Formation of defect-free 6FDA-DAM asymmetric hollow fiber membranes for gas separations
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AbstractThis paper reports the formation of defect-free 6FDA-DAM asymmetric hollow fiber membranes. 6FDA-polyimides are of great interest for advanced gas separation membranes, and 6FDA-DAM polyimide is a representative polymer in this family with attractive dense film properties for several potential applications. The work reported here for the 6FDA-DAM polyimide provides insight for the challenging fabrication of defect-free asymmetric hollow fiber membranes for this class of 6FDA-polyimides, which behave rather different from lower free volume polymers. Specifically, the 6FDA based materials show relatively slow phase separation rate in water quench baths, which presents a challenge for fiber spinning. For convenience, we refer to the behavior as more "non-solvent resistant" in comparison to other lower free volume polymers, since the binodal phase boundary is displaced further from the conventional position near the pure polymer-solvent axis on a ternary phase diagram in conventional polymers like Matrimid® and Ultem®. The addition of lithium nitrate to promote phase separation has a useful impact on 6FDA-DAM asymmetric hollow fiber formation. 6FDA-DAM phase diagrams using ethanol and water as non-solvent are reported, and it was found that water is less desirable as a non-solvent dope additive for defect-free fiber spinning. Phase diagrams are also reported for 6FDA-DAM dope formulation with and without the addition of lithium nitrate, and defect-free asymmetric hollow fiber membranes are reported for both cases. The effect of polymer molecular weight on defect-free fiber spinning was also investigated. Gas transport properties and morphology of hollow fibers were characterized. With several thorough case studies, this work provides a systematic guideline for defect-free fiber formation from 6FDA-polymers. © 2014 Elsevier B.V.
CitationXu L, Zhang C, Rungta M, Qiu W, Liu J, et al. (2014) Formation of defect-free 6FDA-DAM asymmetric hollow fiber membranes for gas separations. Journal of Membrane Science 459: 223–232. Available: http://dx.doi.org/10.1016/j.memsci.2014.02.023.
SponsorsThis work was supported by The Dow Chemical Company. The authors acknowledge the additional support provided by King Abdullah University of Science and Technology (KAUST), Discussions with Mark Brayden and Marcos Martinez are greatly appreciated.
JournalJournal of Membrane Science