Preparation and characterization of polyacrylonitrile ultrafiltration membranes

Asymmetric polyacrylonitrile (PAN) ultrafiltration (UF) membranes are prepared from three kinds of coagulant: water, aqueous solution of sodium chloride (NaCl) and aqueous solution of sodium carbonate (Na2CO3), using dimethylacetamide (DMAC) as solvent and calcium chloride (CaCl2) as additive by phase inversion method. The membranes are characterized in terms of the pure water flux, molecular weight cut-off (MWCO) profile and direct field emission scanning electron microscopy (FESEM) observations. The addition of CaCl2 to the casting solution, up to 3 wt.%, increases the resulting membrane permeability while maintaining their retentive properties. A decrease of the permeability and retention properties is observed when the coagulation bath is aqueous solution of NaCl. Na2CO3 in the coagulation bath reacts with CaCl2 in the casting solution and produces precipitate of CaCO3. The effect of Na2CO3 concentration on the PAN membrane permeability and retention properties is examined. It is found that the pure water fluxes of the PAN membranes increase drastically when the concentration of Na2CO3 is high enough.