The hidden challenge of membrane recycling: how drying affects membrane layers?

Improper management or storage after discharge of thin film composite membranes are challenging due to potential drying, which may affect the integrity of the material, decrease the performance and impede their potential recycling for second-hand applications. The impact of drying onto the different layers of thin film composite membranes remain empirical and poorly studied. This work systematically assessed the impact of the drying phenomena on the physical changes across poly(amide) and poly(sulfone) layers by applying drying/rewetting protocols consisting of (1) soaking the membrane in a solvent, (2) drying at 60 °C and (3) rewetting with ethanol. After each step, membrane performance as well as surface characterization were assessed. Severe loss of permeabilities, up to 65 and 90 % for the poly(amide) and the poly(sulfone) layer respectively, were observed. Drying effect was demonstrated to be quickly reversible (1 min soaking in ethanol) for the poly(amide) layer even over several drying-rehydration cycles. Permeability of the poly(sulfone) layer appeared to be permanently impacted due to a possible irreversible surface shrinkage and pores collapsing showing permanent changes in the poly(sulfone) layer. These findings highlight the importance of studying membrane drying to prevent further performance loss, optimize material lifetime, ensure continuity of operation, and enable membrane recycling. • Drying leads to a severe decrease of permeability in TFC membranes • Dried Poly(amide) layer can be partially to fully recovered after ethanol soaking. • Dried Poly(sulfone) layer is affected permanently by drying. • Drying provokes permanent cracks on PSf membrane surface • Avoiding drying is crucial for potential membrane recycling