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Breakthrough discovery: New plastic can be fully recycled again and again

11 May 2019

In traditional plastic recycling, additives can not be separated from monomers.

Every day, millions of us drop a plastic bottle or cardboard container into the recycling bin - and we feel we're doing our bit for the environment.

But now researchers at the Lawrence Berkeley National Lab have reported that they've developed a type of plastic, called PDK, that can be recycled over and over again, thus solving the problem of plastics that cannot be easily recycled.

But a new research effort led by scientists at Berkeley Lab could provide a solution in the form of plastics that are designed from the ground up to be fully recyclable.

"Circular plastics and plastics upcycling are grand challenges", says Brett Helms, a staff scientist at Berkeley's Molecular Foundry.

Plastics today are made up of large molecules called polymers which in turn are created from shorter compounds called monomers.

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This means that instead of a container becoming another new container, it becomes a different, less useful product instead of completing the "recycling loop".

The end result is a plastic ingredient that can shake off any colours or strengthening agents in several easy steps to be turned back into another product.

Next, they demonstrated that the recuperated PDK monomers can be changed into polymers, and those reused polymers can shape new plastic materials without acquiring the shading or different highlights of the first material - so broken dark watchband you hurled in the garbage could discover new life as a PC console if it's made with PDK plastic. The goal is to improve the recycling process so that fewer plastics end up in landfills or oceans.

There are many hurdles that make recycling plastics hard.

The full study was published last month in the journal Nature Chemistry.

Condensing these units into a long string forms a plastic called poly (diketoenamine) - or PDK - and the bonds can be dissolved easily using nothing more than a 12-hour soak in a strong acid bath.

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This is where PDK plastic comes in.

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.

"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", Helms added, advocating for the modernization of recycling facilities.

"With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively."
Unfortunately, these chemicals remain tightly bound to the monomers of the plastics even after they have gone through the recycling process. They could also upcycle the plastic by adding additional features, such as flexibility. "This is an exciting time to start thinking about how to design both materials and recycling facilities to enable circular plastics", said Helms.

Moving forward, the team plans to develop PDK plastics with a range of thermal and mechanical properties, as well as plant-based materials and other sustainable sources. Right now, the team is working on making the material greener by incorporating plant-based materials.

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Breakthrough discovery: New plastic can be fully recycled again and again