A multidisciplinary Berkeley Lab team has been working for several years to develop a game-changing plastic that, unlike traditional plastics, can be recycled indefinitely and is not made from petroleum. Their latest milestone was the release of an analysis showing the feasibility and potential outcomes of launching the unique material, called poly(diketoenamine) or PDK, into the market at an industrial scale.
The team found that making products out of recycled PDK could quickly become as cheap as making the same item with new plastic polymers (a very small proportion of our current plastics are recycled, so most products are made from “virgin” plastic resin), while also reducing CO2 emissions and energy requirements of manufacturing. Furthermore, the scientists plan to develop a process to create the initial PDK resin using microbe-fermented plant material, meaning that the entire lifecycle of a PDK plastic product could be low-carbon or even carbon neutral.
Once the infrastructure for large-scale PDK production and recycling is developed, the scientists envision that PDK could replace traditional plastics in a variety of consumer products, from car parts to water bottles.
We spoke with two project leaders, Brett Helms and Corinne Scown, about the inspiration for PDK, shortfalls in our current recycling systems, and how this ambitious project is enabled by a diverse combination of scientific expertise.
Brett Helms is a chemist and fabrication scientist working at Berkeley Lab’s Molecular Foundry, a U.S. Department of Energy (DOE) user facility. Helms led the group that invented PDK more than three years ago, as part of a Laboratory Directed Research and Development (LDRD) Program project focused on creating a highly functional plastic alternative.
Corinne Scown is a scientist in Berkeley Lab’s Energy Technologies Area, and Vice President for the Life-cycle, Economics, and Agronomy Division at the Joint BioEnergy Institute (JBEI) – a DOE Bioenergy Research Center. Scown, an expert in the field of technoeconomic analysis, leads the design and development of processes for industrial-scale PDK production and recycling. By modeling how these systems would work on a large scale, her work identifies potential bottlenecks and predicts both cost and environmental impact, thereby helping materials scientists select the most efficient and sustainable technologies from an early stage.
Q. Brett, where did the idea or inspiration for PDK come from?
Brett: The way industry practices polymer recycling is changing. Currently, the approach relies on mechanical recycling where, after sorting and grinding, polymer waste is melted into a homogenized material whose characteristics have degraded along the way. In the future, chemical recycling is expected to play a bigger role, as it prioritizes recovery of high-value materials that can be reused in manufacturing. However, with current chemical recycling technology, very few polymers can be efficiently recycled, whether we measure efficiency on the basis of the energy required, the amount of CO2 emitted, or the amount of pristine material we recover for secondary resin manufacturing. We were aware of these challenges and approached the problem from that perspective. We tried to design PDKs as next-generation polymers that require only small amounts of energy to be chemically recycled back to their original monomers with high yields, such that carbon in PDKs can be recirculated across limitless cycles of remake-and-reuse.
Q. Corinne, what drew you to this work?
Corinne: I’ve done work on technoeconomic analysis and life-cycle assessment of biofuels for years now and, believe it or not, plastics are not a huge leap. We’ve been exploring bio-based products for some time now, and biopolymers were already interesting to us because we know that it’s crucial to find renewable alternatives for all the different products we make from the typical barrel of oil, not just fuels. Brett and Jay pulled me in when they were writing the proposal for this particular project and I was floored by the clarity of vision and how quickly it all came together. The idea of a polymer that can be recycled back to virgin-quality monomers with minimal energy input solves a lot of otherwise intractable problems with plastic waste.
Q. Brett, how did you get into materials science? Was there always a goal to create environmentally conscious materials, or did you start out with another goal?
Brett: I did undergraduate research with Shenda Baker at Harvey Mudd College, where we were studying the physics of polymers at interfaces. At some point, I realized that if I wanted to study interesting polymers, I might need to learn how to make them myself. Shenda introduced me to Craig Hawker, and I spent time learning polymer synthesis from him and Eva Harth at the IBM Almaden Research Center. Feeling more confident in my synthesis abilities, I then became interested in learning how to design function into polymers. That’s what led me to UC Berkeley, where I conducted my Ph.D. with Jean Fréchet, whose group was well known for its creativity in functional polymers. I also learned, in my postdoc with Bert Meijer, at the Eindhoven University of Technology in the Netherlands, how interactions between polymers and other materials are central to their function.
Working at a National Lab has really opened my eyes to the breadth in which materials make a difference in our lives, and increasingly in the sustainability of our life-choices. I hope that, in our work with rethinking polymer chemistry for the circular economy, we offer creative solutions that everyone can get excited by and learn from, and that people might be motivated to work with us to bring those solutions to the world, in line with our mission here at Berkeley Lab.
Q. Corinne, the term “technoeconomic analysis” is probably new for a lot of people. How do you explain what you do when a non-scientist asks?
Corinne: Technoeconomic analysis, or TEA for short, is one of those terms that didn’t get used much a decade ago and it’s a lot more common now. At a basic level, TEA involves engineering design and cash flow analysis. The engineering design and simulation is usually the hard part. You’re taking a cool result someone got in the lab and trying to figure out what a commercial-scale facility would look like, including everything from solvent recovery to heat and power generation to waste handling. This usually involves thinking through things that the scientists haven’t considered and it can raise interesting questions. For example, TEA showed that one of the reactants in the discovery-based chemistry for synthesizing virgin PDK – N,N’-dicyclohexylcarbodiimide (DCC) – proved to be pretty expensive, emissions-intensive, and it resulted in the generation of hazardous waste from the process. You could say that DCC had a target on its back after that – Brett’s team was set on finding a way to reduce or eliminate its use.
Q. A lot of people get confused about plastic recycling. For example, what’s recyclable versus what isn’t? What happens to it after you put it in…