Researchers at the United States Department of Energy’s (DOE) Lawrence Berkeley National Laboratory have formulated a plastic that can be recycled from the inside out. The new plastic can be broken down into individual molecules and then reassembled into different shapes or textures again and again without loss of integrity.
Plastic products often contain additives such as dyes, plasticisers and flame retardants which make it difficult to recycle them without a loss in quality. These additives bond to the plastic molecule chains and when the plastic is recycled, these bonds are weakened or broken. However, this new type of plastic, called polydiketoenamine (PDK), is about to change the way we recycle plastic products.
“Most plastics were never made to be recycled,” says Peter Christensen, a postdoctoral researcher at Berkeley Lab’s Molecular Foundry. “But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective.”
Traditional recycling methods affect quality of plastic
The current recycling process of plastic products changes the performance and quality of the product. Plastics with different chemicals and additives are mixed together and ground into small pellets. These batches of multicolored plastic bits are then melted and shaped into new products, but this recycled plastic inherits various qualities from the original plastic materials.
This inheritance can lead to unknown and unpredictable properties that prevent recycled plastic from being a truly circular material. The more times plastic gets recycled, the lower the quality of the resulting product. This means that recycling plastic does have a limit; once recycled plastic has reached this limit, it is incinerated or sent to a landfill.
“Circular plastics and plastics upcycling are grand challenges,” says lead researcher and staff scientist at Berkeley Lab’s Molecular Foundry, Brett Helms. “We’ve already seen the impact of plastic waste leaking into our aquatic ecosystems, and this trend is likely to be exacerbated by the increasing amounts of plastics being manufactured and the downstream pressure it places on our municipal recycling infrastructure,” he adds.
Recycling plastic at a molecular level
The research team at Berkeley Lab developed PDK plastic with the intention of keeping recycled plastic out of landfills and the oceans. Complete circular recycling has been made possible with PDK plastic. “With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively,” explains Helms.
Unlike conventional plastics, PDK can be broken down into molecular chains and freed from chemical additives by immersing the plastic in an acidic solution. The acid helps to break the bonds between the PDK molecules and any dyes, plasticisers and flame retardants – allowing pure chains of PDK molecules to be reassembled into a raw product without interfering qualities of the original plastic product.
“We’re interested in the chemistry that redirects plastic lifecycles from linear to circular,” says Helms. “We see an opportunity to make a difference for where there are no recycling options,” he explains. PDK plastic can be used to manufacture phone cases, watch straps, computer cables, shoes and hard molded plastic products.
This breakthrough could mean that PDK plastic will become the best alternative to non-recyclable and recyclable plastics with limited lifespans. However, recycling facilities need to be upgraded and modernised before PDK plastic can be processed on-site.
“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,” exclaims Helms.
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