Novel polyamide-imide/cellulose acetate dual-layer hollow fiber membranes for nanofiltration

Shi Peng Sun, Kai Yu Wang, Na Peng, T. Alan Hatton, Tai Shung Chung*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

109 Scopus citations


A novel dual-layer nanofiltration (NF) hollow fiber membrane was fabricated by the simultaneous co-extrusion of Torlon® polyamide-imide and cellulose acetate dopes through a triple-orifice spinneret in a dry-jet wet phase inversion process. For the first time, the nanopores of dual-layer hollow fiber membranes were molecularly designed by controlling the phase inversion process with the aid of various non-solvent additives into the polymer solutions. Compared to ethanol and 2-propanol, the addition of methanol into the dope led to a significantly decreased pore size but dramatically increased pure water permeability. The improved NF performance may be attributed to (1) a controllable thin selective outer layer; (2) a less resistant interface between the outer and inner layers; and (3) a fully porous substructure with reduced transport resistance. In addition to non-solvent additives, spinneret temperature also plays an important role in designing dual-layer hollow fiber membranes with desirable NF performance. When the spinneret temperature was increased from 25°C to 50°C, the mean effective pore radius and the pure water permeability were simultaneously decreased, which was due to the formation of a denser surface skin and a more compact interface between the two layers. In addition to exhibiting a higher rejection of divalent anions than monovalent anions, and a lower rejection of divalent cations at pH 7.0, the newly developed NF dual-layer hollow fiber membranes with methanol as additive has a relatively high pure water permeability of 11.93lm-2bar-1h-1 with a mean effective pore radius of 0.63nm. These concepts hold great potential for the design of tailor-made NF membranes for various industrial applications.

Original languageEnglish (US)
Pages (from-to)232-242
Number of pages11
JournalJournal of Membrane Science
Issue number1-2
StatePublished - Nov 2010
Externally publishedYes


  • Cellulose acetate (CA)
  • Co-extrusion
  • Dual-layer hollow fiber membranes
  • Nanofiltration (NF)
  • Torlon polyamide-imide (PAI)

ASJC Scopus subject areas

  • Biochemistry
  • General Materials Science
  • Physical and Theoretical Chemistry
  • Filtration and Separation


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