Fouling resistant, high flux nanofiltration membranes from polyacrylonitrile-graft-poly(ethylene oxide)

Membranes possessing both fouling resistance and permeate size cut-offs in the nanometer range would open membrane processes to numerous molecular separations in the biochemical, pharmaceutical and food industries. This study describes the preparation of novel thin film composite (TFC) nanofiltration (NF) membranes with the above properties, where the selective layer is a dense coating of the amphiphilic comb copolymer polyacrylonitrile-graft-poly(ethylene oxide) (PAN-g-PEO). PAN-g-PEO is synthesized by free-radical polymerization using a macromonomer method, and solution coated onto a PAN ultrafiltration (UF) membrane support. Upon coagulation of the coating, microphase separation occurs between the hydrophobic PAN backbone and hydrophilic PEO side chains, as determined by differential scanning calorimetry (DSC). Transmission electron microscopy (TEM) reveals the formation of an interconnected network of PEO domains that act as water-permeable nanochannels and provide the size-based separation capability of the membrane. In filtration studies, the pure water permeability of PAN-g-PEO TFC NF membranes was found to be 85 ± 25 L/m2 h MPa, over 4 times that of a commercial NF membrane control. The permeate size cut-off was determined by the filtration of a series of rigid dye molecules to be less than 1 nm, and the fractionation of a mixture of two anionic dyes, Congo Red and Ethyl Orange, was demonstrated. Further, the membrane showed complete resistance to fouling, defined as flux loss that cannot be recovered by a water rinse, by 1 g/L bovine serum albumin (BSA) in a 24-hour dead-end filtration experiment, demonstrating the promise of these membranes for biomolecule separations.