conductivity enhancement of up to ∼252% transverse to the fibre direction and up to ∼204% through thickness was measured after the addition of 0.25 wt% graphene. Thermal diffusivity increased up to ∼183% through-thickness, while 61% in the transverse to the fibre direction with 0.7 wt% additions. However, increased graphene loading also increased the void content in the composite resulting in reduced shear strength. Excess surfactant vapourisation during high temperature processing likely created voids up to 2.8 vol% often located within the interply and interlaminar region hindering anisotropic conductivity enhancement. Nevertheless, graphene loadings within the interlaminar region show promise in imparting bulk property enhancement.