News Release


Scientists from Berkeley Lab have made a next-generation plastic that can be recycled again and again into new materials of any color, shape, or form

Peer-Reviewed Publication

DOE/Lawrence Berkeley National Laboratory

PDK Plastic


Credit: Peter Christensen et al./Berkeley Lab

Light yet sturdy, plastic is great - until you no longer need it. Because plastics contain various additives, like dyes, fillers, or flame retardants, very few plastics can be recycled without loss in performance or aesthetics. Even the most recyclable plastic, PET - or poly(ethylene terephthalate) - is only recycled at a rate of 20-30%, with the rest typically going to incinerators or landfills, where the carbon-rich material takes centuries to decompose.


"Most plastics were never made to be recycled," said lead author 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."

Christensen was part of a multidisciplinary team led by Brett Helms, a staff scientist in Berkeley Lab's Molecular Foundry. The other co-authors are undergraduate researchers Angelique Scheuermann (then of UC Berkeley) and Kathryn Loeffler (then of the University of Texas at Austin) who were funded by DOE's Science Undergraduate Laboratory Internship (SULI) program at the time of the study. The overall project was funded through Berkeley Lab's Laboratory Directed Research and Development program.


According to the researchers, the problem with many plastics is that the chemicals added to make them useful - such as fillers that make a plastic tough, or plasticizers that make a plastic flexible - are tightly bound to the monomers and stay in the plastic even after it's been processed at a recycling plant.

During processing at such plants, plastics with different chemical compositions - hard plastics, stretchy plastics, clear plastics, candy-colored plastics - are mixed together and ground into bits. When that hodgepodge of chopped-up plastics is melted to make a new material, it's hard to predict which properties it will inherit from the original plastics.

This inheritance of unknown and therefore unpredictable properties has prevented plastic from becoming what many consider the Holy Grail of recycling: a "circular" material whose original monomers can be recovered for reuse for as long as possible, or "upcycled" to make a new, higher quality product.

So, when a reusable shopping bag made with recycled plastic gets threadbare with wear and tear, it can't be upcycled or even recycled to make a new product. And once the bag has reached its end of life, it's either incinerated to make heat, electricity, or fuel, or ends up in a landfill, Helms said.

"Circular plastics and plastics upcycling are grand challenges," he said. "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."

Recycling plastic one monomer at a time

The researchers want to divert plastics from landfills and the oceans by incentivizing the recovery and reuse of plastics, which could be possible with polymers formed from PDKs. "With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively," Helms said.


"We're interested in the chemistry that redirects plastic lifecycles from linear to circular," said Helms. "We see an opportunity to make a difference for where there are no recycling options." That includes adhesives, phone cases, watch bands, shoes, computer cables, and hard thermosets that are created by molding hot plastic material.

The researchers first discovered the exciting circular property of PDK-based plastics when Christensen was applying various acids to glassware used to make PDK adhesives, and noticed that the adhesive's composition had changed. Curious as to how the adhesive might have been transformed, Christensen analyzed the sample's molecular structure with an NMR (nuclear magnetic resonance) spectroscopy instrument. "To our surprise, they were the original monomers," Helms said.


Next, they proved that the recovered PDK monomers can be remade into polymers, and those recycled polymers can form new plastic materials without inheriting the color or other features of the original material - so that broken black watchband you tossed in the trash could find new life as a computer keyboard if it's made with PDK plastic. They could also upcycle the plastic by adding additional features, such as flexibility.

Moving toward a circular plastic future


"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," said Helms.



The Molecular Foundry is a DOE Office of Science User Facility that specializes in nanoscale science.

This work was supported by the DOE's Laboratory Directed Research and Development (LDRD) program with additional funding provided by the DOE Office of Science through the SULI program.



