It’s a problem that has rolled along ever since the invention of the automobile: what to do with a car’s rubber tires once they wear out.
But first, to understand the magnitude of the problem, you’ll need a little car tire 101.
There are three main components in tires. First is the rubber, which improves contact between the tire and the road. The second is carbon black powder, which helps make the tire more durable. And the third is a metal, which supports the tire structure.
All of that is used to create a lot of tires. A 2008 report by the Tire Industry Project for the World Business Council for Sustainable Development says one billion “end-of-life” tires (tires too worn to be used) are generated every year. In the U.S. alone, over 274 million tires are discarded each year, with many ending up in landfills.
This waste not only fills landfills, but it also poses environmental hazards as toxic chemicals leach from the tires. There’s an additional risk of the tires catching fire, which releases toxic smoke and creates more leaching problems.
One method to avoid these hazards is to shred discarded tires into synthetic mulch. There’s also a process called pyrolysis that uses high temperatures to separate and recycle the metal, recover the carbon black powder and chemically recycle the rubber. However, it’s an energy-intensive process that creates benzene and dioxins, harmful chemicals that pose health and environmental concerns.
But there could be another way. Researchers at UNC-Chapel Hill have developed a groundbreaking recycling approach that appears to offer a cleaner, more sustainable solution.
“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 Aleksandr Zhukhovitskiy, Ph.D., associate chemistry professor at UNC-Chapel Hill, in an article about the discovery.
Rubber, including the synthetic kind in tires, is made up of polymers cross-linked into a 3D network that creates a tough yet flexible material. A polymer is a substance composed of very large molecules. Wool, starches and natural rubber are examples of natural polymers. Rayon, silicone and polyester are synthetic polymers.
That cross-linking of the polymer structure is what makes rubber so durable, but it also makes it difficult to recycle. Zhukhovitskiy’s lab focused on creating a low-energy chemical method to change the structure of polymers, breaking them down and transforming them into useful industrial materials.
The technique adds sulfur diimide into the material, creating a pathway to break the polymer structures into smaller, soluble pieces. What’s produced can then be used to create materials like high-strength epoxy resins, liquids used in coatings, adhesives and composites. The study found that resins produced with this experimental method would have similar strength to commercial resins.
In addition to offering an innovative and sustainable alternative to traditional recycling, researchers say their process of completely breaking down the rubber only took about six hours. The efficiency of the new process is important because traditional recycling techniques can require super-high temperatures and expensive catalysts. The team achieved their results at lower temperatures (95°F–122°F) and in a water-based solution, which is both environmentally friendly and cost-effective.
“Our research represents a paradigm shift in how we approach the problem of rubber waste,” said Sydney Towella coauthor of the study and Ph.D. candidate at UNC-Chapel Hill. “[T]his method provides a new pathway to transforming post-consumer rubber into high-value materials, reducing reliance on landfills and minimizing environmental harm.”
The study was funded by the U.S. Department of Energy and published in Nature.
Watch this video from Sci NC to learn how a North Carolina company has created plant-based, compostable plastics.
Plantswitch, an NC startup company, has created a plant-based, bioplastic resin to replace plastic.