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

Depolymerized Plastics

Source Peter Christensen | Brett Evans | Angelique Scheuermann | Kathryn Loeffler Berkeley Lab

In a new study published in Nature Chemistry, researchers reported that the monomers of the new material, known as poly (diketoenamine) or PDK, could be recovered free from compounded additives using a simple acid bath.

Researchers at the US Department of Energy's Lawrence Berkeley National Laboratory have developed a new kind of plastic that they say will allow for endless recycling of plastic that often ends up in a landfill or worse.

All plastics are made up of different monomers that bond with different chemicals to take on unique properties, such as additives that strengthen the plastic to make it tough and sturdy or others that make the plastic more pliable and stretchy.

"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", said study researcher Brett Helms, from Berkeley Lab's Molecular Foundry.

In a flawless world, plastic would never be on a one-way trip into landfill - it's a vision we've strived to realise for decades.

As it turns out, plastics that should be recycled can't be because of certain chemical qualities that the material has taken on because of additives, reducing the effectiveness of global recycling efforts.

But a team of researchers at Berkeley Lab might just have changed that - with a find described as the'Holy Grail', a plastic which can be recycled into dozens of different materials, again and again.

"We're interested in the chemistry that redirects plastic lifecycles from linear to circular", said Helms.

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. That includes adhesives, phone cases, watch bands, shoes, computer cables, and hard thermosets that are created by molding hot plastic material.

After testing various formulations at the Molecular Foundry, they demonstrated that not only does acid break down PDK polymers into monomers, but the process also allows the monomers to be separated from entwined additives. "This is an exciting time to start thinking about how to design both materials and recycling facilities to enable circular plastics". The most recyclable form of plastic, polyethylene terephthalate, is only recycled at a rate between 20 to 30 percent, with the rest going into landfills or incinerators.

The researchers believe that their new recyclable plastic could be a good alternative to many nonrecyclable plastics in use today. Right now, the team is working on making the material greener by incorporating plant-based materials.

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