Preparation of poly(vinyl alcohol-co-ethylene) hollow fiber membranes for high-flux ultrafiltration applications

Poly(vinyl alcohol-co-ethylene) (EVOH) hollow fiber membranes were prepared by isothermal dry-jet wet spinning of dopes containing polyvinylpyrrolidone (PVP), dimethyl sulfoxide (DMSO), and EVOH in water bath at 22 degrees C. DMSO and water are, respectively, a solvent and a non-solvent for EVOH, while PVP, which is water-soluble, enhances pore formation. All membranes are highly asymmetric with macrovoids that extend from the vicinity of both hollow fiber surfaces towards the central region where only interconnected cellular pores are present. Nanopores form on the external surface only in case the dope contains PVP. The internal surface is more porous than the outer one, as the out-diffusing DMSO can quickly reduce the strength of the internal bath during spinning. Water flux measurements indicate an increase-then-decrease trend, consistent with the observed morphological features. The membranes demonstrate attractive ultrafiltration features in the case of blue dextran molecules (2000 kDa); rejection as high as 97.4% at the permeation flux of 116 LMH is observed in the case of hollow fibers prepared from dopes containing 5% PVP.