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To avoid their disposal in landfills or recycling in high-energy, low-value industrial processes, scientists globally are developing ways to manufacture  carbon fiber-reinforced polymer (CFRP) materials that allow for triggered deconstruction and the recovery of high-quality carbon at the end of their life span. But this promising alternative still creates a waste stream of material with little value, notes researchers at the , who are exploring an innovative method using a renewable energy source to upcycle this leftover material.

Chemistry professor Jeffrey S. Moore, and postdoctoral researchers Yuting Zhou and Zhenchuang Xu, report in their recently  a method that uses electricity to modify this recycling byproduct in a way that converts it to useful material. “This closes a critical loop in the life cycle of carbon fiber composites,” Moore says. The research team’s modification of this byproduct happens at the molecular level through electrolysis, a process using electric current to drive a chemical reaction in a solution.

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The recycling byproducts are basically fragments of the original material — CFRP — consisting of molecules known as oligomers, smaller chains of repeating monomer units. CFRP consists of cross-linked polymer matrices and carbon fiber, or networks of polymer chains that reinforce the carbon fibers. By comparison, thermoplastics consist of linear polymers, long chains with many repeating monomer units. 

In deconstructing CFRP to recover the fibers, the polymer matrix is broken and leaves behind the waste fragments consisting of oligomers with low mechanical properties, Zhou explains. But through electrolysis, the researchers directly modify the oligomer backbone — the main structure of the polymer chain — at two different locations. In a single step, they modify the chain by installing two key functional groups at two carbon-hydrogen bond sites, which enables the modified oligomers to assemble into a new network formation.

“Those installed functional groups can link together, so we can link the fragments into a network,” says Zhou. “The goal is to link them [oligomers] back into a network and then restore the mechanical performance.”

In this novel dynamic network form, known as covalently adaptable networks (CANS), this polymer material again has strong mechanical properties and the ability to be reprocessed. “The practical significance is that we can now take low-value byproducts from composites recycling and convert them into new thermoset materials with high circularity,” Moore says. “This work contributes to net-zero waste manufacturing and highlights the potential of electrochemistry for polymer upcycling.”

The research team also reports significant chemical advances in their study, which they say is the first scalable demonstration of dual carbon-hydrogen functionalization along a complex polymer backbone. Previous approaches to this type of modification have been limited to mild changes, or relied on end-group chemistry, rather than directly “editing” the oligomer chain itself at the carbon-hydrogen sites.

“In doing so, we found that tertiary allylic carbon-hydrogen sites in these branched oligomers are more reactive than expected, which is important new chemistry in its own right,” Moore explains.

The team is already pursuing further studies, including possibly extending this electrochemical method to other materials, specifically polybutadiene, a key component in synthetic rubber and high-impact polymer blends.

This work was supported as part of the REMAT EFRC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences at the University of Illinois Urbana–Champaign.

The paper was published in Nature Synthesis and can be .