Recyclable\nMembranes through Reversible and Dynamic Crosslinking

Membrane technology is one of the most sustainable methodologies\nin industrial separations due to its low cost, straightforward scale-up\nwith more compact systems, simple operation, and lower energy consumption\nthan traditional thermal separation processes. However, their linear\nlife cycle results in a large amount of membranes being discarded\nevery year, compromising their sustainability and long-term operational\ncost. While recycling membranes could enhance their sustainability,\nit is particularly challenging for solvent-resistant membranes. This\ndifficulty arises from their inherent chemical stability, provided\nby nonreversible cross-linking with permanent covalent bonds in most\ncases. In this work, we propose a reversible and dynamic cross-linking\nwith disulfide bonds by using cysteamine as a cross-linking agent\nto improve the chemical resistance and enable the recyclability of\npoly(ether imide) (Ultem) membranes. The membranes were stable in\ndimethylformamide (DMF) with gel contents above 90% after immersion\nfor a week. Stable permeances of methanol, acetonitrile, and DMF with\nvalues of 1.4, 3.0, and 1.8 L m<sup>–2</sup> h<sup>–1</sup> bar<sup>–1</sup>, respectively, were demonstrated. The cross-linking\nimproved the mechanical properties of the membranes without altering\ntheir microstructure and significantly enhanced the rejection of Direct\nRed 80 (molecular weight of 1373 g/mol) from 75% to 99% in methanol\nsolutions. The method was applied to flat-sheet and hollow fiber membranes.\nThe used membranes were successfully recycled by reducing the disulfide\nbond with 1,4-dithiothreitol, allowing them to be solubilized, purified,\nand cast for membrane fabrication. This study demonstrates the potential\nof integrating dynamic chemistry with membrane science to move toward\nmore sustainable separation processes.