Old tires recycled into valuable materials

March 27, 2025

Researchers have developed a novel chemical method to transform discarded rubber, including used tires, into valuable precursors for epoxy resins.

“Our research represents a paradigm shift in how we approach the problem of rubber waste,” said Sydney Towell, a co-author of the study.

The study, led by Dr. Aleksandr Zhukhovitskiy of the University of North Carolina at Chapel Hill, introduces a two-step process involving C–H amination and a polymer rearrangement strategy.

Rubber’s durable, cross-linked polymer structure, while beneficial in products like tires, makes it notoriously difficult to recycle. Current methods, such as devulcanization or polymer backbone cleavage, either weaken the material or produce low-value byproducts, failing to provide a viable, scalable recycling solution.

“Neither approach provides an efficient, scalable solution for repurposing rubber waste,” added the researchers in a press release.

However, the new method effectively breaks down the complex cross-linked structure of rubber into soluble amine-functionalized materials.

Breaking down rubber into functional materials

In a test using used rubber, the process achieved complete breakdown in just six hours, converting the waste into materials suitable for manufacturing epoxy resins.

This new technique addresses the critical environmental issue of rubber waste accumulation. 

In the US alone, over 274 million tires were discarded in 2021, with a significant portion ending up in landfills. 

Traditional recycling methods, like pyrolysis, pose health and environmental risks due to the production of harmful byproducts such as benzene and dioxins.

“Our research seeks to overcome these challenges by developing a method that breaks down rubber into functional materials that possess value even as a mixture,” said Dr. Zhukhovitskiy.

Process operates under mild conditions

The researchers utilized a sulfur diimide reagent to install amine groups at specific locations in the polymer chains. This set the stage for a backbone rearrangement that breaks down the rubber into usable materials.

 The process operates under mild conditions (95-122°F), making it more environmentally friendly and cost-effective compared to traditional methods.

“The efficiency of this method is particularly striking when compared to traditional recycling techniques, which often require extreme temperatures or expensive catalysts,” highlighted the team.

The resulting amine-modified poly-dienes can be used to create epoxy resins, which are widely used in adhesives, coatings, and composites and have strength comparable to commercial resins.

“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 resins,” said Maxim Ratushnyy, a co-author of the study.

Greener solvent for sustainability

The research also focused on the environmental impact, evaluating the process using the Environmental Impact Factor (E-factor). 

While the complete E-factor, including solvent use, was initially high, the simple E-factor, excluding solvents, was significantly lower, which indicates potential for further optimization. 

The team is now exploring greener solvent systems to enhance sustainability.

“By harnessing the power of C–H amination and backbone rearrangement, this method provides a new pathway to transforming post-consumer rubber into high-value materials, reducing reliance on landfills and minimizing environmental harm,” concluded Towell.