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.