Effect of copolymer concentration on the structure and permeability of temperature-sensitive poly(vinylidene fluoride) hollow fiber membrane

Temperature-sensitive poly(vinylidene fluoride)-grafted-poly(N-isopropylacrylamide) (PVDF-g-PNIPAAm) copolymer hollow fiber membrane was fabricated by dry-wet spinning technique using N,N-dimethyl formamide as solvent and poly(ethylene glycol) as pore-making agent, respectively. The effect of PVDF-g-PNIPAAm copolymer concentration in the spinning solution on the structure and performance of resultant fiber membranes were investigated by field-emission scanning electronic microscopy, pore size measurements, mechanical tests, and filtration experiments. It was found that the microvoid in the inner cross-section of hollow fiber membrane changed to a finger-like structure with the increase of copolymer concentration from 16 to 20%. The increasing copolymer concentration also led to the increase of the inner diameter, outer diameter, and wall thickness and the decrease of mean pore size and porosity. When the permeation temperature was increased from 20 to 45 degrees C, a remarkable reduction of pure water flux and a drastic increase of the retention of bovine serum albumin were observed around 32 degrees C, indicating an obvious temperature-sensitive permeability.