A recent study highlights a method to lessen the environmental damage caused by tires after they’ve served their purpose. The innovative technique transforms 6PPD, a beneficial yet ecologically harmful molecule that enhances tire durability, into harmless chemicals.
Researchers from the University of Delaware have created a technique to reduce the pollutants emitted from tires once they reach the end of their life cycle.
This study, published in Nature Chemical Engineering, reveals how the team can convert 6PPD, a molecule that shields tires from UV rays and extends their lifespan, into safe chemicals. Additionally, the leftover crumb rubber can be transformed into valuable substances like aromatics and carbon black, a soot-like material used in various industries, including pigments, cosmetics, and electronics. Dion Vlachos, the chair of UD’s Department of Chemical and Biomolecular Engineering, led the study with collaboration from the University’s Center for Plastics Innovation.
Vlachos stated that tires contribute to approximately one-third of the microplastics found in our environment. This is largely due to the fact that around 25% of tire composition consists of synthetic rubber, a type of plastic.
When exposed to sunlight, 6PPD changes into 6PPD-quinone, which is referred to as a diketone, a molecule that includes two ketone groups. Tires are a significant source of these diketone molecules. Moreover, the environmental impact isn’t limited to microplastics; these substances can also be released from tires disposed of in landfills and exposed to weather conditions, like rain.
“You can’t install a filter in the environment like you might do to capture fibers from your household dryer,” emphasized Vlachos, who is also the director of the Delaware Energy Institute.
Previous efforts to decompose tire materials with high heat, a technique known as pyrolysis, have struggled with 6PPD; the diketone molecules tend to remain in the extracted oil. If this oil is utilized for fuel or other substances, the diketone molecules travel along, presenting an issue.
Consequently, Vlachos’s team opted for a strategy to eliminate 6PPD by employing a method called chemical extraction. This involved placing small pieces of tire, known as crumb rubber, into a conventional microwave reactor. The materials were heated, and a chemical solvent was used to effectively separate the 6PPD from the other molecules present.
After extracting the 6PPD molecules, they can be chemically transformed into safe substances that can be manufactured or sold at a nominal cost. The remaining tire material can be recycled through traditional plastic recycling methods, which is particularly beneficial since there are currently no alternative solutions for tires. This approach would allow the processed tire elements to be utilized in various practical applications, such as on soccer fields, playgrounds, or in road construction without concerns over safety. Additionally, the crumb rubber could serve as a source for aromatics, essential components in a variety of consumer goods, or as carbon black, which functions in many pigments and as conductive/insulating materials, among other uses.
The research team has safeguarded their innovative methodology through the Office of Economic Innovation and Partnerships at the University.
So far, the team has validated this approach on a laboratory scale, according to Vlachos, and a technoeconomic analysis indicates that the costs appear to be quite manageable. Although this is a promising development, further work is necessary and time is of the essence.
Globally, the number of discarded tires is increasing, with some estimates suggesting that by 2030, up to five billion tires may be in need of disposal. Meanwhile, the use of scrap tires in the U.S. has decreased by 25% from 2013 to 2021.
“It’s crucial to actually recycle the tire itself for true circular solutions that promote upcycling,” he stated. “We need to produce these solutions at a significant scale and at a reasonable cost outside the laboratory. This needs to be demonstrated with pilot-scale facilities, which we haven’t done yet.”
Moving solutions from the lab to practical use will require additional engineering efforts and time. Vlachos noted that having a dedicated Center for Plastics Innovation at UD is a significant asset because it fosters a group of people focused on exploring and addressing these challenges. Collaboration with startups and other innovators, together with the automotive sector, will be vital for advancing solutions to implementation.
“We must educate the community. There needs to be social sensitivity and greater awareness. This is not an issue that will resolve itself,” Vlachos remarked.
Co-authors of the paper include Sean Najmi, Pooja Bhalode, Montgomery Baker-Fales, Brandon Vance, Esun Selvam, Kewei Yu, and Weiqing Zheng.
