Dynamic Covalent Chemistry Enabled Closed-Loop Recycling of Thermally Modified Polymer Membrane.

The increasing demand for sustainable solutions to oil-water separation and end-of-life membrane disposal has prompted the development of recyclable membrane technologies. In this study, we present an innovative approach to fabricating closed-loop, recyclable nanofibrous membranes (RFMs) utilizing reversible covalent networks based on the Diels-Alder reaction. A methacrylate-based copolymer was synthesized via free radical polymerization, combining hydrophobic monomers for enhanced separation performance, with furan-functionalized monomers for recyclability. This copolymer was electrospun into a porous substrate and cross-linked with bismaleimide cross-linkers to form a dynamic covalent network. By incorporating postthermal modification to the nanofibrous membrane, the hydrophobicity and the membrane porosity can be optimized. The resulting RFM exhibited outstanding oil-water separation capabilities, achieving a pure oil flux of up to 1,187 LMH with a separation efficiency up to 99% in water-oil emulsions, as demonstrated in tests with dichloromethane and other oils. Notably, the RFMs maintained structural and chemical stability after two recycling cycles, with recycled membranes retaining fluxes of 474-1,187 LMH and efficiencies of 98.8-99.5%. Thermal and mechanical characterizations confirmed the great stability of the membranes, with the Diels-Alder reaction enabling depolymerization and reformation of the network without causing significant degradation. Additionally, the RFMs were recycled the third time, maintaining the fluxes (752 to 823 LMH) from the previous generation with a slight decrease in separation efficiency in dichloromethane-water emulsion separation (98.3 to 97%). By integrating dynamic covalent chemistry with scalable fabrication methods, RFMs represent a transformative step toward a circular economy in oil-water separation and broader wastewater treatment and resource recovery.