Scientists from the United States have discovered a chemical reaction that can transform waste plastic, namely polystyrene foam, into the valuable conductive polymer PEDOT:PSS. This polymer has shown comparable performance to commercially available analogues when used in organic electronic transistors and solar cells.
Image Source: National Cancer Institute/Unsplash
Researchers at the University of Delaware and Argonne National Laboratory have developed a method for synthesizing PEDOT:PSS by sulfonating polystyrene, a synthetic plastic widely used in single-use containers and packaging materials. According to EurekAlert, the study, published in the journal JACS Au, demonstrates the successful incorporation of recycled plastic waste into ultimately functional electronic devices, including hybrid silicon solar cells and organic electrochemical transistors (OETs).
Sulfonation is a common chemical reaction in which a hydrogen atom is replaced by a sulfonic acid. This process is part of the technology for the production of dyes, drugs and ion exchange resins (ion exchangers), which are synthetic polymers. Chemical reactions can be either “hard” (with higher final efficiency, but requiring caustic reagents) or “soft” (less efficient, but using milder reagents). The scientists wanted to find something in between: “We needed a reagent that was efficient enough to achieve a really high degree of functionalization, but would not spoil the polymer chain,” explains study leader Laura Kayser.
Image source: Evan Krape/University of Delaware
However, the key achievement was the development of a “soft” sulfonation method, which provided a high degree of functionalization of the polymer without destroying its chain. Dr. Kelsey Koutsoukos noted that the team conducted months of experiments to find the optimal reaction conditions.
«We tested different organic solvents, different molar ratios of the sulfonating agent, and evaluated different temperatures and times to see what conditions were best to achieve a high degree of sulfonation,” he said.
Ultimately, it was possible to find reaction conditions that resulted in high sulfonation of the polymer, minimal defects and high efficiency, all while using a mild sulfonating agent. The ability to precisely control the extent of the entire process was also discovered, which opens up prospects for applications in various fields, including fuel cells and water filtration devices.
The researchers emphasize that their work could significantly contribute to global sustainability efforts by offering a new way to recycle waste into valuable materials. One of the main authors of the work, graduate student Chun-Yuan Lo, noted: “Many scientists are working on the problem of recycling and recycling used raw materials, and our study is another example of how this problem can be solved.” The waste-derived polymer was compared with commercially available PEDOT:PSS. The performance of both types was identical.