New Concept for Dual-Layer Hydrophilic/Hydrophobic Composite Membrane for Membrane Distillation
Pages 122-133
Muhammad R. Bilad, Faisal A. Al Marzooqi and Hassan A. Arafat

DOI: http://dx.doi.org/10.6000/1929-6037.2015.04.03.4

Published: 14 September 2015

Abstract: This study presents a new concept of a simple method for the synthesis of dual layer hydrophilic/hydrophobic composite membranes for membrane distillation (MD). The membranes were prepared of poly(vinylidenefluoride) (PVDF) by phase inversion. The synthesis was realized by allowing a full or partial penetration of the polymer solution through one or two non-woven support (NWS) layers. This was achieved by proper selection of a thin NWS having high stiffness, high porosity and low surface tension, in combination with a runny polymer solution and sufficient time gap between casting and coagulation. The applied preparation method was effective in yielding dual layer composite membranes. The first layer atop the NWS was a hydrophilic or slightly hydrophobic one (contact angle (CA) of 88-92º), while the bottom layer beneath the NWS was highly hydrophobic (CA=132-140º). The difference in surface energy between the top and bottom layers originated from a difference in morphology. A smooth and dense top layer is formed as a result of an instantaneous demixing, while a porous and multi-scale network with some degrees of spherulitical structure was formed on the bottom by a delayed demixing mechanism. Direct contact MD (DCMD) results showed that the obtained flux was comparable to other composite MD membranes with high salt rejection. Membrane alignment inside the MD module is a critical element in determining the membrane performance and is shown to significantly increase flux when a top facing feed configuration is used.

Control of Membrane Surface Roughness and Pattern Wave Length by Changing the Nonsolvent (Water) Influx Rate
Pages 15-24
K.C. Khulbe, C.Y. Feng, T. Matsuura, W.J. Lau, E. Halakoo, R. Jamshidi Gohari and A.F. Ismail

DOI: http://dx.doi.org/10.6000/1929-6037.2015.04.01.3

Published: 13 March 2015

Abstract: The control of surface roughness of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS) and cellulose (CE) membranes was attempted by changing the rate of nonsolvent influx in the phase inversion process. PVDF and CE were chosen to represent membranes of high hydrophobicity and hydrophilicity, respectively, while PES and PS were chosen to represent membranes of intermediate hydrophobicity/-philicity. The concentration of sodium chloride (NaCl) in the aqueous coagulation medium was increased from 0 to 1.9 mol/L to decrease the rate of nonsolvent (water) influx in the solvent/nonsolvent exchange process. As well, the effect of polymer concentration and solvent on the surface roughness was investigated with respect to PVDF and PES. It was observed that the membrane surface roughness increased and decreased, respectively, for the hydrophobic PVDF and hydrophilic CE membrane as the rate of nonsolvent influx was decreased. For the PES and PS membranes of intermediate hydrophilic/-philicity, no significant roughness change was observed. The surface roughness tended to increase as the solution viscosity decreased. It was also observed that the pattern wave length of the hydrophobic membrane did not change significantly while that of the hydrophilic membrane increased significantly as the solvent influx rate was reduced. This trend is predictable by considering the shrinking or swelling of the cast polymer solution during the solvent/nonsolvent exchange process.

A Novel Approach to Synthesize Helix Wave Hollow Fiber Membranes for Separation Applications
Pages 8-14
Sung Ryul Park, Jeong-Hoon Kim, Aamer Ali, Francesca Macedonio and Enrico Drioli

DOI: http://dx.doi.org/10.6000/1929-6037.2015.04.01.2

Published: 13 March 2015

Abstract: Helix wave hollow fiber membranes are promising candidate to mitigate fouling and polarization effects in membrane operations. Current study describes a novel but simple approach to synthesize hollow fiber membranes with helix wave configuration. Poly(ether sulfone) (PES) based helix-waved hollow fiber membranes have been fabricated by dry-wet phase inversion process by using asymmetric coagulation conditions. Frequencies of the wave cycle have been observed approximately 20 and the wave length 7.1-7.6mm under the specifically required operating conditions defined by dope solution extrudate rate of 1g/min through 4cm of air-gap heights with 8.6m/min of winding speeds. On the other hand, simple hollow fibers are formed when the elongation force exerted by the winder is much higher than the surface tension of the external coagulant. The process can be useful for making polymer fibers for other applications as well.

Influence of a Microwave Irradiation on the Swelling and Permeation Properties of a Nafion Membrane
Pages 32-39
V.M. Barragán and S. Muñoz

DOI: http://dx.doi.org/10.6000/1929-6037.2015.04.02.1

Published: 08 June 2015

Abstract: The effect of a microwave irradiation at 2450 MHz on the swelling and permeation properties of a Nafion membrane in water and methanol media has been studied. The influence of the irradiation power and the exposure time has been analyzed. The results found show that the irradiation hardly affects the membrane liquid uptake, but it affects the expansion properties of the membrane. The hydraulic permeability coefficient of the unmodified and the irradiated membranes has been experimentally determined. Higher hydraulic permeability has been obtained for the irradiated membranes in both water and methanol, but the degree of increment in permeability coefficient with microwave depends on kinds of permeation liquid. The results have been discussed considering the degradation effect occurring on the membrane hydrophobic matrix, which affects to the membrane elastic properties.

Keywords: Nafion membrane, microwave, hydraulic permeability, swelling, liquid uptake, water, methanol.