Researchers develop recyclable carbon fiber composites greener with thermoforming

Recycling advancement reduces costs and greenhouse gas emissions of material’s second life by 90% to 95%

Researchers at US National Renewable Energy Laboratory (NREL) develops recyclable carbon fiber composites using bio-derivable epoxies, represent some of the most promising solutions yet for decarbonizing the vehicle manufacturing process and beyond. Nicholas Rorrer a senior polymer science researcher and group manager at the NREL, currently leads a team of researchers working to replace the heavy, resource-intensive steel parts in vehicles with recyclable carbon fiber composites. The ongoing project is supported by the U.S. Department of Energy’s Vehicle Technologies Office under the Composites Core Program in the Materials Technology subprogram.

The Key to Earth-Friendly Carbon Fiber Composites

When used in place of steel in vehicle components like hoods and roofs, carbon fiber composites can reduce the weight of a typical passenger car in half—boosting fuel efficiency by up to 35%—without sacrificing strength. This swap can free up weight and space for bigger batteries in electric vehicles, resulting in longer ranges and better energy efficiency.

But the benefits of traditional carbon fiber composites stop there. The material’s manufacturing processes are energy, greenhouse gas (GHG) emissions, and cost intensive, canceling out any environmental benefits.

“Traditional carbon fiber composites cost too much, are too brittle, and have high GHG emissions. Vehicle manufacturers aren’t interested in using them,” Rorrer said. “But transitioning to lighter vehicles using more affordable, strong, and Earth-friendly carbon fiber composites can be an important part of decarbonizing the transportation sector.”

In fact, carbon fiber composites made with NREL’s polymer science and engineering bio-derivable resin can be recycled at least three times. And a recent breakthrough by the NREL team may make their reuse even more cost and energy efficient.

A More Efficient Recycling Process

NREL’s recyclable carbon fiber composites are made up of bio-derivable epoxies, anhydride hardener, and carbon fibers. Rorrer and his team initially used a multistep process called methanolysis to prove the material’s recyclability. The application of this process represented the material’s first step toward circularity, a model of production and consumption that extends the life cycle of products—making the carbon fiber composites cheaper and greener when used across multiple lives.

In methanolysis, an inexpensive catalyst is added at room temperature to trigger chemical depolymerization, a process that causes the components to separate. Researchers can then reclaim the original carbon filaments for reuse with new bio-derivable epoxies and anhydride hardener.

“With thermoforming, you can skip all of that,” Rorrer explained, referring to the process of separating the material’s components in methanolysis. The impact of this work is detailed in the NREL presentation, Bio-Based, Inherently Recyclable Epoxy Resins to Enable Facile Carbon-Fiber-Reinforced Composites Recycling. “We have shown that you can simply press the material into different shapes to reuse them. And when you use both chemical depolymerization and thermoforming, you can reduce the cost and GHG emissions of the material’s second life by 90% to 95% compared to the first life of the material.”

The NREL team’s thermoforming process saves time and energy by allowing the material to stay intact. In thermoforming, researchers heat the recyclable carbon-fiber-reinforced composite to just above the boiling point of water and press it between two molds to shape the material for its next use.

But Rorrer and his team are not finished improving the material’s recycling process. The team is continuously exploring strategies for making thermoforming even easier, faster, and more energy efficient.

Rorrer is determined to continue developing NREL’s recyclable carbon fiber composites as a cost-effective, lightweight, and environmentally friendly alternative to steel. Beyond its use in vehicles, the team is studying the material’s performance in applications like wind turbine blades. Future partnerships also present the opportunity to unlock additional applications by considering other manufacturing processes.