The creation of carbon composite with specific kinds of enhanced functionality are needed for applications in engineering, and especially in the aerospace industry. Conventional CFRP has relatively poor electrical and thermal conductivities as a consequence of the encapsulating insulating polymer matrix. Moreover, CFRP is inherently non-isotropic within its properties, (specifically, mechanical, electrical and thermal conductivities). For that reason, the in-plane properties from the CFRP are covered with the high strength, stiff, electrically and thermally conductive fibres whilst the out-of-plane properties are dominated by the low strength, ductile, electrically and thermally insulating polymer matrix. Even though the in-plane electrical and thermal conductivities are higher than the out-of-plane directions, they are still relatively poor and may limit the uses of the information. Subsequently, it is actually of particular interest to impart electrical and thermal functionalities within the in-plane as well as the out-of-plane directions of the carbon fibre composites.
The aerospace industry is a good example of a marketplace that could benefit from electrical conductivity enhancements. Lightning strike protection for CFRP currently depends on metallic structures, typically such as metallic foils that happen to be on the upper surface on the CFRP laminate. These metallic structures are comparatively heavy and introduce manufacturing difficulties. Additionally, the contrasting mechanical properties of your metal and the composite introduce additional stresses, weakening the structure. Because of this, it really is useful to develop a different carbon-based conducting composite, enabling removing metals within these structures.
The poor thermal conductivities from the CFRP composites present issues for that aerospace industry when de-icing in the structures, along with any dimensional instability in space structures that utilise these elements. Current solutions, like bleeding heat from your jet engine or melting/preventing ice through electric circuits (via Joule heating) depend upon conduction/convection mechanisms. The inherent poor thermal conductivity of CFRP renders these solutions energy/cost inefficient. Furthermore, CFRP structures will not be as capable as aluminium in minimising fuel temperatures during cruising altitudes – creating the chance of inadvertently forming explosive vapours. Subsequently, to enhance the efficiency of current de-icing solutions and minimise fuel vapour formation, there is a need to increase the thermal conductivity of the CFRP composites.
One promising area is utilising carbon nanotubes (CNTs) – hexagonal arrays of carbon atoms rolled in to a seamless tube. They possess the ideal properties: high tensile strength (greater than carbon fibres1), high Young’s modulus2,3 and electrical and thermal conductivities4, imparted in the strong sigma bonds between the in-plane carbon atoms along with the sp2 hybridisation. Moreover, they can be attached to, or grown around the carbon fibres (called – fuzzy fibres)5,6. Grown or attached, CNTs are certainly not expected to be distributed in to a polymer matrix (where harmful functionalisation to the CNTs is essential) and so they will not improve the viscosity of your polymer matrix to the detriment from the processing of the composite4,7,8,9,10.
There is a preference in the research community to cultivate the CNTs as opposed to attaching them11, as the quality, quantity, controllability of size12 and alignment of the CNTs are superior. The disadvantages of growing CNTs may be the decrease in the mechanical properties of your underlying carbon fibres when conventional growth techniques are used13. Previously, we reported an image-thermal chemical vapour deposition (PT-CVD) growth system for CNTs on carbon fibres where just a 9.7% decrease in tensile performance was recorded5. However, the increase temperatures encountered inside the PT-CVD system still exceeds the melting point of the polymer sizing5. It is a ~1?wt. % addition of your proprietary polymer (typically an epoxy of low molecular weight), placed on the surface of the carbon fibres to help handling14, enhance the interfacial adhesion between fibre and matrix14,15 and permit the polymer matrix to wet-out your carbon fibres16,17.
In this particular work, we demonstrate that CNTs give you the necessary functionality for that aerospace industry, whilst replacing the polymer sizing typically put on carbon fibres. The examination of the physical and mechanical properties in the CNTs as an alternative for your polymer sizing are presented elsewhere18. To summarise, following fibre volume fraction normalisation, enhancements of: 146% inside the Young’s modulus; 20% from the ultimate shear stress; 74% in shear chord modulus and 83% in the initial fracture toughness were observed18.
The CNTs are grown while using PT-CVD and the resulting high density and quality of CNTs has led – with no polymer sizing – for the retention of the mechanical integrity in the carbon fibre fabric dexnpky63 the composite fabrication capability. Furthermore, the density, quality of CNTs and length of CNTs has vastly improved the amount of electrical and thermal percolation pathways, resulting in significant improvements with their properties. The fabrication in the composites (fuzzy fibre and reference samples) were implemented having an industrially relevant vacuum assisted resin transfer moulding (VARTM) process. Additional samples were produced where merely the uppermost plies are modified, in analogy on the metal-foil structures currently useful for lightning strike protection.
Therefore, the solution presented herein, is really a direct “all-carbon” alternative to the polymer sizing that moreover provides electrical and thermal functionality ultimately showing that it approach not only provides a viable alternative for current metal-foil containing CFRP, but opens with other industries and applications.