Some of the toughest plastics in use—the epoxies in airplane wings, car parts, and protective coatings—are thermosets, materials whose molecular chains are permanently locked together during manufacturing. That strength comes at a cost: once set, they can’t be melted and reshaped. Most end up in landfills or incinerators.
Researchers at the New Mexico Institute of Mining and Technology have now extended the recyclability of a thermoset from 2 or 3 cycles, typical for today’s thermosets, to 12 (Cleaner Mater. DOI: 10.1016/j.clema.2026.100395).
Recyclable thermosets can be made using the Diels-Alder reaction, in which two molecules form a strong bond at low temperatures and separate at high temperatures. By using these reversible bonds as the cross-links in a thermoset, chemical engineers can create a material that is rigid under normal conditions but that can be softened and reshaped by heating.
Each heating cycle releases small reactive molecules called maleimides, which are supposed to reconnect to the molecular network as it cools. Instead, some of those maleimides bond to each other, forming links that cannot be reversed. After just two or three cycles, so many of these dead-end bonds have built up that the material becomes permanently rigid again.
The researchers found that adding ethyl and methyl groups to the maleimide molecule slows the unwanted side reaction, giving them more time to reshape the material at high temperatures before irreversible bonds form. “We were able to reprocess our modified epoxy 12 times without significant loss in strength or stiffness,” author Samantha Knight says.
“The work is a good demonstration,” says Bharath Venkatesh, a chemical engineer at ExxonMobil who was not involved in the research. “It all depends on increasing the processability windows or increasing the number of possible life cycles,” he says. “The economics have to make sense at scale.”
2026 American Chemical Society
