Cellulose acetate hollow fiber nanofiltration membrane with improved permselectivity prepared through hydrolysis followed by carboxymethylation

Cellulose acetate (CA) hollow fiber membrane with improved permselectivity for nanofiltration was developed by hydrolysis and carboxymethylation of an original cellulose triacetate semi-permeable membrane. The effects of these modifications on the structure and surface properties were characterized by ATR-FTIR, XRD, SEM and measurements of streaming potential and contact angle. The permeation attributes of the obtained membrane were evaluated through cross-flow permeation tests and the improved permselectivity was also demonstrated through dye removal tests. The results showed that hydrolysis greatly increased the membrane pore size and surface hydrophilicity, but decreased the membrane surface charge, while carboxymethylation had little effect on the membrane pore size, but increased the membrane surface hydrophilicity and negative charge. CA hollow fiber nanofiltration membrane with a pure water permeability of 5.2 l/m2 h bar, NaCl rejection of 66.4% and Na2SO4 rejection of 95.4% could be obtained through modification an original CA semi-permeable membrane having a pure water permeability of 2.3 l/m2 h bar, NaCl rejection of 90.8% and Na2SO4 rejection of 91.5%. Additionally, in treating Congo red and Methyl blue aqueous solutions, the modified CA membrane exhibited improved dye removal rates and higher water fluxes of more than two times compared with the original membrane.

► CA hollow fiber NF membranes with improved permselectivity were developed.
► Permselectivity was improved by controlled hydrolysis and carboxymethylation.
► Hydrolysis increased membrane pore size and hydrophilicity but decreased charge.
► Carboxymethylation increased the hydrophilicity and negative membrane charge.
► Modification had little effect on the morphology structure and crystallinity.