Plastic fantastic: NMR aids recycling

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  • Published: May 15, 2019
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Plastic fantastic: NMR aids recycling

Avoiding landfill and incineration

Nuclear magnetic resonance (NMR) spectroscopy has been used in the development of a new type of plastic, poly(diketoenamine) or PDK, that can be recycled  repeatedly by breaking it down into its building blocks and repolymerising into a new products with a different shape, texture, and colour without loss of performance or quality. (Photo by David Bradley(

Nuclear magnetic resonance (NMR) spectroscopy has been used in the development of a new type of plastic, poly(diketoenamine) or PDK, that can be recycled repeatedly by breaking it down into its building blocks and repolymerising into a new products with a different shape, texture, and colour without loss of performance or quality. The new polymer was developed by a team of researchers at the US Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab). Details are reported in the journal Nature Chemistry.

"Most plastics were never made to be recycled," explains lead author on the paper 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." Only 20 to 30 percent of the most recyclable plastic, PET - or poly(ethylene terephthalate) - is recycled; most of it is typically incinerated or sent to landfill, and as is well known both of those endpoints can have worrying environmental implications.

Circular upcycling

The researchers point out that the thing that precludes the facile recycling of polymers is the presence of fillers for toughening the plastic product, or plasticizers that make them flexible. These additives are usually incorporated into the overall chemical structure of the material and cannot easily be removed to allow recycling. Indeed, the picture is worse for many recycling plants simply mix all plastics together whether hard, stretchy plastics, clear plastics, coloured plastics and then grind the resulting mixture into a powder that can be melted or further processed but has none of the benefits of a pristine polymer product. Of course, some recycling centres utilize spectroscopy and computer-controlled separation to segregate the different plastic shards prior to grinding, but sites with such facilities are expensive to build and run and limited in number and simply cannot address the vast deluge of waste plastics.

A "circular" material whose original monomers can be recovered for reuse again and again would be the ideal polymer, ready to be upcycled when the original product is collected for recycling at end of life.

Drastic plastic

"Circular plastics and plastics upcycling are grand challenges," says team leader 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 that with their PDKs, "the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively." NMR spectroscopy revealed exactly how the monomers were released. This would allow recovery and release from any additives. The team foresees the use of PDKs for mobile phone cases, watch straps, shoes, computer cables, and many other products, even adhesives.

Related Links

Nature Chem 2019, online: "Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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