Toxic Tire Decontamination: Researchers Demonstrate Ability to Remove Toxic Particles from Used Tires

Tires are an essential part of daily life. Without these, our vehicles would simply be a mass of assembled parts, convenient to sit on but ineffective at getting us to our destination.

While the usefulness of tires is undisputed, they do have some problems. According to a 2016 Federal Highway Administration report, 280 million tires are thrown away each year in the United States. Globally, this number is much higher – more than 1 billion people, according to a report by the World Business Council for Sustainable Development.

What to do with these end-of-life tires is an ongoing and often complex debate.

Tires are composite materials that contain many ingredients, including a molecule known as 6PPD, which protects the tire’s rubber from UV rays to make it last longer. 6PPD accomplishes this by absorbing sunlight and preventing the material from breaking down due to reaction with ozone and other active oxygen species in the air.

However, when tires wear out from contact with the road, 6PPD particles are released into the environment. Rainwater runoff carries these toxic particles into freshwater systems and other bodies of water, where even small amounts of the chemicals can quickly kill fish. Tribes in the Pacific Northwest recently petitioned the Environmental Protection Agency to consider enacting regulations to ban the use of this chemical.

Researchers from the University of Delaware’s Plastics Innovation Center and Department of Chemical and Biomolecular Engineering, led by Unidel Dunn Rich Energy Chair Dion Vlakos, have developed a method to tackle the decontamination of used tires from 6PPD.

Researchers recently published their approach in Nature Chemical Engineering to upgrade 6PPD to a safe chemical and convert leftover crumb rubber into an aromatic compound found in everything from pigments to cosmetics to electronics. We demonstrated a method to convert it into carbon black, a soot-like substance.

Safely reuse tire materials

Tires account for about a third of the microplastics in the environment, Vlachos said. This is because almost 25% of the tire parts are made of synthetic rubber, which is plastic.

When exposed to sunlight, 6PPD is converted into 6PPD-quinone, a so-called diketone, or a molecule composed of two ketone groups. One of the main sources of these diketone molecules is the tires themselves. Microplastics aren’t the only things that are created by the wear and tear of tires. These molecules can also be released into the environment from tires that are left in landfills and exposed to the elements.

“You can’t put a filter in the environment any more than you can put a filter in your home dryer to collect fibers,” says Vlakos, who is also director of the Delaware Energy Institute.

Other researchers in the field have attempted to use high heat to break down the tire material through a process known as pyrolysis, but 6PPD is stubborn and leaves diketone molecules in the oil left behind. When oil is used as a fuel or other material, problems arise because the diketone molecules migrate.

So the Vlachos team decided to try to remove 6PPD through a process known as chemical extraction. This involves placing millimeter-sized tires or crumb rubber into a classic microwave reactor, heating the material, and using a chemical solvent to quickly separate 6PPD from other molecules present.

Once the 6PPD molecules are removed, they can be chemically converted into safe chemicals that can be used or sold at low cost. Meanwhile, the rest of the tire can be recycled using traditional plastic recycling methods. This is an advantage given that there are currently no substitutes for tires in general. This allows the refurbished tire material to be safely used in practical applications such as soccer fields, playgrounds, and road asphalt.

Crumb rubber can also be used as an aromatic compound, a starting material for a wide range of consumer products, and as carbon black, a soot-like substance found in many pigments, conductive/insulating elements, and reinforcing materials, among others. .

The UD research team has been securing this new approach through the university’s Office of Economic Innovation and Partnerships.

To date, Vlachos said, the research team has proven this approach on a laboratory scale, and techno-economic analysis shows that the cost is very reasonable. Although this is a positive step, further work is needed and time is of the essence.

The number of used tires around the world continues to grow, with some reports estimating that up to 5 billion tires could be discarded worldwide by 2030. Meanwhile, scrap tire usage in the U.S. has decreased by 25% since 2013. And 2021.

“I think it’s important to actually recycle the tires themselves, so there’s a true circular solution to upcycling,” he said. “We have to make things outside of the lab, at a sufficient scale and at a reasonable cost. This has to be demonstrated in pilot-scale facilities. We are still doing that. No.”

Bringing solutions out of the lab and into the real world requires additional engineering effort and time. Having a dedicated Plastics Innovation Center at UD is a crucial advantage, Vlachos said, as it brings an important group of people to talk about, think about, and work on these issues. In addition to the automotive industry, startups and other talent will be key to driving solution adoption.

“We need to educate the community. We need social sensitivity, we need awareness. It’s not a problem that will be solved automatically,” Vlachos said.