"Molecular scissors" break bonds in old tires for easier recycling
Finding new uses for discarded tires is challenging, in part because of the sheer number the world churns through every day but also because of the inherent difficulties in recycling them. Scientists have now come up with a new way to break apart key components from the tire material for re-use, which could provide the basis for new and improved recycling methods.
Around three billion car tires were manufactured and sold around the world in 2019, according to researchers at Ontario's McMaster University. Most of those will eventually wind up in landfill or other facilities, where they can leach harmful contaminants into the environment, or spew harmful toxins into the air if set alight.
While there are ways to turn some chemical components of old tires into building blocks for asphalt and cement, and scientists have made progress towards other second-life products such as clean fuels or improved concrete, some parts are unretrievable.
More specifically, a standard method of recovering the petroleum-based polymers from tires for re-use has remained elusive. This is because of the strong bonds that are created during the curing process, where sulfur is mixed with natural rubbers to create bridges between the natural polymers to turn the liquid to a solid material.
“The chemistry of the tire is very complex and does not lend itself to degradation – for good reason,” says Michael Brook, a professor in the Department of Chemistry & Chemical Biology at McMaster and lead author of the study. “The properties that make tires so durable and stable on the road also make them exceptionally difficult to break down and recycle.”
Brooks and his team have developed what he describes as "molecular scissors," which work by breaking down the bonds and dissolve the rubber material, leaving disassembled components that can be turned into new products more easily.
“We have found a way to cut all the horizontal lines so instead of having a net, you now have a large number of ropes, which can be isolated and reprocessed much more easily,” Brooks says.
The scientists note that the research is still in its early stages and the technique is currently far too expensive to be scaled up for industrial applications. But the breakthrough is promising, and they will now work on making it more cost-effective with a view to wider applications.
“We’re working on it, but this is the first major step," Brook says. "This process closes the loop on automotive rubber, allowing old tires to be converted into new products.”
The research was published in the journal Green Chemistry, while you can hear from Brooks in the video below.
Source: McMaster University