Mixing enthalpies of fluorinated precursors for textile industry in ionic liquids

Per- and polyfluoroalkyl substances (PFAS) are widely used for technical purposes in textile finishing, giving water or oil repellence to the fibres. During their production, textile manufacturing or consumer-use, these additives can be degraded into their precursors and released in the environment. These substances are volatile, bio accumulative and persistent, and their release in the environment is more and more regulated in the EU . For a textile recycling purpose, it is necessary to find ways to safely remove them from the fibres. Among other alternative solvents, ionic liquids showed solvation properties that are promising for recycling textile waste. We have used the COSMO-SAC modelling approach to screen a large number of ionic liquids and, by the calculation of infinite dilution activity coefficients, find the most appropriate solvents for two representative fluorinated precursors likely to be found in textile products. We could determine which ionic liquids were able to interact favourably with perfluorobutyric acid (PFBA) and 6:2 fluorotelomer alcohol (6:2 FTOH). These information could be quantified using isothermal titration calorimetry (ITC) for PFBA in 1-butyl-3-metylimidazolium bis(trifluoromethylsulfonyl)imide, [C4C1Im][NTf2], predicted by COSMO-SAC as a weak solvent, as well as in 1-ethyl-3 methylimidazolium methylsulfonate, [C2C1Im][MeSO3] and 1-butyl-3-methylimidazolium acetate, [C4C1Im][OAc], expected to have strong interactions with the textile additive. Mixing enthalpies of 6:2 FTOH were measured in selected ionic liquids, namely triethylammonium methylsulfonate, [N222H][MeSO3], 1-ethyl-3 methylimidazolium methylsulfonate, [C2C1Im][MeSO3] and acetate, [C2C1Im][OAc]. A proton transfer from PFBA to AcO– (and to a lesser extent from 6:2 FTOH to AcO–) was investigated and described with DFT calculations, 1H NMR analysis and FT-IR spectroscopy.