The Near Future Looks Bright for Infinitely Recyclable Plastic

Plastics certainly are a part of practically every product we use every day. The average person in the U.S. generates about 100 kg of plastic waste per year, most of which goes straight to a landfill. A team led by Corinne Scown, Brett Helms, Jay Keasling, and Kristin Persson at Lawrence Berkeley National Laboratory (Berkeley Lab) attempt to change that.

Less than two years ago, Helms announced the invention of a fresh plastic that could tackle the waste crisis at once. Called poly(diketoenamine), or PDK, the material has all the convenient properties of traditional plastics while preventing the environmental pitfalls, because unlike traditional plastics, PDKs can be recycled indefinitely without loss in quality.

Now, the team has released a report that shows what could be accomplished if manufacturers commenced using PDKs on a sizable scale. Underneath line? PDK-based plastic could swiftly become commercially competitive with conventional plastics, and the merchandise will get less costly and more sustainable in the future.

“Plastics were never made to be recycled. The necessity to do so was recognized long afterward,” explained Nemi Vora, first author on the report and a former postdoctoral fellow who worked with senior author Corinne Scown. “But driving sustainability may be the heart of the project. PDKs were made to be recycled from the get-go, and because the beginning, the team has been attempting to refine the production and recycling processes for PDK to ensure that the material could be economical and easy enough to be deployed at commercial scales in anything from packaging to cars.”

The study presents a simulation for a 20,000-metric-ton-per-year facility that generates new PDKs and consumes used PDK waste for recycling. The authors calculated the chemical inputs and technology needed, plus the costs and greenhouse gas emissions, then compared their findings to the same figures for production of conventional plastics.

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

“The questions are how much you will be charged, what the effect on energy use and emissions will be, and ways to get there from where we are today,” added Helms, an employee scientist at Berkeley Lab’s Molecular Foundry. “The next thing of our collaboration is to answer these questions.”

Checking the boxes of cheap and easy
To date, a lot more than 8.3 billion metric a great deal of plastic material have been produced, and almost all this has ended up in landfills or waste incineration plants. A small proportion of plastics are sent to be recycled “mechanically,” meaning they are melted down and then re-shaped into services. However, this technique has limited benefit. Plastic resin itself is made of many identical molecules (called monomers) bound together into long chains (called polymers). Yet to provide plastic its many textures, colors, and capabilities, additives like pigments, heat stabilizers, and flame retardants are put into the resin. When many plastics are melted down together, the polymers become blended with a slew of potentially incompatible additives, resulting in a new material with lower quality than newly produced virgin resin from recycleables. As such, significantly less than 10% of plastic is mechanically recycled more often than once, and recycled plastic usually also contains virgin resin to make up for the dip in quality.

PDK plastics sidestep this issue completely - the resin polymers are engineered to easily break down into individual monomers when blended with an acid. The monomers can then be separated from any additives and gathered to create new plastics without the lack of quality. The team’s earlier research implies that this “chemical recycling” process is light on energy and skin tightening and emissions, and it could 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 seriously beat plastics at their own game, PDKs also have to be convenient. Recycling traditional petroleum-based plastic might be hard, but making new plastic is quite easy.

“We’re discussing materials that are basically not recycled,” said Scown. “So, in conditions of appealing to manufacturers, PDKs aren’t competing with plastic - they must compete with virgin resin. And we were really pleased to observe how cheap and how efficient it'll be to recycle the material.”

Scown, who is a staff scientist in Berkeley Lab’s Energy Technologies and Biosciences Areas, specializes in modeling future environmental and financial impacts of emerging technologies. Scown and her team have been focusing on the PDK project because the outset, helping Helms’ group of chemists and fabrication scientists to select the recycleables, solvents, equipment, and techniques that will lead to the least expensive and eco-friendly product.

“We’re taking early stage technology and designing what it could appear to be at commercial-scale operations” using different inputs and technology, she said. This original, collaborative modeling process allows Berkeley Lab scientists to recognize potential scale-up challenges and make process improvements without costly cycles of trial and error.

The team’s report, published in Science Advances, models a commercial-scale PDK production and recycling pipeline predicated on the plastic’s present state of development. “And the main takeaways were that, once you’ve produced the PDK primarily and you’ve first got it in the system, the price and the greenhouse gas emissions connected with continuing to recycle it back again to monomers and make services could be less than, or at least on par with, many conventional polymers,” said Scown.

Planning to launch
Because of optimization from process modeling, recycled PDKs are already drawing interest from companies needing to source plastic. Always seeking to the near future, Helms and his colleagues have already been conducting market research and meeting with people from industry since the project’s start. Their legwork shows that the very best initial application for PDKs are markets where the manufacturer will receive their product back towards the end of its lifespan, like the automobile industry (through trade-ins and take-backs) and consumer electronics (through e-waste programs). These companies will then be able to reap the advantages of 100% recyclable PDKs in their product: sustainable branding and long-term savings.

“With PDKs, now persons in industry have a choice,” said Helms. “We’re attracting partners who are building circularity into their products and manufacturing capabilities, and providing them with an option that is consistent with future guidelines.”

Added Scown: “We realize there’s interest at that level. Some countries have plans to charge hefty service fees on plastic products that count on non-recycled material. That shift will provide a solid financial incentive to go away from utilizing virgin resins and really should drive a lot of demand for recycled plastics.”

After infiltrating the marketplace for durable products like cars and electronics, the team hopes to expand PDKs into shorter-lived, single-use goods such as packaging.

A full-circle future
As they forge plans for a commercial launch, the scientists are also continuing their techno-economic collaboration on the PDK production process. Although the price tag on recycled PDK has already been projected to be competitively low, the scientists are working on additional refinements to lower the cost of virgin PDK, in order that companies aren't deterred by the original investment price.

And true to create, the scientists are working two steps ahead simultaneously. Scown, who's also vice president for Life-cycle, Economics & Agronomy at the Joint BioEnergy Institute (JBEI), and Helms are collaborating with Jay Keasling, a respected synthetic biologist at Berkeley Lab and UC Berkeley and CEO of JBEI, to create a process for producing PDK polymers using microbe-made precursor ingredients. The procedure currently uses commercial chemicals, but was primarily designed with Keasling’s microbes in mind, thanks to a serendipitous cross-disciplinary seminar.

“Shortly before we started the PDK project, I was in a seminar where Jay was describing all of the molecules that they will make at JBEI with their engineered microbes,” said Helms. “And I got very excited because I saw that some of these molecules were things that we devote PDKs. Jay and I had a few chats, and we realized that nearly the entire polymer could be made using plant material fermented by engineered microbes.”

“Later on, 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 could possibly be more sustainable permanent on the basis of energy, carbon, or water intensity of production and recycling,” Helms continued.

“So, where we are now, this is the first step of many, and I think we have a really long runway in front of us, which is exciting.”

The Molecular Foundry is a Department of Energy (DOE) Office of Science user facility that specializes in nanoscale science. JBEI is a Bioenergy Research Center funded by DOE’s Office of Science.

This work was supported by the DOE’s Bioenergy Technologies Office and Berkeley Lab’s Laboratory Directed Research and Development (LDRD) program.