Enhanced gas separation performance of dual-layer hollow fiber membranes via substructure resistance reduction using mixed matrix materials

Copoly(4,4′-diphenyleneoxide/1,5-naphthalene-2,2′-bis(3,4-dicarboxylphenyl)hexa fluoro propane diimide) (6FDA-ODA-NDA)/polysulfone (PSF) dual-layer hollow fiber membranes with an enhanced gas separation performance with minimum substructure resistance have been fabricated. Ways to minimize the substructure resistance of 6FDA-ODA-NDA/PSF dual-layer hollow fiber membranes have been extensively investigated in this work. It is found that the addition of Al₂O₃ nanoparticles in the inner layer dope solution can lower the substructure resistance and few cases may achieve 90% of the intrinsic selectivity because of the increased bulk and surface porosity. However, there is a serious limitation on the maximum elongational draw ratio or spinning speed if a traditional dual-layer spinneret is used. A combination of the incorporation of Al₂O₃ nanoparticles in the inner layer dope solution with an indented dual-layer spinneret is the preferred method to effectively minimize the substructure resistance as well as enhance membrane separation performance. Not only does the selectivity can reach above 90% of the intrinsic property of the 6FDA-ODA-NDA dense film, but also the maximum take-up speed as well as elongational draw ratio can be increased to about twofold compared to those fibers produced using the first approach because of a better interface interaction and balanced stress distribution. Both SEM and EDX data support our observations.