Overlooked permeation resistance changes of NF membranes during heat curing: Glycerol post–treatment as a structural and kinetic modulator

Glycerol post-treatment after interfacial polymerization (IP) is a critical step in manufacturing nanofiltration (NF) membranes at an industrial scale, yet its mechanism of action on the polyamide (PA) layer and the substrate is not fully elucidated. To systematically uncover the internal mechanisms, we fabricated uncured, heat-cured, and glycerol-cured (NF-GP) membranes on commercial ultrafiltration supports. The results showed that glycerol's high hydrophilicity, viscosity, and boiling point impart structural support and a water-locking effect in the membrane pores, thus minimizing pore shrinkage and collapse. Consequently, the NF-GP membrane demonstrated a thickness reduction of 26.4 %, a permeance decay of only 16.3 %, a DOC rejection of 89.8 %, and a smooth surface. Moreover, glycerol preserved substrate porosity (16.3 %) and enhanced stability during heat curing. Our analysis also correlated surface roughness with intramembrane humidity, pore wall stress, and the composition of the internal liquid layer. A quantitative resistance-in-series model further revealed that the PA layer contributes over 95 % of the total resistance, governing transmembrane molecular transport. These findings offer valuable theoretical and mechanistic insights for tailoring glycerol post-treatment to fabricate high-performance NF membranes industrially.