Researchers transform Styrofoam into high-value conducting polymer

Photo Credit: Adobe Stock/aulia sailan ilma

Researchers from the University of Delaware (UD) and Argonne National Laboratory, in Lemont, Ill., claim to have discovered a chemical reaction that can convert Styrofoam into a high-value conducting polymer known as PEDOT:PSS.

The process involves turning polystyrene, the main component of Styrofoam, into a sulfonate. This approach allows the repurposing of plastic waste into functional electronic materials for devices like silicon-based hybrid solar cells and organic electrochemical transistors.

After connecting with Argonne chemist David Kaphan during an event hosted by UD’s research office, the research teams at UD and Argonne began evaluating the hypothesis that PEDOT:PSS could be made by sulfonating polystyrene. Sulfonation is a common chemical reaction where a hydrogen atom is replaced by sulfonic acid, and the process is used to create a variety of products such as dyes, drugs and ion exchange resins. These reactions can either be “hard“ (with higher conversion efficiency but that require caustic reagents) or “soft” (a less efficient method but one that uses milder materials).

The researchers first turned to a method described in a previous study for sulfonating small molecules. This study showed promising results in terms of efficiency and yield, using 1,3-Disulfonic acid imidazolium chloride ([Dsim]Cl). But adding functional groups onto a polymer is more challenging than for a small molecule, the researchers explained, because not only are unwanted byproducts harder to separate, but any small errors in the polymer chain can also change its overall properties.

To address this challenge, the UD and Argonne researchers embarked on many months of trial and error to find the optimal conditions that minimized side reactions. “We screened different organic solvents, different molar ratios of the sulfonating agent, and evaluated different temperatures and times to see which conditions were the best for achieving high degrees of sulfonation,” said Kelsey Koutsoukos, a materials science doctoral candidate at UD.

The researchers were able to find reaction conditions that resulted in high polymer sulfonation, minimal defects and high efficiency, all while using a mild sulfonating agent. And because the researchers were able to use polystyrene, specifically waste Styrofoam, as a starting material, their method also represents an efficient way to convert plastic waste into PEDOT:PSS.

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. Specific analyses conducted at UD included X-ray photoelectron spectroscopy (XPS) at the surface analysis facility, film thickness analysis at the UD Nanofabrication Facility, and solar cell evaluation at the Institute of Energy Conversion. Argonne’s advanced spectroscopy equipment, such as carbon NMR, was used for detailed polymer characterization. Additional support was provided by materials science and engineering professor Robert Opila for solar cell analysis and by David C. Martin, the Karl W. and Renate Böer Chaired Professor of Materials Science and Engineering, for the electronic device performance analyses.

For the electronic devices community, the researchers said, the key takeaway is that you can make electronic materials from trash, and they perform just as well as what you would purchase commercially. “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,” said Laure Kayser, assistant professor in the Department of Materials Science and Engineering in UD’s College of Engineering.

The researchers also see great potential for how this research can contribute to ongoing global sustainability efforts by providing a new way to convert waste products into value-added materials.