A U.S. Department of Energy-funded study, “Deconstruction of Rubber via C-H Amination and Aza-Cope Rearrangement,” recently published in Nature and led by Dr. Aleksandr Zhukhovitskiy, William R. Kenan, Jr. Fellow and Assistant Professor in the Department of Chemistry at UNC-Chapel Hill, introduces a novel chemical method for breaking down rubber waste. This pioneering technique utilizes C-H amination and a polymer rearrangement strategy to transform discarded rubber into valuable precursors for epoxy resins, offering an innovative and sustainable alternative to traditional recycling methods.

Rubber, including the synthetic kind used in tires, is composed of polymers cross-linked together into a three-dimensional network that behaves as a tough, flexible material. Recycling these materials is difficult due to the extensive cross-linking within the polymer structure, which gives rubber its durability but also makes it resistant to degradation. Traditional methods for breaking down rubber focus on two main approaches: de-vulcanization, which breaks sulfur cross-links but weakens the polymer’s mechanical properties, and cleavage of the polymer backbones using oxidative or catalytic methods, which often result in complex, low-value byproducts. Neither approach provides an efficient, scalable solution for repurposing rubber waste.

“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, who is the corresponding author of the study.

The researchers introduce a sulfur diimide reagent that enables the installation of amine groups at specific locations in the polymer chains. This step is crucial because it sets the stage for the subsequent backbone rearrangement. This chemical reaction reorganizes the polymer backbone, breaking down the rubber into soluble amine-functionalized materials that can be used to produce epoxy resins.

The researchers showed that their two-step process works very well. In a test with a model polymer, they broke it down significantly, reducing its molecular weight from 58,100 g/mol to about 400 g/mol. When they applied the method to used rubber, it broke down completely in just six hours, turning it into a soluble material with amine groups that could be used to manufacture broadly useful materials like epoxy resins.

The efficiency of this method is particularly striking when compared to traditional recycling techniques, which often require extreme temperatures or expensive catalysts. The researchers achieved their results under mild conditions (35-50°C, or 95-122°F) in aqueous media, making the process more environmentally friendly and cost-effective.

Epoxy resins are widely used in industries for adhesives, coatings, and composites. They are usually made from petroleum-based chemicals like bisphenol A and curing agents. This research shows that amine-modified poly-dienes, produced using the researchers’ method, can create epoxy materials with strength similar to commercial resins.

“In moments like this I come to appreciate the power of organic synthesis,” said Maxim Ratushnyy, a co-author of the paper and former postdoctoral scholar at UNC-Chapel Hill. “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.”

Beyond its practical applications, this study marks a significant step toward greener recycling technologies. The researchers evaluated the environmental impact of their process using the Environmental Impact Factor (E-factor), a measure of waste generated relative to the product yield.

“E-factor is a simple but powerful metric to compare the impact of a new process to incumbents, but also to highlight process steps that can be improved as we work to transition this process out of the lab and into practice,” said Dr. Geoff Lewis, a research specialist at the University of Michigan’s Center for Sustainable Systems.

While the complete E-factor, which includes solvent use, was high, the simple E-factor, excluding solvents, was much lower, highlighting areas where the process could be further optimized for sustainability. The team is already exploring greener solvent systems and alternative reaction conditions to reduce waste generation.

“Our research represents a paradigm shift in how we approach the problem of rubber waste,” said Sydney Towell, a co-author of the study and Ph.D. candidate at UNC-Chapel Hill. “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.”

Obesity is considered to be a global public health concern, but experts still disagree about the precise origins and causes of rising obesity rates. One topic under debate is whether a person’s individual genetics and behaviors are more or less important than environmental factors, like socioeconomic status, in developing obesity.

In the new study, researchers estimated the impact of several factors on a person’s weight, including societal factors, like a person’s job type, as well as early life factors, like a person’s birth order, how they were delivered and whether their mother smoked or was obese. They looked specifically at whether a person was overweight, obese or severely obese at age 16 and age 42. They also looked at participants’ weight between ages 16 to 42, a range that spans the rise in obesity rates in the United Kingdom. The data came from the 1958 National Child Development Study, a long-term study that followed the lives of more than 17,000 people born in a single week in March 1958 across England, Scotland and Wales.

The analysis showed that if a mother was obese or if she smoked, her child was more likely to be obese or severely obese at each of the ages examined. The findings demonstrate that these early life factors can have a persistent effect on a person’s weight. Notably, these factors were just as powerful before and after the start of the rise in obesity rates in the UK, suggesting that the impact of individual factors, like behaviors, likely did not change during that time.

The results suggest that societal and early-life risk factors could be used to target obesity prevention programs for children and adults. The researchers also conclude that, since individual risk factors have not changed as obesity rates have risen, new studies are needed to identify societal factors that may have caused the current obesity pandemic.

The authors add: “Our research shows that the effect of maternal influences persists through to age 42 and that strikingly, those predictors were just as powerful (and prevalent) in the era before the current obesity pandemic began. This suggests that, as Geoffrey Rose pointed out, novel studies are needed of factors at the community/societal level that may have caused the current obesity pandemic, since individual-level risk factors appear not to have changed over the time period spanning the pandemic’s onset and growth.”