Fungi could provide the key to recovering valuable chemicals from discarded carbon fiber — a material used extensively to make sports equipment, aircraft, or the blades of wind turbines, among many other uses.

The demand for carbon fiber has been steadily growing, with hundreds of thousands of tons being produced around the world every year. However, this material is notoriously difficult to recycle.

“Carbon fiber is usually woven like a fiber and combined with a polymer matrix that holds everything together,” said Berl Oakley, professor of molecular biology at the University of Kansas. “The result is a very light and extremely strong material.”

The same structure that makes carbon fiber such a strong material, also makes repairs impractical and recycling difficult. As a result, carbon fiber ends up in landfills or incinerated.

By 2030, thousands of commercial aircraft built with carbon fiber will have to be discarded, and by 2055, millions of tons of waste from wind turbines will follow suit.

“Going forward, it becomes increasingly important to be able to recycle carbon fiber,” stressed Oakley. The new upcycling method developed by his team could take us one step closer to making this possible, as it is the first to have shown carbon fiber waste can be turned into a valuable chemical with a wide range of applications in chemistry and medicine.

Recycling carbon fiber

The new carbon fiber recycling process takes place in two stages. The first involves a chemical method involving high pressure and temperature, where the polymer matrix is dissolved and stripped away from the woven carbon fibers. This allowed the scientists to recover the free carbon fibers, which retained 97% of the tensile strength of the original material. These recovered fibers can then be used to manufacture second generation carbon fiber composites.

“It’s impressive,” said Oakley. “The recovered fibers are almost indistinguishable from the virgin fibers.”

But what makes the new method unique is that it is the first to recover a valuable chemical from the matrix component of carbon fiber — and here is where fungi play an essential role.

The first stage of the recycling process converts the carbon fiber matrix made of polystyrene into a chemical called benzoic acid, which the fungus Aspergillus nidulans can feed on. The researchers took advantage of this natural process in the second stage of the process to produce a valuable compound known as octatrienoic acid.

“There is an interest in octatrienoic acid as a building block chemical for making many other things,” said Oakley. “Aspergillus nidulans makes it natively but not much of it, so we had to turn up the production using genetic engineering.”

The engineered fungi were able to make octatrienoic acid from benzoic acid with an efficiency 20 times higher than any previous attempts by other research groups, which had tested similar processes using bacteria. In addition to being more efficient, fungi can be grown more cheaply than bacteria, which can be a key advantage to make the process viable at an industrial scale. 

The whole recycling process takes place within one week, offering a fast option to fully recycle carbon fiber materials.

Scaling up

This is the first method to enable the recycling of both the woven fabric and matrix components of carbon fiber. The process is designed to eventually be run at an industrial scale, starting with the final product, octatrienoic acid, which can be used to make a variety of different molecules, including products with medical applications such as antibiotics or anti-inflammatory drugs.

“For this process to be useful, you want to make something that is going to be used in bulk,” said Oakley.

While the researchers have offered a proof-of-concept for the recycling of carbon fiber, the new method will have to be scaled up to establish itself as a viable solution. It also remains to be seen how the recycling process would compare to the manufacturing of virgin carbon fibers at an industrial scale, particularly in terms of cost and environmental impact, which will be necessary to make the solution competitive in the market.

The scientists are currently in the process of patenting the recycling method, which will help them secure funding to start scaling up the process. According to Oakley, scaling up this process is perfectly feasible, since Aspergillus fungi are already used in industrial-scale fermentation processes to make all kinds of molecules, including enzymes found in detergents and many food additives, such as citric acid.

The next step for the researchers will be to improve the yield of octatrienoic acid that the fungi are able to make. Since the project started, Oakley’s research group has developed new strains of A. nidulans that are more efficient — their plan is to engineer these newer strains to do the same process with the goal of achieving a much higher yield of octatrienoic acid.

“There’s plenty more work to be done,” said Oakley. “We think we can boost the yield by a lot.”

Reference: Clarissa Olivar et al., Composite Recycling with Biocatalytic Thermoset Reforming, Journal of the American Chemical Society (2024). DOI: 10.1021/jacs.4c10838