Membrane technology has been used in water purification for decades. However,
membrane fouling remains a limiting factor. One way to control fouling is through
surface modification. Several studies report that increasing surface hydrophilicity can
reduce membrane fouling. Surface modification via physical coating (i.e., thin-film
composite membrane) was explored in this research to prevent membrane fouling.
Before making thin-film composite membranes, it was important to study
structure/property relations in a series of potential coating materials. This research aims
to contribute to a better fundamental understanding of the structure/property relations
which govern water transport, rejection of model foulants (i.e., emulsified oil droplet or
protein), and fouling characteristics in hydrogels based on poly(ethylene glycol)
diacrylate (PEGDA) and N-vinyl-2-pyrrolidone (NVP).
Crosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by
UV-induced photopolymerization of PEGDA crosslinker in the presence of varying
amounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS)
when the water content of the prepolymerization mixture was greater than 60 wt%.
Visible light absorbance measurements, water uptake, water permeability, and salt kinetic
desorption experiments were used to characterize the structure of these phase-separated,
crosslinked hydrogels. The films with PIPS exhibited a porous morphology in cryogenic
scanning electron microscope (CryoSEM) studies. Dead-end filtration experiments using
deionized water and bovine serum albumin (BSA) solutions were performed to explore
the fundamental transport and fouling properties of these materials. The total flux of pure
water through the films after prior exposure to BSA solution was nearly equal to that of
the as-prepared material, indicating that these PEGDA films resist fouling by BSA under
the conditions studied.
Crosslinked NVP free-standing films were prepared by UV-induced
photopolymerization in the presence of water, with NVP as the monomer and
N,N’-methylenebisacrylamide (MBAA) as the crosslinker. A series of crosslinked films
were polymerized at various prepolymerization water contents, NVP/MBAA ratios and at
various levels of UV light intensity in the polymerization. Like PEGDA, the NVP films
also underwent phase-separation during polymerization. The influence of monomer/
crosslinker ratio, prepolymerization water content, and UV intensities on membrane
morphology and water transport was characterized with CryoSEM, bio-atomic force
microscope (Bio-AFM) and dead-end filtration. Molecular weight cutoff (MWCO)
measurements were used to characterize the sieving property of crosslinked NVP films
polymerized at different UV intensities. UV intensity was found to have an impact on the
interconnectivity of crosslinked membranes. Finally, tests of fouling resistance to protein solution (bovine serum albumin) and oily water emulsion were performed. The NVP
crosslinked films had good protein and oily water fouling resistance.
Overall, both crosslinked PEGDA and NVP films exhibit fouling resistance to
oily water emulsions or protein solution. NVP films had more porous structure and
higher water permeability than did PEGDA films, while the more compact structure of
PEGDA films led to better rejection of model foulants (e.g., protein) than in NVP films.
Based on different applications (e.g., oil/water separation, protein filtration), different
coating materials must be chosen according to the membrane morphology, transport
property, and rejection of model foulants to achieve the highest water flux and foulant rejection in membranes used for water purification. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/6662 |
| Date | 23 October 2009 |
| Creators | Wu, Yuan-hsuan |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Format | electronic |
| Rights | Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. |
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