Hollow fiber formation using Lewis acid: Base complex in the polymer solution

In the present work, hollow fiber formation was investigated by using Lewis acid:base complexes in the polymer solution. The studied systems consisted of poly(ether sulfone); N-methyl-2-pyrrolidone (NMP) as solvent and Lewis base, and acetic, propionic, n-caproic, and adipic acids as additives and L ewis acids. Bore liquid was formed by water/NMP solutions, as well as vasel ine; whereas water was used as external precipitation bath. The spinneret a nd precipitation bath distance (i.e., air gap) also varied. The membranes w ere characterized by scanning electron microscopy and pure gas permeation t ests. The influence of the complex dissociation rate was observed mainly wh en a reduction to water inflow from the bore liquid to the polymer solution occurred, because in this case, dissociation rate was inhibited. Therefore , stability was favored in the sublayer for a longer period, allowing macro void formation. These results are also evidenced by the permeability coeffi cients, which increased as fast as the polymer solution reaches water (i.e. , the kinetics of precipitation was accelerated). (C) 20012001 John Wiley & Sons, Inc.