One of the major challenges in the field of nanocomposites has been to distribute and disperse high loading fractions of carbon nanotubes (CNT) in epoxy resins through a route that is scalable to high throughput. Furthermore, CNTs have been employed as an additional constituent in advanced carbon fibre composite materials to improve their poor matrix dominated properties in the drive to manufacture lighter and stronger composite structures. Attempts to produce epoxy based hierarchical composites (HC) with high CNT loadings by introducing nanoreinforcement in the resin have been plagued by processing difficulties related to viscosity and infiltration.
Nonetheless, introducing just a few weight percent of CNTs into the matrix of continuous carbon fibre composites has been shown to enhance fracture toughness and compression performance. As such, this thesis tackles an effective way to combine carbon fibre, thermosetting resin and CNTs into hierarchical composites with high loadings of nanoreinforcement. To this end, a readily scalable powder based processing route was developed to produce epoxy based polymer nanocomposites (PNC) with a maximum CNT loading of 18.4 wt% (11.5 vol%). Due to the excellent CNT distribution and dispersion achieved during processing, some practically relevant physical and mechanical properties were enhanced even at the highest CNT loadings: 67 S/m and 0.77 W/ m•K electrical and thermal conductivities, respectively, and 5.5 GPa Young’s modulus. Analytical micromechanical models to validate reinforcement due to CNTs were also explored.
The nanocomposite powder was also employed as a constituent in a wet powder impregnation process to produce carbon fibre based HC laminates containing as much as 5.5 vol% CNTs (11.5 vol% CNTs in the matrix). The processing parameters were optimised to yield a laminate with 55% fibre volume fraction, making it suitable for structural applications. The through thickness electrical conductivity of the HC containing 5.5 vol% CNTs improved by an order of magnitude; however, the largest enhancement in interlaminar fracture toughness (20%) was observed at an intermediate loading of 2 vol% CNTs. The mechanical underperformance at high CNT loadings was attributed to the heterogeneous microstructure observed to different extents in both PNCs and HCs, and a number of solutions related to material selection and processing design were proposed.