A New Life for Styrofoam?

Styrofoam, or expanded polystyrene (EPS), has long been used as a packaging material, cushioning products as diverse as laptops, beauty tools, and furniture — and keeping them protected through the rigors of distribution. It has also long been vilified by environmentalists because of the challenges associated with its recyclability.

A new study conducted jointly by researchers from the University of Delaware and Argonne National Laboratory and published in JACS Au, spotlights a fascinating chemical reaction that can convert EPS into PEDOT:PSS, a high-value conducting polymer for electronics. The study demonstrates how upgraded plastic waste can be successfully incorporated into functional electronic devices like silicon-based hybrid solar cells and organic electrochemical transistors.

How the EPS is converted into a valuable resource.

Corresponding author Laure Kayser, assistant professor in the Department of Materials Science and Engineering in UD’s College of Engineering with a joint appointment in the Department of Chemistry and Biochemistry in the College of Arts and Sciences, regularly works with PEDOT:PSS, a polymer that has both electronic and ionic conductivity, and was interested in finding ways to synthesize this material from plastic waste.

According to an article published in University of Delaware’s UDaily, the breakthrough began with a conversation between Kayser and Argonne Chemist David Kaphan about sulfonating polystyrene. Finding a “Goldilocks” reaction fell somewhere between requiring neither caustic reagents for higher conversion efficiencies or milder materials that yielded a less efficient results. After months of trial and error, the research team landed on a solution that successfully subjected EPS to a high polymer sulfonation with minimal defects and high efficiency, all while using a mild sulfonating agent. Their method also resulted in an efficient way to convert plastic waste into PEDOT:PSS.

Not only were the researchers able to find reaction conditions that resulted in high polymer sulfonation, minimal defects, and high efficiency with a mild sulfonating agent, this new method is also an efficient way to convert plastic waste into PEDOT:PSS. Photo by Evan Krape/UD.

Once the researchers had PEDOT:PSS in hand, they were able to compare how their waste-derived polymer performed compared to commercially available PEDOT:PSS. “In this paper, we looked at two devices — an organic electronic transistor and a solar cell,” said Chun-Yuan Lo, a chemistry doctoral candidate and the paper’s first author. “The performance of both types of conductive polymers was comparable, and shows that our method is a very eco-friendly approach for converting polystyrene waste into high-value electronic materials.”

One of the chemistry-related findings the researchers discovered was the ability to use stoichiometric ratios during the reaction. “Being able to use a stoichiometric ratio means that we can minimize the amount of waste being generated,” Kelsey Koutsoukos, a materials science doctoral candidate and second author of this paper, told UDaily. 

This is a finding that the Kayser group will delve deeper into as they “fine tune” the sulfonation process, according to the UDaily article. “Along with studying how this degree of sulfonation impacts the electrical properties of PEDOT:PSS, the team is interested in seeing how this fine-tuning capability can be used for other applications, such as fuel cells or water filtration devices, where the degree of sulfonation greatly impacts a material’s properties,” the article reports.

In addition to contributing to packaging waste sustainability efforts, the research has another takeaway. “For the electronic devices community, the key takeaway is that you can make electronic materials from trash, and they perform just as well as what you would purchase commercially,” Kayser says. “For the more traditional polymer scientists, the fact that you can very efficiently and precisely control the degree of sulfonation is going to be of interest to a lot of different communities and applications.”

What could the impact be on EPS foam used in packaging?

Packaging Digest spoke to Kayser and asked if it might be possible to make this PEDOT:PSS material if the foam has been compacted, given that EPS is often compressed before being recycled to minimize the volume during transportation to a recycling facility. She replies that although the team hasn’t explored that angle, “the first step to our process is to dissolve EPS in an organic solvent, so I am quite sure that it would not make a difference compacted or not.”

As for the impact this discovery has on the sustainability profile of EPS used in packaging, Kayser says a full life cycle analysis would be warranted. “One concern of EPS remains the scale at which it is generated: the demand for PEDOT:PSS would probably not match that scale,” she says. “But, making PEDOT:PSS from plastic waste rather than producing new plastics for that specific purpose could be very powerful! And, that is just one example of a specialty material could be made from EPS waste through plastic upgrading.”

Betsy Bowers, executive director of EPS Industry Alliance (EPS-IA), and Jon Timbers, chief sustainability officer of Epsilyte, a member of EPS-IA, are excited by the potential promise of this study.

“The successful conversion of waste EPS into a high-value conducting polymer marks a significant advancement in sustainability and highlights the potential of upcycling plastic waste,” Bowers says. “This research showcases the versatility of recycled EPS for innovative uses, demonstrating how this material can contribute to environmental stewardship and a circular economy, while driving technological innovation.”

Timbers agrees, adding that the creation of a circular economy for polystyrene relies on discovering high value second uses for discarded plastics. “This research is an example of a newly discovered high value second use for discarded foam, and that is exciting,” he says. “As the recycling infrastructure for foam grows, we are excited about this research uncovering additional ways to turn old polystyrene into something valuable again.”