Epoxy resins are coatings and adhesives used in a broad range of familiar applications, such as construction, engineering and manufacturing. However, they often present a challenge to recycle or dispose of responsibly. For the first time, a team of researchers, including those from the University of Tokyo, developed a method to efficiently reclaim materials from a range of epoxy products for reuse by using a novel solid catalyst.
There's a high chance you are surrounded by epoxy compounds as you read this. They are used in electronic devices due to their insulating properties; clothing such as shoes due to their binding properties and physical robustness; building construction for the same reason; and even in aircraft bodies and wind turbine blades for their ability to contain strong materials such as carbon fibers or glass fibers. It's hard to overstate the importance of epoxy products in the modern world. But for all their uses, they inevitably have a downside: Epoxy compounds are essentially plastics and prove difficult to deal with after their use or at the end of the life of an epoxy-containing product.
"For example, to decompose fiber-reinforced plastics, perhaps used in aircraft parts, you'd need high temperatures over 500 degrees Celsius, or strong acid or base conditions. These things have an energy cost, and the harsh conditions can damage the fibers and things you might be trying to recover," said Associate Professor Xiongjie Jin at the University of Tokyo. "To deal with this problem, a relatively new process called catalytic hydrogenolysis shows promise, but existing catalysts for this are not reusable as they dissolve in the solvent in which the epoxy decomposition takes place. So, we created a new solid catalyst which is easily recoverable and reusable."
Jin and Professor Kyoko Nozaki, both from the Department of Chemistry and Biotechnology, and their team developed an efficient and robust catalyst to decompose epoxy compounds into carbon fibers, glass fibers and phenolic compounds, which are important raw materials in the chemical industry. The catalyst is referred to as bimetallic as it uses two metals, nickel and palladium, which are supported on cerium oxide and work together to mediate reactions between epoxy resins and hydrogen gas. Though the reaction temperature needs to be at around 180 degrees Celsius, the energy requirements are far lower than those needed to create 500-degree conditions, and the lower temperatures mean recovered materials can be reused.
"We were pleased to see experimental results that closely matched our expectations about how this process would work, but we were nicely surprised when we realized the catalyst could be reused at least five times without any reduction in its performance," said Jin. "As our catalyst is effective at cleaving carbon-oxygen bonds, with modification, it might even work with other plastics as well, as they contain those bonds too."
The team is now keen to explore ways to improve its methods and materials, though, as it may still take some development to make it a more commercially viable option.
"Although our catalyst does not require such high temperatures, there is still room for improvement in the environmental impact of the solvent we are currently using," said Nozaki. "We would also like to bring the cost down by finding a catalyst that does not contain a precious metal such as palladium. It might also be possible to increase the range of materials which could be recovered from various epoxy compounds, reducing the environmental overheads of these incredibly versatile and useful plastics."
