Prevention of the capillary contraction of polysulfone based hollow fiber membranes

Hollow fiber ultrafiltration membranes prepared by phase inversion method from polysulfone solutions in dimethylacetamide containing polyethylene glycol 400 as a porogen and polyvinylpyrrolidone K-90 (PVP) as a hydrophilizing additive have been studied. It has been found that the wet hollow fiber membranes are heterogeneous condensation structures characterized by the presence of nonrelaxed internal stresses. Hydrothermal treatment makes it possible to stabilize the fiber structure, and the use of impregnating glycerol solutions can completely preserve the hydraulic permeability of the fiber after drying. Positive effect of the addition of sodium dodecyl sulfate into the impregnating solutions has been revealed, as these additives can mitigate the negative impact of capillary contraction and reduce the concentration of glycerol. An abnormal effect of the recovery of the porous structure and permeability of capillary-contracted polysulfone hollow fiber membranes after their treatment with dilute solutions of polyethylene glycols (PEGs) with M = 6000–20000 has been established. This effect has been assumed to be due to the wedging action of PEG as a result of interaction with the hydrophilizing additive polyvinylpyrrolidone.