image credit to The National
By Samyukta Srinivasan
Plastic has proven itself to be one of the most useful and efficient materials to exist — that is, only until you no longer need it. The excessive amounts of dyes, filters, fillers, and flame retardants contained in plastics make it impossible for them to be recycled without a loss in their appearance or performance. Even the most recyclable plastic poly(ethylene terephthalate), also known as PET, can only be recycled at a rate of 20-30%, with the rest going into incinerators or landfills where the material takes centuries to decompose.
However, a workforce of researchers at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory has succeeded in designing a fully recyclable plastic that can be disassembled into its constituent parts at the molecular level, and then reassembled once again into a different shape, texture, and color indefinitely without a loss of performance or quality.
The new substance is called poly(diketoenamine), also known as PDK, as published in the journal Nature Chemistry.
Peter Christensen, lead author and postdoctoral researcher at Berkeley Lab’s Molecular Foundry said, “Most plastics were never made to be recycled, but we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.”
Christensen was a part of a multidisciplinary team led by Brett Helms, a staff scientist at Berkeley Lab’s Molecular Foundry. The co-authors of the Nature Chemistry Journal include Angelique Scheuermann and Kathryn Loeffler, who were undergraduate researchers at the time of the study.
All plastics are made up of large molecules called polymers, which in turn are composed of repeating units of shorter carbon- containing compounds called monomers.
According to researchers, the chemicals that are added to plastics to give them desirable traits — fillers for rigidity and plasticizers for elasticity, for example — bind to the monomers so tightly that they stay in the plastic even after it goes through the recycling process.
While being processed in recycling plants, plastics with different chemical compositions — such as stretchy, candy-colored, clear, and hard plastics — are ground into bits and mixed together. When the mixture of chopped-up plastics is melted to make a new material, it is difficult to predict which properties it will inherit from the original plastics.
This unpredictable inheritance of properties is what is holding plastic back from becoming a material whose monomers can be recovered for reuse for as long as possible, or be “upcycled” to make a new, higher quality product.
“Circular plastics and plastics upcycling are great challenges,” said Helms. “We’ve already seen the impact of plastic waste leaking into our aquatic ecosystems, and this trend is likely to be exacerbated by by the increasing amounts of plastics being manufactured and the downstream pressure it places on our municipal recycling infrastructure.”
The researchers believe that their new endlessly recyclable plastic will be able to serve as a good alternative to many non-recyclable plastics in use today.
“We’re at a critical point where we need to think about the infrastructure needed to modernize recycling facilities for future waste sorting and processing,” said Helms. “If these facilities were designed to recycle or upcycle PDK and related plastics, then we would be able to more effectively divert plastic from landfills and the oceans. This is an exciting time to start thinking about how to design both materials and recycling facilities to enable circular plastics,” he added.
The researchers plan to build on this by developing PDK plastics with a wide range of thermal and mechanical properties for various applications including textiles, 3D printing, and foams. In addition, they are also looking to incorporate plant-based materials and other sustainable sources.