Salvaging resin precursors from used tyres

US researchers have discovered a new way to put tyres that are no longer on the road back into the loop. Chemical recycling is central to this innovation.

Nearly 275 million end-of-life tyres are discarded across the United States every year with most ending up in landfill. An R&D team at the University of North Carolina in Chapel Hill is exploring how used rubber can be broken down into viable industrial materials, specifically precursors for epoxy resins used in adhesives, wind turbines and automotive parts.

Sustainable skeleton

The work, which has been published in the journal Nature, could be a game-changer for a ‘substantial’ amount of rubber which would otherwise accumulate in landfills, says lead author Aleksandr Zhukhovitskiy.

His team is focussing on what he calls ‘editing the skeletons’ of plastic materials, changing the structure of polymers to make them easier to process and reuse. In the case of tyre rubber, the researchers used a ‘gentle’ chemical process to insert nitrogen atoms into the material, breaking it into smaller, soluble pieces.

‘Rubber is made of carbon atoms tightly linked together, which makes it really tough to deconstruct,’ Zhukhovitskiy explains. ‘But if you change its chemical composition, you can open the door to breaking it down – and then build something entirely new from the pieces.’

Unlike traditional recycling methods, such as shredding tyres into crumbs or using high-heat pyrolysis, the university’s chemical process operates at lower temperatures and uses environmentally friendly solvents. Zhukhovitskiy says this yields a cleaner, less energy intensive, alternative that does not negatively impact the polymer’s mechanical properties as existing methods do.

Promising solution

The researchers introduced a sulphur diimide reagent that enables the installation of amine groups at specific locations in the polymer chains. The result is a liquid solution that contains amine-functionalised polymers, which can then be used to create epoxy resins with performance properties similar to those from Bisphenol A.

The team reports a molecular weight reduction from 58 100 g/mol to about 400 g/mol, with aminated post-consumer rubber being fully deconstructed over just six hours. This was possible under ‘mild’ conditions of 35-50°C.

While the innovation offers promising environmental benefits, it’s still in the early stages. Zhukhovitskiy says scaling the process to industrial levels will require further research, collaboration with engineers and significant financial backing.

The initial work was supported by the US Department of Energy.