Fabrication of Carbon Nanotubes-Doped Veils

Abstract

Non-woven fabrics (veils) are structural materials consisting of randomly arranged thin fibres. They are used as an interlayer in the laminate fabrication process to improve mechanical properties of composites, especially their fracture toughness. A new role of such veils could be the enhancement of the electrical conductivity of laminate. For this purpose, veils should be doped with a conductive additive enabling them to maintain a high level of mechanical performance as well. Thermoplastic polymers doped with carbon nanotubes could be the best potential candidate materials for electroconductive veil fabrication. This is due to their low weight and the outstanding properties of carbon nanotubes. Moreover, there is no competitive material on the market yet. Commonly known are non-conductive veils produced from neat polymers or those obtained from carbon fibres covered by metal and stick together with chemical binder. From the technical point of view, the last two steps are undesired by product end-users. Hence, a much effort is focused on development of fabrication process of conductive veils from polymer and carbon nanotubes. The proposed technology is the melt blown manufacturing process. It allows fabrication of the final product (veil) through a highly cost-effective one-step route starting from polymer pellets/powder. There is no need to use solvents, processing compounds or binders for sticking fibres together. However, the incorporation of carbon nanotubes in the polymer network leads to a significant increase in the viscosity and decrease in the flow ability of the material. There are huge obstacles to its further processing. Therefore, it is necessary to make an appropriate selection of the polymer matrix and to control the properties of carbon nanotube-doped polymers at each stage of production. Especially, the polymer should have low viscosity (high MFI) and should be able to form fibres. As mentioned, conductive lightweight veils are not present on the market in an amount able to cover industry demand. Therefore, the next step is to increase the existing pilot plant for doped veil production for composite parts in the relevant environment (from TRL 4 to TRL 6). A semi-continuous pilot line for the industrial production of doped veils will be designed and the manufacturing layout will be developed. The main area in which electroconductive veils are highly desired is the aerospace industry or electronic sectors. Such materials could be applied in electromagnetic shielding or in lighting strike protection instead of presently used metallic meshes or tapes. Due to their low weight, the total mass of the aircraft could be reduced and its mechanical properties, i.e. fracture toughness, may be improved.