Lignin depolymerization: A sustainable strategy to enhance the separation performance of biopolymeric polyester membranes

Membrane technology remains essential for water treatment and desalination. While polyamide thin-film composite (TFC) membranes dominate the industry, their susceptibility to fouling reduces efficiency and shortens operational lifespan. Advanced chemical modification strategies have been developed to overcome this challenge, aiming to improve membrane performance and durability. Polyester-based TFC membranes offer a promising alternative, providing a negatively charged surface. However, their lower salt rejection than polyamide membranes remains a key limitation. In this study, we investigated the application of depolymerized lignin, a naturally abundant biopolymer, as a phenolic monomer for fabricating polyester TFC membranes. The native lignin has a much larger molecular size compared to conventional monomers, which limits its diffusion and reactivity during membrane formation. We utilized a microwave-assisted depolymerization technique to fractionate lignin into smaller moieties, resulting in oligomeric/monomeric lignin with a lower molecular mass and higher reactive sites. This approach enabled faster membrane fabrication and significantly improved membrane performance. The membranes fabricated by depolymerized lignin exhibited substantially improved salt rejection, achieving up to 98.8 % for sodium sulfate and 54 % for sodium chloride removal. The developed membranes exhibited excellent antifouling properties, as demonstrated by sodium alginate fouling tests, with a flux recovery ratio of over 85 %. This research presents an innovative approach to enhancing non-polyamide TFC membranes, opening up new possibilities for eco-friendly and efficient membrane technologies in practical desalination applications. • Depolymerized lignin enables fast fabrication of polyester TFC membranes. • Achieved 98.8 % Na 2 SO 4 and 54 % NaCl rejection with modified membranes. • Microwave-assisted depolymerization enhances lignin reactivity and diffusion. • Membranes show >85 % flux recovery in sodium alginate fouling tests. • Eco-friendly alternative to polyamide membranes with improved antifouling.