A revolutionary discovery recycles plastic from the inside out



Peter Christensen et al./Berkeley Lab

Unlike conventional plastics, PDK plastic monomers could be recovered and released from any compound additive by simply submerging the material in a highly acidic solution.

Lightweight but tough, the plastic is excellent, until you no longer need it. Because plastics contain various additives, such as dyes, fillers or flame retardants, very few plastics can be recycled without loss of performance or aesthetics. Even the most recyclable plastic, PET (or poly (ethylene terephthalate)) is only recycled at a rate of 20-30%, and the rest usually goes to incinerators or landfills, where the carbon-rich material takes centuries to decompose .

Now, a team of researchers from the Lawrence Berkeley National Laboratory of the US Department of Energy (Berkeley Lab) has designed a recyclable plastic that, like a Lego set, can be disbadembled into its constituent parts at the molecular level, and then back To bademble in a different shape, texture and color again and again without loss of performance or quality. The new material, called poly (digotoenamine) or PDK, was published in the journal. Chemistry of Nature.

"Most plastics were never made to be recycled," said lead author Peter Christensen, a postdoctoral researcher at Berkeley Lab's Molecular Foundry. "But we've discovered a new way to bademble plastics that takes recycling into account from a molecular".

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

All plastics, from water bottles to auto parts, are made up of large molecules called polymers, which are composed of repetitive units of shorter carbon-containing compounds called monomers.

According to the researchers, the problem with many plastics is that the chemicals added to make them useful, such as the fillers that make a plastic hard or the plasticizers that make a plastic flexible, are tightly bound to the monomers and remain in the plastic even after. It has been processed in a recycling plant.

During processing in these plants, plastics with different chemical compositions (hard plastics, elastic plastics, transparent plastics, caramel-colored plastics) are mixed and ground into pieces. When that mixture of cut plastic melts to create a new material, it is difficult to predict what properties it will inherit from the original plastics.

This heritage 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 "Recycled" to make a new one. Higher quality product

Then, when a reusable shopping bag made of recycled plastic wears away with wear, it can not be recycled or recycled to make a new product. And once the bag has reached the end of its useful life, it is incinerated to produce heat, electricity or fuel, or ends up in a landfill, Helms said.

"Circulating plastics and recycling plastics are big challenges," he said. "We have already seen the impact of plastic waste seeping into our aquatic ecosystems, and this trend is likely to be aggravated by the increasing amounts of plastics being manufactured and the downstream pressure it exerts on our municipal recycling infrastructure." .

Recycling plastic one monomer at a time

Researchers want to divert plastics from landfills and oceans, encouraging the recovery and reuse of plastics, which could be possible with polymers formed from PDK. "With the PDK, the immutable links of conventional plastics are replaced with reversible links that allow the plastic to recycle more effectively," said Helms.

Unlike conventional plastics, PDK plastic monomers could be recovered and released from any compound additive by simply submerging the material in a highly acidic solution. The acid helps break down the bonds between the monomers and separates them from the chemical additives that give appearance and feel to the plastic.

"We are interested in chemistry that redirects the life cycles of plastic from linear to circular," said Helms. "We see the opportunity to make a difference where there are no recycling options." This includes adhesives, phone cases, watch straps, shoes, computer cables and hard thermosets that are created when molding hot plastic material.

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

After testing several formulations in Molecular Foundry, they demonstrated that not only do they decompose the acids of the PDK polymers into monomers, but the process also allows the monomers to separate from the entangled additives.

They then showed that the recovered PDK monomers can be transformed into polymers, and those recycled polymers can form new plastic materials without inheriting the color or other characteristics of the original material, so that the broken black belt that was thrown away could find new life . As a computer keyboard if it is made with plastic PDK. They could also recycle the plastic by adding additional features, such as flexibility.

Moving towards a circular plastic future.

Researchers believe that their new recyclable plastic could be a good alternative to many non-recyclable plastics in use today.

"We are at a critical point where we have to think about the infrastructure needed to modernize the recycling facilities for sorting and processing waste in the future," said Helms. "If these facilities were designed to recycle or recycle PDK and related plastics, then we could more effectively divert plastic from landfills and oceans." This is an exciting time to start thinking about how to design materials and recycling facilities to allow Circular plastics, "said Helms.

Next, the researchers plan to develop PDK plastics with a wide range of thermal and mechanical properties for applications as diverse as textiles, 3D printing and foams. In addition, they seek to expand the formulations incorporating materials of plant origin and other sustainable sources.


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