Infinitely Recyclable Plastic – PDK poly(diketoenamine)

“Plastics are a part of nearly every product we use on a daily basis. The average person in the U.S. generates about 100 kg of plastic waste per year, most of which goes straight to a landfill.

Less than two years ago, Helms announced the invention of a new plastic that could tackle the waste crisis head on. Called poly(diketoenamine), or PDK, the material has all the convenient properties of traditional plastics while avoiding the environmental pitfalls, because unlike traditional plastics, PDKs can be recycled indefinitely with no loss in quality.

Now, the team has released a study that shows what can be accomplished if manufacturers began using PDKs on a large scale. PDK-based plastic could quickly become commercially competitive with conventional plastics, and the products will get less expensive and more sustainable as time goes on.

 “But driving sustainability is the heart of this project. PDKs were designed to be recycled from the get-go, and since the beginning, the team has been working to refine the production and recycling processes for PDK so that the material could be inexpensive and easy enough to be deployed at commercial scales in anything from packaging to cars.”

“These days, there is a huge push for adopting circular economy practices in the industry. Everyone is trying to recycle whatever they’re putting out in the market,” said Vora. “We started talking to industry about deploying 100% infinitely recycled plastics and have received a lot of interest.”

“The questions are how much it will cost, what the impact on energy use and emissions will be, and how to get there from where we are today,” added Helms.

When many plastics are melted down together, the polymers become mixed with a slew of potentially incompatible additives, resulting in a new material with much lower quality than newly produced virgin resin from raw materials. As such, less than 10% of plastic is mechanically recycled more than once, and recycled plastic usually also contains virgin resin to make up for the dip in quality.

PDK plastics sidestep this problem entirely

1. The resin polymers are engineered to easily break down into individual monomers when mixed with an acid
2. The monomers can then be separated from any additives and gathered to make new plastics without any loss of quality

The team’s earlier research shows that this “chemical recycling” process is light on energy and carbon dioxide emissions, and it can be repeated indefinitely, creating a completely circular material lifecycle where there is currently a one-way ticket to waste. Yet despite these incredible properties, to truly beat plastics at their own game, PDKs also need to be convenient. Recycling traditional petroleum-based plastic might be hard, but making new plastic is very easy.

“And the main takeaways were that, once you’ve produced the PDK initially and you’ve got it in the system, the cost and the greenhouse gas emissions associated with continuing to recycle it back to monomers and make new products could be lower than, or at least on par with, many conventional polymers,” said Scown.

A full-circle future

Plans are in place to design a process for producing PDK polymers using microbe-made precursor ingredients.

“In the future, we’re going to bring in that biological component, meaning that we can begin to understand the impacts of transitioning from conventional feedstocks to unique and possibly advantaged bio-based feedstocks that might be more sustainable long term on the basis of energy, carbon, or water intensity of production and recycling,” Helms continued.

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