Today, over one billion car tyres are produced every year. The number in use is forecast to increase by up to 60% in 2021, as the number of vehicles on the roads rise. Made from synthetic rubber, there are certainly more ways that they could become more environmentally friendly. Conventional tyres are predominantly made from fossil fuels with very few options in place to dispose of them. The UK sends 26% of its tyres to landfill, but this is still far less than some other EU countries; France sends almost half to landfill whilst Spain sends 58% to pile up in designated sites. And if they aren't recycled then they are burnt as a "replacement fuel" in the manufacturing of cement. This has become a common way to dispose them, but it is continuing to concern environmentalists and scientists, particularly those at the University of Minnesota. Scientists there have responed to the growing problem by inventing a renewable car tyre produced from natural resources probably found in your back garden. These tyres which can be made from biomass formed by trees and grass would be identical to existing car tyres with the same chemical makeup, colour, shape, and performance.
Although tyres remain intact for decades, some of their components can break down and spill out into the environment. In the manufacturing process, toxic additives such as zinc, chromium, lead, copper, cadmium and sulphur are used. This means that the only other sustainable alternative is to retread them but this is expensive. By contrast, the team at the University of Minnesota have “created a new chemical process to make isoprene, the key molecule in car tyres, from natural products like trees, grasses, or corn,” said Paul Dauenhauer, an associate professor of chemical engineering and materials science and lead researcher of the study. “This research could have a major impact on the multi-billion dollar automobile tyres industry.”
The Office for Technology Commercialisation at the University of Minnesota has applied for a patent on the renewable rubber technology and plans to license the technology to companies interested in commercialising the technology. Isoprene is produced by thermally breaking apart molecules in petroleum that are similar to gasoline in a process called “cracking.” The isoprene is then separated out of hundreds of products and purified. In the final step, the isoprene is reacted with itself into long chains to make a solid polymer that is the major component in car tires.
Biomass-derived isoprene has been a major initiative of tyre companies for the past decade, with most of the effort focused on fermentation technology (similar to ethanol production). However, renewable isoprene has proven a difficult molecule to generate from microbes, and efforts to make it by an entirely biological process have not been successful.
“Economically bio-sourced isoprene has the potential to expand domestic production of car tyres by using renewable, readily available resources instead of fossil fuels,” said Frank Bates, a world-renowned polymer expert and University of Minnesota Regents Professor of Chemical Engineering and Materials Science. “This discovery could also impact many other technologically advanced rubber-based products.”
Funded by NSF, researchers from the Centre for Sustainable Polymers have focused on a new process that begins with sugars derived from biomass including grasses, trees and corn. They found that a three-step process is optimized when it is “hybridised,” meaning it combines biological fermentation using microbes with conventional catalytic refining that is similar to petroleum refining technology.
The first step of the new process is microbial fermentation of sugars, such as glucose, derived from biomass to an intermediate, called itaconic acid. In the second step, itaconic acid is reacted with hydrogen to a chemical called methyl-THF (tetrahydrofuran). This step was optimized when the research team identified a unique metal-metal combination that served as a highly efficient catalyst.
“Collaboration was really the key to this research taking biomass all the way to isoprene,” said Carol Bessel, the deputy director for the chemistry division at the National Science Foundation (NSF), which funds the Centre for Sustainable Polymers. “This collaboration and synergy among researchers with different approaches and skills is really what we are trying to promote within the NSF Centres for Chemical Innovation Program.”
To hear about more breakthrough technologies you might like to read: