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An Innovative Surface Modification Technique for Antifouling Polyamide Nanofiltration Membranes In this study, we developed a novel surface coating technique to modify the surface chemistry of thin film composite (TFC) nanofiltration (NF) membranes, aiming to mitigate organic fouling while maintaining the membrane’s permselectivity. We formed a spot-like polyester (PE) coating on top of a polyamide (PA) TFC membrane using mist-based interfacial polymerization. This process involved exposing the membrane surface to tiny droplets carrying different concentrations of sulfonated kraft lignin (SKL, 3, 5, and 7 wt %) and trimesoyl chloride (TMC, 0.2 wt %). The main advantages of this surface coating technique are minimal solvent consumption (less than 0.05 mL/cm2) and precise control over interfacial polymerization. Zeta potential measurements of the coated membranes exhibited enhancements in negative charge compared to the control membrane. This enhancement is attributed to the unreacted carboxyl functional groups of the SKL and TMC monomers, as well as the presence of sulfonate groups (SO3) in the structure of SKL. AFM results showed a notable decrease in membrane surface roughness after polyester coating due to the slower diffusion of SKL to the interface and a milder reaction with TMC. In terms of fouling resistance, the membrane coated with a polyester composed of 7 wt % SKL showed a 90% flux recovery ratio (FRR) during Bovine Serum Albumin (BSA) filtration, showing a 15% improvement compared to the control membrane (PA). PE-coated membranes provided stable separation performance over 40 h of filtration. The sodium chloride rejection and water flux displayed minimal variations, indicating the robustness of the coating layer. The final section of the presented study focuses on assessing the feasibility of scaling up and the cost-effectiveness of the proposed technique. The demonstrated ease of scalability and a notable reduction in chemical consumption establish this method as a viable, environmentally friendly, and sustainable solution for surface modification.T10-A02 University of Alberta Publication 2024-07-03 T10-A02 pH-Fractionated lignin enables high-selectivity, chlorine-tolerant polyester thin-film composite nanofiltration membranes olyamide thin-film composite (TFC) membranes provide high permeability and strong ion rejection in nanofiltration and reverse osmosis, but oxidants like chlorine can impair their long-term performance. To overcome this, alternative chemistries are needed to improve durability while maintaining separation efficiency. Lignin-based polyester TFC membranes are promising, offering better antifouling and chlorine resistance. However, their lower salt rejection hampers wider adoption. Here, we used distinct molecular-weight fractions of lignin to fabricate polyester TFC membranes and assessed how fraction-specific physicochemical properties govern membrane structure and performance. Lignin was separated into five fractions (B1–B5) via pH fractionation. Among the resulting membranes, the B4-derived TFC (M-B4) achieved the best overall performance, delivering 98% rejection of Na2SO4 and 41% rejection of NaCl with a water flux of 45 LMH. The B4 fraction isolated at pH 3.1, with a smaller particle size and a high phenolic hydroxyl content (2.1 mmol g−1), yielded a highly crosslinked polyester with increased hydrophilicity and surface roughness. M-B4 also exhibited excellent antifouling performance, with a flux recovery ratio (FRR) of 99% after three cycles, and strong operational stability, with only a 2% reduction in Na2SO4 rejection and a 5.5% decrease in water flux after 12 h of extended filtration. Additionally, after four days of chlorine exposure, Na2SO4 rejection decreased by just 2%, while water flux increased by 9%. Finally, we performed a cost analysis for large-scale manufacturing and benchmarked the estimated production cost against reported prices for conventional polyamide TFC membranes. This innovative yet simple strategy positions lignin-based polyester membranes as sustainable and efficient alternatives to polyamide membranes.T10-A02 University of Alberta Publication 2026-04-15 T10-A02 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.
T10-A02 University of Alberta Publication 2025-10-15 T10-A02
