Correlating polymer solution and membrane fabrication with morphological and permeation properties of cellulose acetate ultrafiltration membranes

Cellulose acetate (CA) membranes were prepared by phase inversion using three fixed solvent compositions (30/53, 31/52 and 35/48 wt% of formamide/acetone) while varying the air exposure time prior to immersion (0, 10, and 30 s). The influence of the percentage of formamide and evaporation time on the membrane structure and performance was investigated through scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterization, pure water permeation, and molecular weight cut-off (MWCO) measurements. Results demonstrated that evaporation time was a key factor in controlling the membrane morphology. Short evaporation times favored fast demixing and the formation of macrovoids, while longer evaporation times (30 s) suppressed these defects and produced smoother selective layers. The CA(35)-30 membrane exhibited the most favorable properties, including a water permeability of 36.0 L/h/m 2 /bar, an MWCO of 35.0 kDa, low surface roughness (RMS = 1.81 nm), and an asymmetric structure free of macrovoids and surface stripes.