Researchers in Rice University’s Tour Lab have used flash Joule Heating (earlier post) to transform waste glass fiber-reinforced plastic (GFRP) into silicon carbide. A paper on the work is publishedin the journal Nature Sustainability.

Glass fiber-reinforced plastic (GFRP) is widely used in everything from aircraft parts to windmill blades. Yet the very qualities that make it robust enough to be used in so many different applications make it difficult to dispose of; consequently, most GFRP waste is buried in a landfill once it reaches its end of life.

With increased pressure from regulatory agencies to revise and improve recycling practices for end-of-life vehicles, there is a strong need for better methods to manage GFRP waste. While some have tried to develop approaches using incineration or solvolysis to get rid of GFRP, Yi Cheng, a postdoctoral research associate and Rice Academy Junior Fellow who works in the Tour lab, said such processes are less than ideal because they are resource-intensive and result in environmental contamination.

Tour’s lab has already developed new waste disposal and recycling applications using flash Joule heating, a technique that passes a current through a moderately resistive material to quickly heat it to exceptionally high temperatures and transform it into other substances. Tour said when he learned of the issues involved with GFRP disposal from colleagues at the Defense Advanced Research Projects Agency, he thought that this kind of turbo-heating could transform GFRP into silicon carbide, widely used in semiconductors and sandpaper.

We already knew that if we heat the mixture of metal chloride and carbon by flash Joule heating, we could get metal carbide—and in one demonstration, we made silicon carbide. So we were able to leverage that work to come up with a process to transform GFRP into silicon carbide.

—James Tour

This new process grinds up GFRP into a mixture of plastic and carbon and involves adding more carbon, when necessary, to make the mixture conductive. The researchers then apply high voltage to it using two electrodes, bringing its temperature up to 1,600-2,900 degrees Celsius (2,912-5,252 Fahrenheit).

That high temperature facilitates the transformation of the plastic and carbon to silicon carbide. We can make two different kinds of silicon carbide, which can be used for different applications. In fact, one of these types of silicon carbide shows superior capacity and rate performance as battery anode material.

—James Tour

While this initial study was a proof-of-concept test on a bench scale in the laboratory, Tour and colleagues are already working with outside companies to scale up the process for wider use. The operating costs to upcycle GFRP are less than $0.05 per kilogram, much cheaper than incineration or solvolysis—and more environmentally friendly.

The research was supported by the Air Force Office of Scientific Research (FA9550-22-1-0526), the US Army Corps of Engineers (W912HZ-21-20050) and Rice University.

Resources

• Cheng, Y., Chen, J., Deng, B. et al. (2024) “Flash upcycling of waste glass fibre-reinforced plastics to silicon carbide.” Nat Sustain doi: 10.1038/s41893-024-01287-w