Hierarchical fibre reinforced nanocomposites for multifunctional improvements in safety

Certain nanomaterials, particularly carbon nanotubes (CNTs) and graphenes, offer the potential for fundamental improvements in mechanical performance and functional properties of composites. Individual nanocarbon structures have been shown to have a significantly higher strength than any other known materials (>50 GPa), combined with excellent stiffness, high lateral flexibility, high aspect ratio, and low weight; in addition, they have good electrical and thermal conductivities, and interesting optoelectronic characteristics, all relevant to (multi)functional performance. There is a large body of work on nanocarbon composites often showing useful improvements but at a relatively modest scale, based on the introduction of only very low loading fractions. Whilst assemblies based on pure nanocarbon constructs have demonstrated significant promise, creating a new class of strong macroscopic materials is challenging. In the nearer term, nanocarbons will have the biggest impact by enhancing the performance of existing state of the art carbon fibre composites, particularly by addressing critical matrix-dominated failures; current data are promising but are again limited to low loading fractions. In the contexts of both pure and hierarchical CNT composites, Imperial College has developed new processing methods that have the potential to deliver composites with high loading fractions of (functionalised) nanocarbons. The project will focus on these routes to deliver new high performance composite structures, combining reinforcements at multiple lengthscales. This hierarchical strategy is successfully pursed by nature, but here will be implemented using much higher performance components than are available under biological conditions. The introduction of the nanofiller into fibre reinforced polymer composites can help to address many of the current limitations of these other exceptional materials, particularly those related to safety. Matrix-dominated delamination tends to lead to premature and potentially catastrophic failures, which are hard to predict as the accumulation of damage is hard to detect. The introduction of nanofillers offers the opportunity to improve toughness and reduce damage sensitivity. In addition, the electrical conductivity of the system provides a means to monitor the growth of internal cracks at an early stage. Improvements in through thickness electrical conductivity at high loadings, may be sufficient to reduce dangerous field concentrations associated with lightning strike. In addition, the presence of high aspect ratio nanofillers has been shown to significantly improve fire resistance, by limiting oxygen diffusion and forming an insulating, stable char. The application of such effects within fibre composites offers a chance to resolve a major obstacle to composite implementation in many fields, particularly in shipping/offshore.

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