A breakthrough method of transforming plastic waste into functional electronic devices

Scientists from the University of Delaware and Argonne National Laboratory have developed a chemical reaction that transforms Styrofoam into a high-performance conductive polymer known as PEDOT:PSS.

This breakthrough discovery, detailed in a new paper published in the journal JACS Au, shows how improved plastic waste can be incorporated into functional electronic devices such as silicon-based hybrid solar cells and organic electrochemical transistors.

Laure Kayser, assistant professor at the University of Delaware, and her team work with PEDOT:PSSpolymer known for its electronic and ionic conductivity. They decided to synthesize this material from plastic waste.

The research collaboration began when Kayser connected with Argonne chemist David Kaphan at a UD event. The teams hypothesized that PEDOT:PSS

can be obtained by sulfonating polystyrene, a synthetic plastic used in disposable containers and packaging materials.

Sulfonation, a process that involves replacing a hydrogen atom with a sulfonic acid, can create a variety of products, including dyes, drugs, and ion-exchange resins. The researchers wanted to find a middle ground between “hard” and “soft” sulfonation methods. “A reagent that is efficient enough to get really high degrees of functionalization, but that doesn’t disrupt the polymer chain,” Kayser explained.

Initially, the researchers used the method described in a previous study to sulfonate small molecules using 1,3-disulfonic acid imidazolium chloride ((Dsim)Cl). However, adding functional groups to the polymer is more difficult due to difficulties in separating the byproducts and maintaining the properties of the polymer chain.

After months of trial and error, the researchers optimized the conditions to minimize side reactions. “We explored different organic solvents, molar ratios of sulfonating agent, and evaluated different temperatures and times,” said Kelsey Koutsoukos, a materials science doctoral student and co-author.

They found conditions that resulted in high polymer sulfonation, minimal defects, and high yields using a mild sulfonating agent. Using waste polystyrene as a starting material, their method effectively converted waste plastic into PEDOT:PSS

Comparison of their waste-derived polymer with commercially available polymers PEDOT:PSS

tested it in two devices: an organic electronic transistor and a solar cell. “The performance was comparable, showing that our method is environmentally friendly for converting polystyrene waste into high-value electronic materials,” said Chun-Yuan Lo, a doctoral student in chemistry and lead author.

Detailed analyses at UD included X-ray photoelectron spectroscopy, film thickness analysis, and solar cell evaluation. Advanced Argonne spectroscopic equipment, such as carbon NMR, was used for detailed polymer characterization.

An unexpected discovery was the possibility of using stoichiometric ratios during the reaction. “Usually, polystyrene sulfonation involves using an excess of aggressive reagents. Here, we minimized waste by using a stoichiometric ratio,” Koutsoukos noted.

The discovery will help Kayser’s group “fine-tune” the degree of sulfonation, which will affect the electrical properties PEDOT:PSS.

“The big thing for the electronics community is that you can make electronic materials from junk that work just as well as commercially available materials,” Kayser said. “For traditional polymer scientists, efficient and precise control of sulfonation will appeal to a variety of communities and applications.”

The researchers believe their work could significantly contribute to global sustainability efforts by transforming waste into value-added materials. “Our study provides another example of how upcycling and recycling can solve problems,” Lo said.