CompositesWorld
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OCTOBER 2017 6 CompositesWorld COMPOSITES: PAST, PRESENT & FUTURE ยป Graphene, discovered at Manchester University (UK) in 2004, is a single, 2D layer of carbon atoms, tightly packed in a hexag- onal lattice structure. In simple terms, it is the thinnest, stron- gest material yet discovered and the most efficient conductor of both heat and electricity currently available. A single-wall carbon nanotube (SWCNT) is a tubular structure that can be thought of as a rolled sheet of graphene joined to form a seamless tube. Typically around 1 nm in diameter, a CNT can be millions of times longer. Given their near perfect blend of material properties and the fact that they are inherently lightweight and almost completely trans- parent, graphene and SWCNTs have been touted as breakthrough materials for more than a decade. Some observers are now asking the question, "When will they really deliver on the hype?" As a co-founder and managing director of Future Materials Group, I take the view that truly revolutionary materials take significant time to establish themselves commercially. To realize the long-term potential of graphene and SWCNTs most definitely will require patient, continued development in relevant sectors. Successfully placing a new material into an established industry sector is a huge challenge. One only has to look at once new material solutions that we now consider mainstream to see how long this process can take. Carbon fiber composites, as we know them in primary aerostructure applications, were available in the 1960s, but more than 30 years passed before we saw the first primarily carbon fiber composite airframe in Boeing's 787 Dream- liner. e benefits of carbon fiber were abundantly clear and desir- able, but considerable time was still required for testing, develop- ment of production processes and a credible supply chain to allow the introduction of this innovative new technology versus the incumbent or alternative material solutions. Graphene and CNT use today Graphene and CNT applications within the advanced composites sector are still at a relatively early stage of the commercializa- tion process, but as the availability of materials or dispersions of consistent quality has increased, a number of composite materials and components are starting to incorporate these nanomaterials. In terms of commercially available finished products, the sporting goods sector has been traditionally extremely agile when new materials become available. It has seen the greatest uptake so far for graphene and carbon nanotubes. Tennis racquets, bicycle frames, wheels, helmets, baseball bats, archery arrows, golf clubs and fishing rods have all been launched using the nano-mate- rials to provide users with lighter, stronger, faster, stiffer or more durable equipment. Of course, the performance benefit of nano- materials is sometimes difficult to independently verify, but that is not necessarily a barrier to sales in this market. Composite materials such as thermoset carbon fiber prepregs with resin systems modified with graphene or CNTs have been in the marketplace since around 2010. Manufacturers such as Zyvex and OCSiAl (both in Columbus OH, US), Gurit (Newport, Isle of Wight, UK), and Haydale Composite Solutions (Loughborough, UK) in collaboration with SHD Composites (Sleaford, UK), have targeted nano-enhanced materials to customers who require improvements in properties, such as fracture toughness, compressive strength and thermal conductivity in composite tooling. So far, the nano-manip- ulation has been focused on resin technology. Nano-manipulation of fibers within a reinforcement fabric, or CNT stitching of laminate plies, are in development but still many years from translating their results into higher performance composite part production. Demonstrating real-life benefits e use of composites that contain graphene and/or CNTs in aero- space might be seen as inevitable, given the strength, stiffness and compression-after-impact potential of the materials, but other func- tional properties are driving the more promising applications. Using graphene to enhance the electrical conductivity of the epoxy resin in a carbon fiber prepreg aileron demonstrator part, a recent National Aerospace Technology Exploitation Programme (NATEP, Farnborough, UK)-supported GraCELS project, demonstrated much improved heat dissipation throughout the part and massively reduced the heat damage seen in a lightning strike event. Performed with input from Airbus UK (Broughton, UK), Haydale Composite Solutions, BAE Systems (Farnborough, UK), SHD Composites, and Cobham Technical Services (Kidlington, UK), the project, impor- tantly, also identified improved mechanical properties and used existing manufacturing processes, making these materials suitable for other composite structures, such as wind turbine blades, that currently use coatings or metallic meshes to dissipate static charge. Ultimate design flexibility for parts with complex geometries and very low production volumes make additive manufacturing (AM) a go-to production route for thermoplastic composite parts that benefit from a customized design. Previously considered more suitable for models and test components, the newest AM mate- rials provide viable options for production tooling and commercial medical devices, automotive parts and aerospace components. Print filaments using graphene and CNTs are now available from Directa Plus SpA (Lomazzo, Italy), Haydale and Graphene 3D Lab (Calverton, NY, US), 3DXTech (Byron Center, MI, US) and powder and pellet format materials are available for other AM processes. Along with the increased mechanical performance, functionality such as magnetism, and heat and electrical conductivity can be added, with the long-term target to achieve performance on a par with metallic components. What is holding back progress? Possibly the biggest challenge is the development of large-scale, consistent raw material and compound supply chains at an affordable price. Graphene, for example, can be produced in sheet, platelet or powder form by growing it on a silicon carbide wafer, by chemical vapor deposi- tion (on Ni, Cu, etc.), by chemical reduction of graphite oxide, Graphene and CNTs: Commercialization after the hype