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Polytetrafluoroethylene (PTFE) is a synthetic fluorine-based polymer with a wide range of applications, including non-stick cookware production and electrical and optical fiber cable coating, owing to its high durability, thermal stability, and low friction. Ironically, its durability also presents an environmental challenge for its disposal. PTFE is mainly disposed of via incineration, landfilling, and defluorination. However, incineration requires high energy and involves the release of hydrogen fluoride, which is highly corrosive.

Meanwhile, landfilling leads to an environmental burden of undegraded PTFE. By contrast, defluorination, in which PTFE is converted into its constituent fluorine compounds, is eco-friendly, as it enables polymer recycling. Unfortunately, traditional PTFE defluorination either requires high-temperature reactions (>500 °C) or complex reagents for the more manageable low-temperature reactions (<100 °C). Moreover, in either case, the efficiency of fluorine recovery has not been explored.

To address this gap and improve fluorine recovery via PTFE defluorination, a group of international researchers led by Professor Norio Shibata from Nagoya Institute of Technology (NITech) in Japan has recently developed a novel defluorination method that utilizes sodium dispersion to degrade PTFE and recover fluoride ion under mild conditions. Their study also involved the contributions of Mr. Taichi Araki and Mr. Hibiki Ota from NITech.

The work is in Nature Communications.

In the new method, a remarkable fluoride ion yield (in the form of sodium fluoride) of up to 98% was achieved from PTFE using sodium dispersion (two equivalents) in tetrahydrofuran (THF) at a reaction temperature of 25° C and a reaction duration of 12 hours.

The major advantage of this defluorination approach is that it can operate at room temperature, avoiding the need for extreme conditions. To further verify fluoride recovery, the team examined the elements in the black residue obtained after PTFE degradation under optimized conditions using spectral analysis and estimated that the proportion of fluoride lost from PTFE was 93.5%.

Further analysis of this residue using X-ray diffraction, Raman and infrared spectroscopy, and nuclear magnetic resonance confirmed efficient fluoride recovery from PTFE. In addition, morphological analysis using scanning electron microscopy with energy-dispersive X-ray spectroscopy revealed that the defluorination process transformed PTFE's morphology, from an initial dense, irregularly shaped grainy texture with smooth surfaces into a black residue with a highly irregular rough surface showing cracks.

Furthermore, the team examined the applicability of this method for other fluorine-based compounds and found that it could efficiently recover fluorine (up to 97%) from per- and polyfluoroalkyl substances (PFAS) as well, namely perfluorononanoic acid, perfluorooctanoic acid, perfluorobutanesulfonic acid, and trifluoroacetic acid, once the reaction duration and sodium dispersion quantity were properly fine-tuned.

Prof. Shibata notes, "In addition to PTFE, other fluorine-containing compounds are major environmental pollutants. Our defluorination method could effectively degrade PFAS, indicating its broad applicability."

As already noted, PTFE and PFAS, despite their utility, pose a major environmental concern in relation to their effective degradation. Developing an effective and robust defluorination method could not only help mitigate such environmental hazards but also enhance the recovery and circulation of fluorine as a valuable resource.

"In contrast to the conventional PFAS defluorination methods that require plasma processing or incineration at elevated temperatures, our defluorination method is an eco-friendly, non-energy-intensive approach with reduced toxic gas emissions that not only improves fluorine resource utilization but can help minimize our dependence on fluorite in the future," concludes Prof. Shibata.