Carbon fibre recycling method showing potential

Carbon fibres are thin strands of carbon that are exceptionally strong and lightweight. The fibres are combined with plastic to create a composite that can be used to construct a variety of products such as aircraft, wind turbines and sporting equipment, for example bicycles, hockey sticks or tennis racquets. Carbon fibre is the primary material used in Formula 1 race cars, which need to be as light as possible to increase performance.

UNSW Canberra researcher Di He has now developed a method to recycle carbon fibre in a way that not only wastes less of the material, but also uses less energy and leaves more of it intact and able to be turned into more useful new products.

According to He, the project was a collaboration with a partner in the automotive industry who wants to investigate building cars out of recycled carbon fibre.

Until now, recycling carbon fibre had always resulted in the material being heavily degraded. The mechanical performance of objects made from existing recycled fibres is degraded by 80–90% compared to new fibres. They are typically only reused to make low-value products like tables and chairs that do not experience heavy forces or loads.

“The existing method of recycling involves shredding the composite, which destroys the carbon fibre, before heating it to remove the plastic. After it has been shredded, the fibres look like individual hairs or cotton wool strands,” said He.

The new method doesn’t shred the carbon fibre, He said they have optimised how it is heated in a furnace.

“This leaves the fibres intact, and therefore the new product made from the recycled carbon fibre is much stronger.

“Our method degrades the carbon fibre by less than 30%, which is a 50% improvement on existing methods,” He said.

The recycled carbon fibre produced using He’s method is not suitable for constructing a car yet, but it is significantly closer to that goal than before. The recycled carbon fibre could potentially be used to construct individual parts of a car, such as a roof.

Car manufacturers are interested in carbon fibre vehicles as the lower weight can make the cars more energy efficient, helping them meet the new fuel efficiency standard announced by the Australian Government earlier this year. As the country transitions to electric vehicles, this would also help reduce vehicle electricity consumption, thereby increasing vehicle range.

Carbon fibre is expensive to make, which explains the appeal of recycled carbon fibre, in addition to its environmental benefits. Recycling carbon fibre requires one-tenth of the energy needed to produce it from scratch.

Matthew Doolan, a lead researcher from the UNSW Canberra Advanced Manufacturing Research Group, said that as the world progresses with engineering and technological advancements, it needed to think more about reducing waste.

“As we make more advanced products we also make them from significantly more advanced materials, and as a result we are creating problems at the end of the life of that product.

“The standard practice of just dumping these products, or burning them, is unsustainable and cannot continue forever.

“Exploring other options available to us is one of the key questions we’re hoping to help answer at UNSW Canberra,” Doolan said.

Carbon fibre recycled using the old method (left) compared with Dr He's new method (right). The recycled carbon fibre on the right is stronger and has the potential to be turned into more advanced products. Photo: UNSW Canberra.