USC researchers have developed a new process to upcycle the composite materials appearing in automobile panels and light rail vehicles, addressing a current environmental challenge in the transportation and energy sectors. The study recently appeared in the Journal of American Chemical Society.

I wasn’t sure if it was possible to fully recycle composite materials. As wonderful as these materials are for making energy-efficient vehicles, the problem with composites is we don’t have a practical route to recycle them, so the materials end up in landfills.Travis Williams, professor of chemistry at USC

The chemistry demonstrated in the study, a partnership among Williams and professors Steven Nutt of the M.C. Gill Composites Center at the USC Viterbi School of Engineering, Clay C.C. Wang of the USC Alfred E. Mann School of Pharmacy and Pharmaceutical Sciences and Berl Oakley of the University of Kansas, is a new approach that shows that composite materials can be recovered and recycled in a manner that preserves the integrity of the materials.

Carbon fibers are thin fibers made of carbon atoms; they’re extremely lightweight but have very high tensile strength and stiffness ideal for manufacturing. A polymer matrix is a plastic-like, rigid material (such as epoxy, polyester or vinyl resins) that acts as a binder; a polymer holds carbon fibers together and gives composite materials their shape. A CFRP, or carbon fiber-reinforced polymer, is a composite material that combines the components of carbon fibers and polymers.

The study demonstrates the first successful method to reclaim high value from both the carbon fiber and polymer matrix of CFRP materials.

—Travis Williams

The challenge with CFRPs is that you can’t melt them or rebind them, which makes them difficult to separate and recycle at the end of their useful life, Williams said. The only recycling method available, applied to about 1% of composite waste, is to burn off the polymer matrix.

Nutt, professor of chemical engineering at USC Viterbi, takes exception to this strategy, saying, “The matrix is an engineered material that we do not want to sacrifice.”

Projections indicate that by 2030, 6,000-8,000 composite-containing commercial aircraft will reach end of life, and by 2050 retired wind turbines will generate 483,000 tons of composite waste. Williams said his lab’s upcycling method offers a sustainable solution to a growing waste problem.

The upcycling method saves the carbon fibers of the CFRP, which are the strong, durable part of the material. These fibers stay in good condition, and the team showed how they can be reused in new manufacturing, keeping over 97% of their original strength. This method is the first to successfully claim value from both the matrix and carbon fiber parts of CFRPs, turning waste into useful products and reducing environmental harm.

Biotechnology is crucial for recovering value from the discarded polymer matrix. The researchers also introduced a special type of a fungus called Aspergillus nidulans that was first engineered in the Berl Oakley lab at the University of Kansas. The USC team found that this fungus can rebuild the material from the composite matrix after the fiber recycling reaction chops the polymer into benzoic acid, which is then used as a food source for the fungus to produce a chemical called OTA ((2Z,4Z,6E)-octa-2,4,6-trienoic acid) using an engineered strain of this fungus.

OTA can be used to make products with potential medical applications, like antibiotics or anti-inflammatory drugs. This discovery is important because it shows a new, more efficient way to turn what was previously considered waste material into something valuable that could be used in medicine.

—Clay C.C. Wang

The upcycling method not only demonstrates the potential of using fungi for biocatalytic upgrading of waste materials but also highlights a novel approach to recycling composite materials by recovering both fibers and matrix components as high-value products.

Resources

• Composite Recycling with Biocatalytic Thermoset Reforming; Clarissa Olivar, Zehan Yu, Ben Miller, Maria Tangalos, Cory B. Jenkinson, Steven R. Nutt, Berl R. Oakley, Clay C. C. Wang, and Travis J. Williams Journal of the American Chemical Society doi: 10.1021/jacs.4c10838