Anti-fouling ultrafiltration membranes containing polyacrylonitrile-graft-poly(ethylene oxide) comb copolymer additives

Membrane fouling is one of the most important challenges faced in membrane ultrafiltration (UF) operations. In this study, polyacrylonitrile-graft-poly(ethylene oxide) (PAN-g-PEO), an amphiphilic comb copolymer with a water-insoluble polyacrylonitrile (PAN) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains, was used as an additive in the manufacture of novel PAN UF membranes. During casting, the PAN-g-PEO additive segregates to form a PEO brush layer on all membrane surfaces, including internal pores. Wettability, pure water permeability, and resistance to irreversible fouling increased when either the amount of PAN-g-PEO added to the membrane or the PEO content of the comb copolymer was increased. These trends were consistent with measured adhesion forces between the membranes and a carboxylated latex particle probe in an atomic force microscopy (AFM) analysis, and with the near-surface PEO coverage as determined by X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) revealed further effects of additive incorporation on membrane morphology. In 24-h dead-end filtration studies, blend membranes prepared with 20 wt% PAN-g-PEO (comb PEO content: 39 wt%) were found to resist irreversible fouling by 1000 ppm solutions of bovine serum albumin (BSA), sodium alginate, and humic acid, recovering the initial pure water flux completely by a pure water rinse, or a backwash in the case of humic acid. This exceptional anti-fouling performance holds promise for extending UF membrane lifetimes without need for aggressive cleaning procedures.