Evolution of the precipitation kinetics, morphology, and permeation performance of phenolphthalein poly(ether sulfone) hollow-fiber membranes with polyvinylpyrrolidones of different molecular weights as additives

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Abstract

Phenolphthalein poly(ether sulfone) (PES-C) hollow-fiber ultrafiltration (UF) membranes were fabricated by wet spinning and dry-jet/wet spinning (10-cm air gap) processes with polyvinylpyrrolidones (PVPs) of different molecular weights as additives. Light transmittance experiments were performed to obtain insight into the precipitation kinetics of PES-C/PVP/N-methyl-2-pyrrolidone (NMP) dope solutions. The morphology and permeation performance of the prepared PES-C hollow-fiber membranes were well characterized and elucidated with scanning electron microscopy and UF experiments in addition to the precipitation kinetics. The thermal and mechanical properties of the membranes were also studied. Experiments demonstrated that all PES-C/PVP/NMP dope solutions experienced instantaneous demixing with pure water as the coagulant, and the precipitation rate decreased as the molecular weight of PVP increased. A double, fingerlike structure occurred in the PES-C hollow-fiber membranes spun with PVPs of low molecular weight (10,000, 24,000, or 58,000) as additives; however, a spongelike structure occurred in the PES-C membranes with PVP with a molecular weight of 1,300,000 because of its very low precipitation rate. The pure water permeation (PWP) flux decreased and the rejection of lysozyme increased for the prepared PES-C membranes as the molecular weight of PVP increased. The largest PWP flux of 149 L m−2 h−1 bar−1 was acquired for dry-jet/wet-spun PES-C membranes with PVP with a molecular weight of 10,000 as an additive. The rejection of bovine serum albumin for the prepared PES-C membranes was greater than 98%, and the rejection of lysozyme ranged from 47.1 to 89.4%; this indicated typical UF membranes. The decomposition temperature of the PES-C membranes containing PVP was lower than that of the original polymer and decreased as the molecular weight of PVP increased. The break strain and the elongation at break were enhanced as the PVP molecular weight increased. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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