Mechanochemical Degradation and Fluoride Recovery of Perfluorosulfonic Acid Polymer Membrane

Per- or polyfluoroalkyl substances (PFAS) represent a large family of chemicals, widely used due to their outstanding properties. However, also known as "Forever Chemicals", they are raising attention due to high health and environmental risks. In last years, the elimination, degradation, or recycling of PFAS has become essential. In this work, the degradation of a perfluorosulfonic acid polymer, Nafion, composed of a poly(tetrafluoroethylene) backbone with perfluoroether side chains terminated by sulfonic acid groups, is studied. More precisely, the mechanochemical degradation, previously described for linear fluoropolymers, is reported on branched PFSA polymers in the presence of various activators (such as (pyro)phosphates, 1,8-Diazabicyclo [5.4.0]undec-7-ene (DBU), 1,5,7-Triazabicyclo [4.4.0]dec-5-ene(TBD), KOH) at room temperature. Recovered products were characterized over time by nuclear magnetic resonance and Fourier transformation infrared spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and liquid chromatography-mass spectrometry in order to both identify the released products and suggest a degradation pathway. The use of potassium hydroxide, although resulting in a moderate potassium fluoride yield, allowed the determination of fragments produced during the degradation mechanism, while others were ineffective. Phosphate salts have been revealed to be the best candidates enabling the mineralization of PFSA, yielding valuable products and a good fluorine recovery for a further circular economy.