Materials

New recyclable plastic can break its molecular bonds and start over

Berkeley Lab researchers have developed a new type of plastic (not pictured) that can be broken down to its molecular components and recycled
Berkeley Lab researchers have developed a new type of plastic (not pictured) that can be broken down to its molecular components and recycled
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A piece of PDK plastic sitting in acid, which breaks the molecular bonds of the material and allows it to be reused
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A piece of PDK plastic sitting in acid, which breaks the molecular bonds of the material and allows it to be reused
Researchers Peter Christensen, Kathryn Loeffler, and Brett Helms
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Researchers Peter Christensen, Kathryn Loeffler, and Brett Helms
The idea of recyclable plastics like PDK is to make the industry more circular
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The idea of recyclable plastics like PDK is to make the industry more circular
Unlike existing plastics, PDK can be broken down and separated from other chemical additives, allowing its monomers to be reused
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Unlike existing plastics, PDK can be broken down and separated from other chemical additives, allowing its monomers to be reused
Berkeley Lab researchers have developed a new type of plastic (not pictured) that can be broken down to its molecular components and recycled
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Berkeley Lab researchers have developed a new type of plastic (not pictured) that can be broken down to its molecular components and recycled

Plastics are useful and ubiquitous – but that's not always a good combination. The vast majority of plastic waste can't be recycled, meaning it ends up in landfills at best or the ocean at worst. To help curb the problem, researchers at Berkeley Lab have now designed a new type of plastic that can apparently be reduced right back to its molecular parts, before being remade over and over.

According to the United Nations, about 300 million tonnes of plastic waste is produced every year. It's not surprising then that this garbage has found its way to the deepest parts of the oceans, is moving up the food chain and may even leave an indelible imprint on the Earth's geological record.

With awareness of the issue increasing, we're seeing bans on single-use plastics, huge ocean cleanup projects setting sail, and creative uses for recovered plastic waste, such as turning them into things as varied as bike paths, shoes, art installations and diesel fuel.

Even with all those options on the table, the majority of plastic waste ends up in landfills or incinerators, and that's largely because plastic is a tricky material to recycle. The problem is that different types of plastics – whether they're hard or soft, brightly colored or clear – are usually recycled together. That means they all get mashed up into one new substance with some relatively unpredictable properties.

Unlike existing plastics, PDK can be broken down and separated from other chemical additives, allowing its monomers to be reused
Unlike existing plastics, PDK can be broken down and separated from other chemical additives, allowing its monomers to be reused

So rather than design a plastic based on its life in use, the Berkeley Lab team focused on its afterlife. The new creation, named poly(diketoenamine) or PDK, can be reduced back to its constituent molecular parts and then reassembled as needed.

"Most plastics were never made to be recycled," says Peter Christensen, lead author of the study. "But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective."

The most basic building blocks of plastics are molecules called monomers, which are tightly bound together into polymers and mixed with other chemical additives. Normally those bonds are hard to break, but the monomers in PDK plastic are designed to come apart more easily, allowing them to later be rebuilt into something new.

"With PDKs, the immutable bonds of conventional plastics are replaced with reversible bonds that allow the plastic to be recycled more effectively," says Brett Helms, lead researcher on the study.

A piece of PDK plastic sitting in acid, which breaks the molecular bonds of the material and allows it to be reused
A piece of PDK plastic sitting in acid, which breaks the molecular bonds of the material and allows it to be reused

To do so, an old piece of PDK plastic can be dunked into acid. That degrades those bonds and reduces the material back to its original monomers, as well as separating them from other chemical additives. These monomers can then be reused in new plastic products.

The team tested various mixtures of the material, and then demonstrated that the whole cycle can work as hoped. The PDK plastics were effectively broken down in acid, and the resulting monomers were then rebuilt into new plastics. The colors and other properties of the old products didn't affect the new ones. The team says the plastics could also be "upcycled" into higher quality products by adding new chemicals.

Acid isn't the only way to break it down though. Other recyclable plastics can apparently revert back to their monomer state using heat, or other chemical catalysts.

The ultimate goal of PDKs and other recyclable plastics is to make the plastic industry more "circular," instead of linear that leads to the sea. But of course, that would require some pretty large infrastructure changes, including new collection programs and specialized facilities.

"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," says 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."

The research was published in the journal Nature Chemistry.

Source: Lawrence Berkeley National Laboratory

4 comments
Roomie
How would this new plastic mitigate the following statement from the article: "The problem is that different types of plastics – whether they're hard or soft, brightly colored or clear – are usually recycled together. That means they all get mashed up into one new substance with some relatively unpredictable properties." If it's not sorted separately how will you be able to recycle it? I think any new "plastic" needs to be compostable where it will need to be degradable by itself and not harmfull for the environment. Anything needing human interaction to recycle will just have the same inherent problems as we see today.
Nik
Roomie. Absolutely!
OwkayeGo
I think all plastic bottled drinks, when sold at retail, should be charged a refundable $1 "recycling deposit". Buy a case of 12 drinks in plastic bottles and pay an extra $12 at the register. Then get that $12 deposit back when you recycle those bottles later ... or just "suck it up" and lose the $12 recycling deposit because you do not return them for a refund. I'm not sure if they still do this in some parts of the country, but in upstate New York where I grew up they used to do this for glass bottles, although not at the same $1 per bottle rate. Instead I think it was only 25 cents per bottle, or maybe even less. Fortunately it made everyone aware of how much glass they were previously just tossing in the trash. And kids wanted to collect bottles for the refunds! I don't see why something similar couldn't be done for plastic bottles, but in order for it to work today it would be necessary to make the per-bottle deposit substantial enough that 99% of people would absolutely recycle their empty bottles -- so make it $5 per bottle if $1 isn't enough. There's always a way to solve serious problems, but these days too many people have become wimps who whine about the problems -- and potential solutions that would actually work -- rather than actively supporting those solutions.
owlbeyou
This finding at Berkley Labs is definitely in the right direction, and it's about time! Plastic is an incredibly useful material and we have to use it responsibly. There is a relatively new trend in packaging of foods with the use of compostable 'plastics' that break down far quicker. This is a classic "let's treat the symptom and not the disease" all over again. This biodegradable packaging complicates the recycling process by the very fact that if it mistakenly ends up in the recycling process, it will contaminate other plastic rendering the batch useless. Silly people. It's just another marketing ploy to extract money from your piggy bank.