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Innovations in carbon composite recycling — solving the pyrolysis problem

Tom Baker

By Tom Baker

Partner

The use of carbon fibre composites for consumer sporting applications has exploded. Traditionally used for niche applications like tennis racquets and golf club shafts, carbon fibre is now the material of choice for bike frames and many other components including handlebars and cranks. While the popularity of this wonder material is driven by a host of benefits, the elephant in the room is that it can be difficult to recycle or reuse products made from carbon fibre at end-of-life.

Thankfully, innovation is well underway to solve this problem.

The problem with pyrolysis

As the shift towards a circular economy continues, time and resources are being put into developing new recycling technologies. Carbon fibre composites require tonnes of energy to turn raw materials into the fibres themselves, so any fibres that still have functional value at end-of-life could certainly be reused if they can be removed from the carrier resin.

The most common way to do this currently is pyrolysis, which involves supplying heat in a low oxygen environment to separate the fibres from the resin carrier. However, this process typically produces fibres that are shorter and more jumbled up than new ones, reducing their downstream uses. Such fibres typically end up being used in non-critical applications, ranging from low-end tennis racquets to park benches.

Therefore, to improve the circular life of carbon fibre composites, the process needs to be refined to produce recycled fibres that are closer to (if not the same as) virgin fibres.

Potential solutions

ELG Carbon Fibre is one such innovator that has patented a pyrolysis plant (US10899042B) and process that produces recycled carbon fibres free of pyrolysis or carbonisation residues, which means that the properties of the fibres aren’t impaired. This involves the use of an indirectly heated rotary tube furnace with openings for the recovery of the carbon fibres, enabling the careful regulation of both temperature and proportion of oxygen. ELG argues that this results in recycled carbon fibres with properties that are more closely aligned with virgin fibres.

Vartega Inc takes an alternative approach, patenting a technique of treating composites with solvents in multiple stages under carefully controlled conditions of temperature and pressure (US10487191B). It’s argued that this enables the recovery of reinforcing fibres from the matrix material without damaging the fibres themselves.

Shocker Composites LLC takes another approach, with pending patent rights for the downstream processing of fibres that may have been produced from either pyrolysis or solvents that may not be suitable in their existing form for high strength composite applications. Its pending US application (US2021031409) is directed to densification of recycled fibres by a process of cutting, wetting and mixing the fibres to produce fibres of comparable quality to virgin fibres.

The future of carbon fibre

Ultimately, any technique that aims to recycle composite materials to produce high quality component materials suitable for reuse is going to be difficult and more energy intensive than recycling a homogeneous material.

These three approaches show that, whichever approach is followed, a significant amount of energy or additional materials (such as solvents) will be required. Currently, all three techniques have their merits and provide a useful output, with these processes sure to be refined over time where one may show to be better than the others.

If you’re innovating with advanced materials and need IP support, get in touch with me at teb@udl.co.uk.

Find out more about our chemistry and materials team.

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