Chemistry in spinning solutions: Surface modification of PVDF membranes during phase inversion

This article discusses the chemistry in spinning solution of surface-modified poly(vinylidene fluoride) (PVDF) hollow fibre membranes, during phase inversion process. Hydrophilic hollow fibre PVDF membranes have been prepared through the in-situ grafting of spinning solution. The resultant hollow fibre membranes demonstrated improvements on the hydrophilic properties, where the contact angle was substantially reduced. The highest water flux of 406.2L/m(2) h (at 1 bar) was observed on a membrane prepared with ethanol addition and 30 wt% 1-methyl-2-pyrrolidinone (NMP) in water as an internal coagulant. Hollow fibre membranes spun using a wet spinning method (zero air gap) provide higher water flux compared to the ones spun at a higher air gap. By increasing the copolymer contents from 1 wt% to 2 wt%, the water flux increases for both membranes irrespective of their air gaps, while the water flux for hollow fibres with 3 wt% of the copolymer decreases significantly. Morphology of the hollow fibre membranes spun from different air gap changes significantly due to the presence of the hydrophilic graft copolymer, PVDF-g-PEGMA and excess monomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA). The modified hollow fibre PVDF membranes have been also characterised by the FTIR-ATR, SEM, FESEM, bovine serum albumin (BSA) filtration, and tensile strength measurements. The mechanical properties of the modified hollow fibres show relatively smaller tensile strength and higher elongation at break, demonstrating a ductile behaviour. With increasing dope extrusion rate, the tensile strength of the hollow fibre membrane is enhanced due to greater molecular orientation and closer package of the molecules. (c) 2012 Elsevier B.V. All rights reserved.