Recycling carbon fibre

The recycling of carbon fibre-reinforced plastics (CFRPs) not only makes sense from environmental and economic perspectives, it could also be key in increasing the penetration of these lightweight but expensive materials in high-volume markets such as automotive.

ELG Carbon Fibre (ELG-CF) has been doing pioneering work in this area, so when the company opened the doors of its factory in Coseley, UK, in June this year, Engineering Materials went along to find out more.

There are currently around 24,000 tonnes of waste carbon fibre generated each year by manufacturing operations, and ELG-CF managing director Frazer Barnes believes that with the expansion of the industry this will reach some 32,000 tonnes by 2021.

The recycling of carbon fibres, particularly those impregnated with resin, presents a significant challenge. The majority of CFRPs are made using thermoset matrices such as epoxy that cannot be melted or reshaped after they are cured.

But Barnes doesn’t see this as a problem, rather he believes this waste material represents a massive opportunity. His company has developed a process for reclaiming carbon fibre that is both efficient and affordable. As a result, he says that the cost of recycled carbon fibre is typically 40% less than that of virgin fibre, and similar weight savings can be achieved through its use.

Perhaps of equal importance, particularly for carmakers, is the fact that the use of recycled carbon fibre has a reduced impact on the environment. Barnes says that recycled fibre uses only around 10% of the energy required for the manufacture of virgin fibre. This saving is significant. According to life cycle analysis, a vehicle may need to be driven 155,000km before the fuel savings made possible through the use of CFRP eclipses the energy needed for its manufacture. Using recycled carbon fibre for the same application, this balance is achieved in less than 15,000km.

ELG-CF was founded in 2003 as Milled Carbon, and was essentially a research and development company with a pilot pyrolysis process for the recycling of CFRP. Once the concept was proved, Recycled Carbon Fibre was set up in 2008 to commercialise this technology. Recycled Carbon Fibre then became ELG-CF when, in 2011, established metals recycler ELG Haniel of Duisburg, Germany – looking for the next big thing – bought the company.

In those days, Barnes says, “it used to be a celebration if the plant produced one tonne of material in a week”. In 2015, by optimising the processes and infrastructure at its facility, ELG-CF produced 1080 tonnes of material in total.

ELG-CF has contracts in place with a number of companies that will supply it with the waste material it needs until 2022. Having this feedstock in place is essential if ELG-CF is to sell to automotive original equipment manufacturers (OEMs). The company receives both manufacturing waste and end-of-life parts, with the former accounting for the majority.

The first stage of ELG-CF’s recycling process involves the removal of any material that may be disruptive to the process, such as metal. Manufacturing waste from known sources can usually go straight to the furnace; trials may be necessary if the waste is less well understood.

End of life parts must be shredded first using a massive Vecoplan machine, which is capable of processing cured laminates of up to 55mm in thickness. Barnes says that it has taken 12–18 months of testing to determine the optimum parameters to shred these materials.

Key to the process, he says, is ensuring that the composites delaminate so that their surface area is increased, which helps with the subsequent pyrolysis. The resultant shredded laminates are feather-like in appearance.

In pyroloysis, CFRP scrap (in the form of dry fibres, cured and uncured prepreg, and laminates) is heated to 400–650°C in the absence of oxygen, burning-off the matrix material. Harmful gases emitted by thermoset resins during the process are siphoned off and incinerated, in accordance with environmental guidelines, separately from the fibres. The furnace is being improved continually to increase its efficiency, both to reduce costs and to ensure that ELG-CF meets its environmental responsibilities.

The process yields a tough and abrasive cotton-wool-like fuzz of carbon fibre, which maintains 90–95% of its original mechanical properties. After several years of product development, ELG-CF has managed to convert this material into several useful forms. Barnes says: “It’s taken a long time to industrialise these processes as fluffy carbon fibre is a very difficult material to handle.”

ELG Carbon Fibre’s principle products for use in automotive applications include: Carbiso CT, a short fibre product for the production of injection and compression moulding compounds; Carbiso M nonwoven mats that can form the basis of structural sheet moulding compounds (SMCs) and fast-curing prepregs; Carbiso TM, nonwoven mats manufactured from recycled carbon fibres blended with thermoplastic fibres, which can be compression moulded to form structural mouldings.

These products are not drop-in replacements for virgin carbon fibre. Indeed, the biggest challenge according to Barnes is creating a market for them. He says: “We’re trying to create a market for a new material, and we’re making it more difficult for ourselves because we are looking to those new applications of carbon fibre in areas like automotive.”

That work seems to be paying off. The materials are being used in Gordon Murray Design’s CFRP-intensive iStream Carbon chassis, which forms the basis of Yamaha’s MOTIV.e city car and the new TVR, which will be launched at Goodwood Revival this month. Bright Lite Structures is using ELG-CF’s nonwoven mats to manufacture the CFRP chassis of the Xenos E10 sportscar.

Perhaps most significantly, ELG-CF has been awarded its first production contract with a major OEM for a vehicle that will hit the road at the end of 2017. The company is also running end-of-life recycling trials with a number of OEMs.

ELG-CF is now looking to expand in the USA and Germany.

“We’ve proven out the carbon fibre business here on this site, and now we’re looking to expand that globally,” concludes Barnes.

Author
James Bakewell

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