Plastic is a cheap and versatile material so it’s no wonder it has become so widely used. The trouble, of course, is that it’s also very durable and not easily recyclable so most of it ends up as waste, causing massive harm to the environment.
Research indicates that not even biodegradable plastics are all that environmentally friendly. The solution then is to stop using plastic products or at least to do so far more sparingly.
Science can also help. A case in point: researchers at the Lawrence Berkeley National Laboratory of the U.S. Department of Energy have come up with a new form of plastic polymer that can be disassembled and then reassembled with relative ease.
Plastics are made of polymers, chains of hydrogen and carbon, which are derived from substances like petroleum. Their web of molecules can be mixed with a range of chemicals to achieve a variety of different properties, which is what makes plastics so versatile. Some plastics can be broken down into their components, which makes them easy to recycle. Other plastics like thermoset polymers, however, are generally far harder to recycle.
“Most plastics were never made to be recycled,” says Peter Christensen, a chemist at the lab in Berkeley who was an author of a new study in the journal Nature Chemistry. “But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.”
The lab’s team managed to make durable thermoset polymers recyclable by tinkering with their monomer components known as diketoenamine. They condensed these simple building blocks into newly created polydiketoenamine (PDK) bonds, which can easily be dissolved just by soaking them in a strong acid bath for a few hours.
“It’s a click reaction that works at room temperature, without needing catalysts, additives or even a solvent,” says Brett Helms, the team’s leader. “They just require a few minutes in a ball mill.”
Once the polymers are broken down, their core parts can be separated from additives repeatedly in a closed-loop cycle, the researchers say. To test this recovery process, they contaminated PDK and acid solutions with substances such as flame-retardant chemicals since many plastics contain such additives. The scientists found that these additives did not meaningfully change their recovery method.
This means that the end result is a plastic ingredient that is shorn of colors and chemical agents. It can therefore repurposed into another product. “We’re interested in the chemistry that redirects plastic lifecycles from linear to circular,” Helms says. “We see an opportunity to make a difference for where there are no recycling options.”
“The approach is innovative and elegantly simple,” notes Rachel O’Reilly, a chemist specializing in polymer science at the University of Birmingham. “This new type of plastic can undergo closed loop recycling, which means it can be depolymerised into its monomers,” she adds, “and then remade into a polymer with the same properties as the original.”
