The Case for Recycled Carbon Fibre in Auto Lightweighting

By Frazer Barnes, Managing Director, ELG Carbon Fibre Ltd.

carbon fiber imageBackground

After decades of steady but moderate growth, the selection of carbon fibre composites for the primary structure on the Boeing 787 marked a turning point in development of the industry. From that point onwards, carbon fibre has been considered as an option whenever high performance and low weight has been a requirement. More recently, the use of carbon fibre by BMW in its i3 model marked another turning point, this time in the automotive market, with carbon fibre being used in high volumes on a production vehicle. The growth in the use of carbon fibre that these developments have spurred creates new challenges—among them how to reduce costs, to ensure that carbon fibre composites can compete with other high performance materials, how to deal with both the manufacturing and end-of-life waste that will be generated from the increased use of carbon fibre, and how to avoid the supply and demand imbalance that has been a characteristic of the carbon fibre industry.

Carbon Fibre Recycling

Fortunately, the solutions to these challenges are not exclusive. Recognising the growth that the carbon fibre industry was about to experience, several companies, with ELG Carbon Fibre among them, have been investigating how to recycle carbon fibre for several years. In the case of ELG, this has resulted in a commercial scale carbon fibre recycling operation that can process over 2,000 tonnes of carbon fibre containing waste each year, and produce over 1,000 tonnes of recycled carbon fibre products that can be returned to industry (output in 2015 was just over 1,000 tonnes). Although most of this material is used in other industries today, we see one of the main markets in the future being lightweighting in the automotive industry. The reasons for this are discussed below, but first it worthwhile describing the recycled carbon fibre materials that are available today.

Recycled Carbon Fibre Materials

Photo 2In general, recycled carbon fibre materials are available that can be used in either the compounding industry or the composites industry.

The products for the compounding industry are short fibre materials, with lengths ranging from 80µm to 12mm. These materials are available as free flowing powders (for the very short fibre materials), chopped fibres or as pellets which are easier to handle in downstream production processes. The principal benefit of using recycled carbon fibres for these applications is that they provide exactly the same properties as virgin carbon fibre, at approximately 60% of the cost. Thus, they open up the possibility of replacing glass fibre in reinforced thermoplastics, providing the same level of structural performance at reduced weight, or at increased loading providing improved mechanical performance such that they become viable alternatives to either aluminium or magnesium.

Table 1

The products for the composites industry are long, discontinuous fibre products, where the fibre length is typically between 50mm and 150mm. The most common form in which these materials are supplied are as nonwoven mats. These can be made from carbon fibre alone, in which case the mats can be used with liquid moulding processes, or as the reinforcement for prepregs and sheet moulding compounds. They can also be made from blends of carbon fibre and thermoplastic fibres such as PP, PA and PPS, in which case laminates can be made directly by compression moulding.

Extensive testing shows that the properties of materials based on recycled carbon fibres are similar to those of the same type of materials based on virgin carbon fibres; the main difference is cost, which is typically 30%-40% lower for the virgin carbon fibre products. This is very relevant to the automotive industry, where although there is a strong imperative for lightweighting, it has to be at economic cost.

Photo 3

Supply Chain Security

One facet of the automotive industry is that even though the mass of individual components may be low, production volumes are orders of magnitude greater than those typically found in the composites industry. This means automated manufacturing processes, which in turn demand consistent raw materials. While this can be problematic with other plastic materials, the fact is that there are just a few grades of carbon fibre that are used in very high volumes, and the production programmes that use these fibres will be running for at least another 25 years. The total amount of carbon fibre waste that was produced during manufacturing in 2015 was around 24,000 tonnes, thus stable supplies of feedstock exist, from which very consistent products can be made to support high volume automotive programmes. Moreover, as the components that use these materials reach the end of their lives, an additional high volume sources of feedstock open up.

Indeed, it may be that recycled carbon fibres offer a more stable supply chain than virgin carbon fibres. After a period of oversupply in the carbon fibre market, as a result of the global economic downturn and investments in additional carbon fibre manufacturing capacity, forecasters are again expecting demand to outstrip supply in the next few years. The situation may not be as severe as we have experienced previously—new entrants to the carbon fibre market don’t have the same legacy business volumes they have to support—but nonetheless, it is unlikely that all of the forecast new business can be supported. Utilising the high volumes of waste carbon fibre provides more certain in the supply chain, to the benefit of both the end users and the wider composites industry.

Applications

Of course, not everything application is suitable for recycled carbon fibre alone. In some cases, the right option may be to use a high performance metal, or a glass reinforced plastic, in other cases the best option may be to combine virgin and recycled carbon fibres in the same component. The main responsibility of the industry is to make engineers aware of the possibilities of recycled carbon fibres, and to provide them with the data they need to properly assess the materials.

A good example of the use of recycled carbon fibres with other materials is the iStream Carbon concept, by Gordon Murray Design. This approach takes advantage of the benefits of both recycled carbon fibre and steel to provide a structure that is lightweight, durable and cost effective.

iStream® Carbon (photo courtesy of Gordon Murray Design)

iStream® Carbon (photo courtesy of Gordon Murray Design)

The final advantage provided by using recycled materials comes in the vehicle life cycle assessment, where the significantly lower embodied energy in the recycled carbon fibre products provides a large benefit. With car manufacturers increasingly using life cycle assessment as part of their materials selection process, this increases the potential applications of recycled carbon fibre.

Summary

In summary, there are strong economic, supply chain security and environmental reasons to consider recycled carbon fibre materials in the search for cost effective solutions for lightweighting in the automotive industry. With these materials now being produced in commercial volumes, and with the design data necessary to allow engineers to explore the possibilities of these materials now available, we can now expect these materials to increasingly feature in lightweighting solutions across the whole transportation sector.

FB Office PhotoFrazer Barnes is Managing Director of ELG Carbon Fibre, a pioneer and leader in the carbon-fibre recycling industry. He has more than 30 yeras experience in the composites industry, working with SP Systems (now Gurit), Cytec Engineered Materials (now Solvay) and Hengshen Carbon Fibre in the U.K., U.S. and China.

 

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