College Papers

Physical had enhanced fouling resistance. However, the coating

Physical
surface modification of TFC RO membrane has two sub category which is surface
adsorption and surface coating. In Table 1, different physical surface
modification is summarised in order from past to present.

Researchers
have carried out surface modification of RO membranes by adsorption of compounds
such as surfactants 29 and charged polyelectrolytes 31.

In
year 1998, Wilbert et al. 29 applied a homologous series of polyethyleneoxide
(PEO) surfactants with either octylphenol or polypropylene oxide head groups
(T-X series and P series) to modify the surface of commercial polyamide TFC RO
membranes. The strategy in that study combined the benefits of increased
hydrophilicity with steric hindrance by adsorbing surfactants. The results
showed that surfactants decreased the roughness of membranes without a large
change in zeta potential and the membranes exhibited improved antifouling
property in a vegetable broth solution compared to unmodified membrane.

In
2006, Louie et al. 30 performed physical coating study of commercial
polyamide RO membranes with PEBAX-1657, which was a very hydrophilic block
copolymer of nylon-6 and PEG. The coating greatly reduced surface roughness
without significant change in contact angle. During a long-term (106 day)
fouling test with an oil/surfactant/water emulsion, the rate of flux decline
was slower for coated than for uncoated membranes that showed the coated
membranes had enhanced fouling resistance. However, the coating resulted in
large water flux reduction, especially for high-flux RO membranes 30.

In
2009, Yong Zhou et al. 31 used surface adsorption method by using charged
polyelectrolytes adsorption for surface modification of RO membrane. The
modification was done by electrostatic self deposition of polyethyleneimine
(PEI) (a branched hydrophilic cationic polyelectrolyte) on the membrane
surface, and the modified membrane showed significantly improved antifouling
properties. The charge reversal on the membrane surface due to the application
of the polyethyleneimine layer was shown to increase the fouling resistance of
the membrane to cationic foulants because of the enhanced electrostatic
repulsion, and the increased surface hydrophilicity would help minimize the flux
reduction. In same year, Sagle et al. 32 investigated the effect of coating
of a series of cross-linked PEG-based hydrogels on the RO membranes. NaCl
rejection for both uncoated and coated membranes was 99.0% or greater while the
water flux was decreased for coated membranes than that of uncoated membranes. Surfactant
fouling of DTAB and SDS has been carried out which showed that lower salt
rejection for DTAB fouled membranes and SDS-fouled membranes had higher salt
rejection than membranes not exposed to surfactants. In both fouling experiments,
coated membranes had less flux decline than uncoated AG RO membranes.

In 2010, Y. Kwon et
al. 33 the homopolymer poly(ethylene glycol) acrylate (PEGA) was used as
surface coating to enhance antifouling property of RO membranes. PEGA coated RO
membranes were cross-linked by the glutaraldehyde (GA) solution to enhance the
durability of the coating layer. After the surface modification, the RO
membranes showed a lower surface roughness, more hydrophilicity, and better performance
compared to the unmodified RO membranes.