A composite made in heaven

Materials World magazine
,
1 Apr 2018

Composite materials have been around for centuries, and yet materials scientists remain focused on how different combinations might bring compounded benefits in modern day applications. Dr Jennifer Unsworth and David Stanier of intellectual property firm, Withers & Rogers, report.

Carbon fibre has been widely used in the aerospace sector to date, where its high stiffness-to-weight ratio can help drive fuel efficiency. More recently, it has found use in the manufacture of high performance sports equipment – everything from bikes to tennis racquets. Now, a focus on creating new, improved materials that combine the properties of carbon fibre and graphene are generating new opportunities in engineering design.

 Developing composite materials involves matching the specific and auxiliary properties of each component. While the tensile properties of carbon fibre are excellent, the fibres don’t perform well in compression or shear, and instead rely on resin to glue them together. However, resins can create regions of weakness within composite structures so it is important to find mechanisms to transfer stress away from the resin into the fibres or to directly reinforce the resin.

Known for its incredible strength and minute particle size, when graphene is added to the carbon fibre resin, it can offer significant improvements. Alternatively, it can be attached to the carbon fibres using a chemical bonding process, which helps to anchor them in the resin and improve the material’s overall strength.

Take it to the sky

As might be expected, many of the early applications of this innovative material have been in the aerospace industry. Boeing recently secured patent protection (US9518160) for a means of adding graphene directly to carbon fibre resin to improve its strength and stiffness, at the same time as enhancing its electrical and thermal conductivity.

Taking a different approach, the Korea Institute of Machinery and Materials recently received patent protection (KR101436500B1) for a process of reinforcing carbon fibres through the application of a graphene coating. This acts as a strengthening interface, allowing stress to be transferred away from the resin into the reinforced fibres, which are inherently stronger.

When considering potential applications for composite materials, sometimes one or more of the auxiliary properties of a component material are the main reason for their selection. As well as being very strong and lightweight, carbon fibre/graphene composites offer enhanced electrical and thermal conductivity for example, which means they are ideally suited to applications involved in protecting aircraft from lightning strikes.

Global aerospace OEMs, Goodrich Corporation and Rohr Inc, have recently patented a means of using carbon fibres reinforced with graphene to make nacelles and nacelle components in aircraft engines. As well as being strong and lightweight, the material has been chosen for its enhanced electrical conductivity.

Patent-filing data also reveals a high level of interest in carbon fibre/graphene composite technology among sports equipment manufacturers and an initial search in this category has revealed there are currently 10 patents pending at the European Patent Office. Whilst carbon fibre has long been used to make ultra-lightweight sports equipment, the addition of graphene can deliver further marginal gains in terms of weight reduction. While not always significant enough to justify the extra cost of production, these benefits can make a big difference to a sports team’s overall performance.

With marginal gains in mind, Vittoria, a leading producer of bicycle tyres and wheels, is using graphene to reinforce carbon fibre road rims that are stronger and lighter than those made using carbon fibre alone. A bike helmet made from a carbon fibre/graphene composite, which is better at absorbing impact than a traditional, polycarbonate roll cage, has also been developed recently by sports equipment manufacturer, Catlike Sport Components and is the focus of this magazine edition’s Patent of the Month article. Other areas of application in the field of sports equipment include coatings for skis, a high-performance tennis racquet and even a fishing rod.

Surprising function

In future, we should expect to see wider application of multi-functional composites – materials that combine the mechanical benefits of two or more materials with less obvious benefits such as improved permeability, magnetic properties or electrical conductivity. Taking this approach to reality, the possibilities are endless. 

A recent innovation by a group of academics at the University of Hawaii, USA, has developed a composite layer with carbon nanotubes grown from the fibres. This enhances its overall properties, but particularly improves its through-thickness properties to prevent delamination occurring between layers. Importantly, the material is also better at conducting electricity, which allows structural health monitoring techniques to be used to assess structures for damage, even while in use.

For the innovator, a key consideration when developing composite materials for specific applications can be the issue of patentability. As each component material is likely to have been widely used prior to its use in a multi-functional composite, this could, in theory, make the innovation more difficult to protect. However, as long as the new multi-functional composite technology can be shown to deliver surprising advantages or improve the properties or functionality beyond expectations, it should be possible to secure patent protection for the innovation, guaranteeing its owner a 20-year period of commercial exclusivity.