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. A team at Lawrence Berkeley National Laboratory set out to change that. Less than two years ago, they announced the invention of a new plastic that could tackle the waste crisis head-on. It’s called polydiketoenamine, 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.
According to a study recently published in the journal Science Advances 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. Most important, 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.
The new study presents a simulation for a 20,000-metric-ton-per-year facility that puts out new PDKs and takes in used PDK waste for recycling. The authors calculated the chemical inputs and technology needed, as well as the costs and greenhouse gas emissions, then compared their findings to the equivalent figures for production of conventional plastics. To date, more than 8.3 billion metric tons of plastic material have been produced, and the vast majority of it 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 reshaped into new products. However, this technique has limited benefits. The plastic resin itself is made of many identical molecules (called monomers) bound together into long chains (called polymers). Yet to give plastic its many textures, colors, and capabilities, additives like pigments, heat stabilizers, and flame retardants are added to the resin.
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 — the resin polymers are engineered to easily break down into individual monomers when mixed with an acid.
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. In terms of appealing to manufacturers, PDKs aren’t competing with recycled plastic — they have to compete with virgin resin. And the team was really pleased to see how cheap and how efficient it will be to recycle the material.
The team’s new report, published in Science Advances, models a commercial-scale PDK production and recycling pipeline based on the plastic’s current state of development. 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 many conventional polymers. Thanks to optimization from process modeling, recycled PDKs are already drawing interest from companies needing to source plastic.
The team has been conducting market research and meeting with people from the plastics industry since the project’s early days. And their legwork shows that the best initial application for PDKs are markets where the manufacturer will receive their product back at the end of its lifespans, such as the automobile industry (through trade-ins and takebacks) and consumer electronics (through e-waste programs). These companies will then be able to reap the benefits of 100% recyclable PDKs in their product including sustainability-based branding and long-term cost savings. After infiltrating the market for durable products like cars and electronics, the team hopes to expand PDKs into shorter-lived, single-use goods such as packaging. Meanwhile, the scientists are also continuing their techno-economic collaboration on the PDK production process.
Although the cost of recycled PDK is already projected to be competitively low, the scientists are working on additional refinements to lower the cost of virgin PDK, so that companies are not deterred by the initial investment price. One possibility is to design a process for producing PDK polymers using microbe-made precursor ingredients. The process currently uses industrial chemicals but was initially designed with special microbes in mind. In the future, the team plans to bring in that biological component. Importantly, PDK technology is already available to interested companies for licensing and collaboration.