New Rubber Recycling Method Could Reduce Tire Waste

Rubber tires are built to last, but that durability makes them a nightmare to recycle. Now researchers at the University of North Carolina at Chapel Hill (UNC-Chapel Hill) have developed a mild, two-step chemical process that can break down synthetic rubber under environmentally friendly conditions. Published in Nature, the study shows how the method transforms used rubber into nitrogen-rich building blocks for new materials.

The rubber recycling problem

Each year, hundreds of millions of tires reach the end of the road – and not just on our vehicles. In the United States, more than 274 million tires were discarded in 2021. While some are repurposed for fuel or ground into materials like rubber mulch, nearly one in five still ends up in landfills, where they create long-lasting environmental problems. But tires don’t just take up space, they can leach harmful chemicals into soil and groundwater and are prone to spontaneous fires, which are difficult to extinguish and release toxic smoke into the atmosphere.

What makes tires so hard to recycle is the very thing that makes them so durable. Most are made from synthetic rubber, which consists of long chains of molecules called polymers. These chains are cross-linked – chemically bound together into a strong, flexible network through a process known as vulcanization. This structure gives rubber its strength and resilience, but also makes it highly resistant to breakdown, even under extreme conditions.

 

 

Traditional recycling techniques struggle with these challenges. Pyrolysis, one of the most widely used methods, involves heating rubber at high temperatures in the absence of oxygen to break it down into oils and gases. While it can recover some energy and materials, it often produces hazardous compounds such as benzene, toluene and dioxins, posing environmental and health risks. It also demands substantial energy input.

Another approach, de-vulcanization, targets the sulfur cross-links within the polymer network. This can make the material pliable again, but the process often compromises the mechanical integrity of the rubber, limiting its ability to be reused in demanding applications like tires.

 

 

Oxidative and catalytic cleavage methods attempt to chop up the polymer backbone itself but usually result in messy mixtures that are difficult to turn into anything valuable.

These challenges have sparked growing interest in finding a greener, more efficient way to recycle rubber – one that uses mild conditions, produces less waste and avoids toxic chemicals

A mild, two-step method to recycle rubber

Against the backdrop of growing waste and unsustainable recycling practices, a team led by Dr. Aleksandr Zhukhovitskiy, an assistant professor and William R. Kenan, Jr. Fellow at UNC-Chapel Hill, has developed a new approach for breaking down tough synthetic rubbers.

The method begins with a process known as C–H amination. Using a sulfur diimide reagent, the researchers introduced amine groups – chemical units containing nitrogen – at specific locations along the rubber’s polymer chains. These nitrogen-containing groups serve as chemical “handles,” setting the stage for a second transformation: a backbone rearrangement known as the aza-Cope reaction. This rearrangement weakens and breaks down the rubber’s molecular structure, converting it into soluble, nitrogen-rich materials.

 

 

What sets this process apart is not just its effectiveness but its environmental profile.

“We demonstrated that the entire process can be carried out in green solvents and at mild temperatures (35–50 °C),” Zhukhovitskiy told Technology Networks.

The new technique also avoids harsh oxidants or precious metal catalysts, both of which are common in traditional rubber recycling chemistry.

In a model system called oligocyclooctadiene, the team reduced the molecular weight of the rubber from 58,100 grams per mole to ~400, effectively breaking it down into its component parts. When applied to real-world used rubber, the process achieved complete degradation in six hours. The reaction proceeded even faster in the model systems, achieving full breakdown within two hours.

The process produced a soluble material rich in amine groups using standard commercial reagents. These materials can be further transformed into epoxy resins, a class of high-performance polymers widely used in coatings, adhesives and composite materials.

“The key takeaways are 1) that complex waste rubber materials could be transformed into building blocks for epoxy resins using a simple chemical process,” said Zhukhovitskiy, “and 2) installation of nitrogen atoms into the rubber is key to both enable the deconstruction of rubber and to expand the scope of applications of the deconstruction products.”

“In moments like this I come to appreciate the power of organic synthesis. It is fascinating to see the ease with which the developed sequence of simple, yet powerful, organic transformations can take on a stubborn C–C bond and convert polybutadiene and polyisoprene-based rubbers into potentially valuable epoxy resin,” said co-author Dr. Maxim Ratushnyy, former postdoctoral scholar at UNC-Chapel Hill.

To evaluate the sustainability of the process, the team also used a metric known as the Environmental Impact Factor, or E-factor, which measures how much waste is produced relative to useful output. While the overall E-factor (which includes solvent use) was high, the simple E-factor (excluding solvents) was much lower.

“A direct, apples-to-apples comparison of our method to traditional ones is not feasible for a number of reasons, but qualitatively, our process is expected to require far less energy than pyrolysis,” said Zhukhovitskiy.

Toward a greener future for rubber waste

By breaking down tough, synthetic rubbers under mild, environmentally friendly conditions, the process could lead to a system that is both chemically efficient and aligned with sustainability goals.

A key outcome of this work is that it enables rubber waste to be transformed into chemically valuable materials, rather than being incinerated or sent to landfill. Most epoxy resins are derived from petroleum-based chemicals. A method that allows rubber waste to be repurposed into feedstock for these materials could help reduce dependence on fossil resources, while also giving new value to a material that is otherwise difficult to recycle.

The approach aligns with several of the 12 principles of green chemistry, including mild reaction conditions, reduced energy input and the avoidance of harsh or toxic reagents. While the process still has room for improvement, it represents a step forward in designing more environmentally conscious chemical recycling techniques.

As with many early-stage technologies, there are challenges ahead. One area the researchers identified is solvent use. While the reactions can be carried out in aqueous or greener solvent systems, the total solvent volume contributes to the process’s environmental footprint.

“To improve the sustainability of this process, one simple step would be to reduce the quantity of the solvents we are using. The sustainability of the aminating reagent itself would need to be addressed,” said Zhukhovitskiy.

Scalability is another consideration. Though the method works efficiently in laboratory conditions, adapting it for industrial use will require further development.

The technique is also currently limited to rubber and other materials based on diene polymers like polybutadiene and polyisoprene.

“In its current form, it wouldn’t work on polyolefins for instance,” Zhukhovitskiy noted. “However, future work in our group is aimed at addressing exactly such questions.”

“While we have established the proof of the concept in our work, the process – including reactor design, reaction conditions and separation methods – will need to be optimized to make it more sustainable and scalable. Collaboration with chemical engineers will be crucial here, and of course it will not happen without appropriate funding to support this ambitious undertaking,” said Zhukhovitskiy.

Reference: Towell SE, Ratushnyy M, Cooke LS, Lewis GM, Zhukhovitskiy AV. Deconstruction of rubber via C–H amination and aza-Cope rearrangement. Nature. 2025. doi: 10.1038/s41586-025-08716-6

About the interviewee:

Dr. Aleksandr (Alex) V. Zhukhovitskiy is an assistant professor of chemistry and William R. Kenan Jr. Faculty Fellow at the University of North Carolina at Chapel Hill (UNC-Chapel Hill). Zhukhovitskiy completed his undergraduate studies in Chemistry, Mathematics and the Integrated Science Program at Northwestern University, earning a joint BA/MS degree in Chemistry in 2011. During the next five years, he conducted doctoral research in the laboratory of Professor Jeremiah A. Johnson in the Department of Chemistry at the Massachusetts Institute of Technology, and from 2016 till 2019, he was a postdoctoral research in Professor F. Dean Toste’s group in the Department of Chemistry at the University of California, Berkeley. In 2019, Alex started his research group in the Department of Chemistry at UNC-Chapel Hill.