Even if everyone was able to figure out the recycling codes stamped on the bottom of their yogurt containers and get all their plastic bottles in the big blue bins, there’s still a pretty high chance that most of their plastic waste would ultimately end up in a landfill or incinerator instead of a being turned into playground bench. That’s because many plastics simply can’t be reused due to additives mixed with in with them. But a new material developed at Lawrence Berkeley National Laboratory may eventually be a solution, allowing plastics to be recycled over and over again.
Understanding how the new process works means understanding a little bit about the chemistry of plastic. Most plastics are made of polymers, chains of hydrogen and carbon which are chiefly derived from petroleum products like crude oil. Polymers are composed of shorter strands called monomers. To give plastics certain characteristics like toughness, flexibility or color, certain chemicals are added which from strong bonds with the monomers.
While many polymers are thermoplastic, meaning they can be melted down and reused, the additives bonded to them can interfere with the process. So when plastics are ground up and mixed together for recycling, all those additives make the final product unpredictable and lower quality. That’s why most recycled plastic is “downcycled” or turned into items like handbags or benches instead of completing the recycling loop by becoming milk jugs, water bottles and Greek yogurt tubs.
“Most plastics were never made to be recycled,” Peter Christensen at the Berkeley Lab and lead author of the new study in Nature Chemistry says in a press release. “But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.”
Polydiketoenamine, or PDK,
Christensen and his team discovered that one type of polymer, called polydiketoenamine, or PDK, can be successfully separated from additives after it is dunked in a highly acidic solution which leaves behind the original monomers. Further testing showed that these reclaimed monomers are high quality enough that they can be used to produce high quality plastic. Instead of being “downcycled,” the PDK can be “upcycled,” closing the recycling loop.
The researchers now hope to develop various PDK-based plastics for things like foams, textiles and other applications. The hope is that recycling facilities could also be upgraded to process the new plastic. “[This] could significantly reduce the leakage of plastics into the environment,” Jon Schlosberg, senior researcher on the project, tells at ABC News. “That broken black watchband you tossed in the trash could find new life as a computer keyboard if it’s made with our PDK plastics.”
Currently, however, the recyclable PDK has only been recycled in the lab, and the team has not tested it at an industrial scale. But it’s not the only polymer that may improve plastics recyclability. Last year, researchers at Colorado State University announced the discovery of an “infinitely” recyclable polymer that can be turned into plastic and then turned back into monomers using a catalyst.
While these “greener” plastics will hopefully help reduce plastic pollution in the future, humanity still needs to deal with the ۱۸ billion pounds of conventional plastic that get into our oceans each year and the 6,300 million metric tons of plastic created since 1950. According to a study last year, 79 percent of that waste is still with us, floating in the sea, sitting in landfills or scattered across the countryside.