Blend polyethersulfone/zirconium oxychloride octahydrate membranes crosslinked by polyvinyl alcohol layer for high saline water desalination

Mixed matrix membranes were prepared by blending polyethersulfone with zirconium oxychloride octahydrate (ZOH) solution, and coating by polyvinyl alcohol layer. Different analyses were applied in the prepared membranes. Membranes performances were examined using different salty solutions concentrations (5000, 10,000 and 20,000 mg/L) and a real sample from highly concentrated seawater (brine) of 1,30,900 mg/L. The results indicate that blending polyethersulfone with 1.5% ZOH and coating with polyvinyl alcohol (PVA) cross-linking layer (M4) provides salt rejection of 99.9% with permeate flux of 32.4 L/m2.h for the salt solution of 5000 mg/L, while salt rejection was 92% with permeate flux of 11.1 L/m2.h for the salt solution of 1,30,900 mg/L. The results indicate enhancement in the hydrophilicity of the membranes especially after coating by the PVA layer and increasing the ZOH%, such as the high permeate flux and the lowest contact angle of prepared membrane M4 (1.5% ZOH) which was 39.7°. A long time experiment was applied on the prepared membrane (M4), where the results indicate that the permeate flux for a long time was approximately fixed for 120 h, which indicates that the membrane can be considered as a self-cleaning membrane.

Performance of Acacia Gum as a Novel Additive in Thin Film Composite Polyamide RO Membranes

Novel thin film composite (TFC) polyamide (PA) membranes blended with 0.01–0.2 wt.% of Acacia gum (AG) have been prepared using the interfacial polymerization technique. The properties of the prepared membranes were evaluated using contact angle, zeta potential measurements, Raman spectroscopy, scanning electron microscopy, and surface profilometer. It was found that the use of AG as an additive to TFC PA membranes increased the membrane’s hydrophilicity (by 45%), surface charge (by 16%) as well as water flux (by 1.2-fold) compared with plain PA membrane. In addition, the prepared PA/AG membranes possessed reduced surface roughness (by 63%) and improved antifouling behavior while maintaining NaCl rejection above 96%. The TFC PA/AG membranes were tested with seawater collected from the Arabian Gulf and showed higher salt rejection and lower flux decline during filtration when compared to commercial membranes (GE Osmonics and Dow SW30HR). These findings indicate that AG can be used as an efficient additive to enhance the properties of TFC PA membranes.

The effect of fluorinated surface modifying macromolecules on the surface morphology of polyethersulfone membranes

Polyethersulfone (PES) has been recently adopted for membrane materials in applications such as ultrafiltration and haemodialysis. As a biomaterial, the factors which affect the blood compatibility of PES membranes include surface energetics, hydrophobicity, and surface morphology. Surface fluorination of materials has been found to create surfaces with improved blood compatibility and chemical stability. One novel approach to generating fluorinated polymer surfaces has included the use of fluorinated surface modifying macromolecules (SMMs). These macromolecules have been reported to establish fluorinated functional groups at surfaces of polymeric materials without significantly affecting the physical properties of the base polymer. However, to date there has been relatively little information published on the nature of the surface structure for PES materials containing these SMMs. In this study, synthesized SMMs with varying chemical compositions were characterized and blended with PES, and fabricated into flat sheet membranes. The bulk thermal transitions of PES materials were not significantly altered by the addition of 4 wt% SMMs. Contact angle data showed that the addition of SMMs in PES created more hydrophobic surfaces, accompanied by an increase in surface heterogeneity. X-ray photoelectron spectroscopy studies confirmed the presence of elemental fluorine at the surface. Through microscopy studies, it was shown that surface modification was achieved by the migration of SMM concentrated microdomains to the air-membrane interface. The generated microdomains (approximately 1-2 microm in diameter) are dispersed within the top 8 microm of the surface. The concentration of microdomains was gradually depleted from the surface to the bulk of the membrane. A schematic of the morphology for SMMs within the PES membrane surface was proposed.