Graphene and CNTs: Commercialization after the hype

Graphene and CNT applications within the advanced composites sector are still at a relatively early stage of the commercialization 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.

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Graphene, discovered at Manchester University (UK) in 2004, is a single, 2D layer of carbon atoms, tightly packed in a hexagonal lattice structure. In simple terms, it is the thinnest, strongest 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 transparent, 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 Dreamliner. The benefits of carbon fiber were abundantly clear and desirable, but considerable time was still required for testing, development 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 commercialization 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-materials to provide users with lighter, stronger, faster, stiffer or more durable equipment.  Of course, the performance benefit of nanomaterials 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 Technologies Inc. and OCSiAl (both in Columbus OH, US), Gurit UK (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-manipulation 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

The use of composites that contain graphene and/or CNTs in aerospace might be seen as inevitable, given the strength, stiffness and compression-after-impact potential of the materials, but other functional 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, importantly, 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 materials 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 deposition (on Ni, Cu, etc.), by chemical reduction of graphite oxide, by unzipping an SWCNT or by exfoliation (peeling away single graphene layers) in solid or liquid phase. These diverse routes offer various combinations of yield, purity and cost and a relatively small number of industrial-scale suppliers.

When the raw material supply matures, these new materials still face significant challenges that are not always apparent when research reveals potential outstanding properties. New materials can carry risk and whilst graphene and CNTs promise much, an industry such as commercial aerospace will need to be sure conductive CFRP doesn’t impact other properties, such as long-term fatigue performance. Whilst these materials do have some amazing properties, there are also issues. Research lauds graphene’s exceptional conductivity, but no way yet exists to easily switch off and swtich on the flow of current, the way it is done with semiconductors such as silicon in microprocessors. This is holding back a breakthrough speed advance in electronics applications. 

Existing, well-established technologies and supply chains also pose a challenge to graphene and carbon nanotubes as their manufacturers and end-users drive to demonstrate to OEMs collectively that their performance benefits justify both material costs and the cost of change.

 

Outlook for the future

Whilst other industry sectors, specifically, energy storage and electronics, are sometimes touted as the biggest prizes for graphene and CNTs, the advanced composites sector appears to have commercialized them more rapidly. This trend is expected to continue during the next decade as the global supply base matures and the continued early-stage development of current research projects identifies truly beneficial composite applications.

It is difficult to forecast exactly how rapidly the overall market for graphene and CNTs will grow, primarily because of the challenges discussed above. Taking graphene as an example, current materials markets are in the low- to mid-tens of millions of dollars, with researchers and investment analysts suggesting a figure in the range of US$200 million-US$500 million by 2025.      

Investment in research and in production development will need to be at an even higher level for some years, yet in any case, full commercialization isn’t likely to come until next decade. The most successful market entrants will be those best able to match specific performance gains to a targeted market sector whilst also best navigating a smooth path through existing value chain resistance.

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