Formation of porous poly(vinylidene fluoride) membranes with symmetric or asymmetric morphology by immersion precipitation in the water/TEP/PVDF system

Dar Jong Lin, Hsu Hsien Chang, Tzung Chin Chen, Yi C. Lee, Liao Ping Cheng

Research output: Contribution to journalArticle

101 Citations (Scopus)

Abstract

The phase equilibrium boundaries of the membrane forming system, water/triethyl phosphate (TEP)/PVDF, at 25 °C were determined experimentally using cloud-point and equilibrium absorption methods. Based on the phase diagram, appropriate dope and bath compositions were selected to prepare microporous membranes by means of the isothermal immersion-precipitation technique. As a metastable casting dope with respect to crystallization was adopted, the formed membranes exhibited a uniform cross-section composed of interlocked crystal elements coexisting with the network of continuous pores, as was revealed by high resolution FESEM imaging. Morphologies of the membranes' top surfaces were found to depend heavily on the bath strength, which was controlled by the TEP content. By changing the bath gradually from pure water to 70% TEP, the top surface evolved from a dense skin (asymmetric membrane) to a totally porous morphology (symmetric membrane). Wide angle X-ray diffraction analysis indicated that PVDF crystallized into α-type structure for all of the synthesized membranes. The crystallinity as determined from diffraction peak deconvolution was ≈65%, which value was confirmed by Differential Scanning Calorimetry (DSC). The obtained thermograms also showed a similar melting peak temperature (Tm ≈ 169 °C) for all membranes. Furthermore, water fluxes and tensile strengths of the membranes were measured. The results were found to correlate with the morphologies of the membranes.

Original languageEnglish
Pages (from-to)1581-1594
Number of pages14
JournalEuropean Polymer Journal
Volume42
Issue number7
DOIs
Publication statusPublished - Jul 2006
Externally publishedYes

Fingerprint

vinylidene
submerging
fluorides
phosphates
Phosphates
membranes
Membranes
Water
water
baths
polyvinylidene fluoride
triethyl phosphate
thermograms
Deconvolution
Crystallization
diffraction
Phase equilibria
tensile strength
X ray diffraction analysis
Phase diagrams

Keywords

  • Crystallization
  • Membrane
  • Phase separation
  • Poly(vinylidene fluoride)

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics

Cite this

Formation of porous poly(vinylidene fluoride) membranes with symmetric or asymmetric morphology by immersion precipitation in the water/TEP/PVDF system. / Lin, Dar Jong; Chang, Hsu Hsien; Chen, Tzung Chin; Lee, Yi C.; Cheng, Liao Ping.

In: European Polymer Journal, Vol. 42, No. 7, 07.2006, p. 1581-1594.

Research output: Contribution to journalArticle

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AU - Cheng, Liao Ping

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AB - The phase equilibrium boundaries of the membrane forming system, water/triethyl phosphate (TEP)/PVDF, at 25 °C were determined experimentally using cloud-point and equilibrium absorption methods. Based on the phase diagram, appropriate dope and bath compositions were selected to prepare microporous membranes by means of the isothermal immersion-precipitation technique. As a metastable casting dope with respect to crystallization was adopted, the formed membranes exhibited a uniform cross-section composed of interlocked crystal elements coexisting with the network of continuous pores, as was revealed by high resolution FESEM imaging. Morphologies of the membranes' top surfaces were found to depend heavily on the bath strength, which was controlled by the TEP content. By changing the bath gradually from pure water to 70% TEP, the top surface evolved from a dense skin (asymmetric membrane) to a totally porous morphology (symmetric membrane). Wide angle X-ray diffraction analysis indicated that PVDF crystallized into α-type structure for all of the synthesized membranes. The crystallinity as determined from diffraction peak deconvolution was ≈65%, which value was confirmed by Differential Scanning Calorimetry (DSC). The obtained thermograms also showed a similar melting peak temperature (Tm ≈ 169 °C) for all membranes. Furthermore, water fluxes and tensile strengths of the membranes were measured. The results were found to correlate with the morphologies of the membranes.

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