Interfacial Polymerization Preparation Of The Small Aperture Composite Ultrafiltration Membrane And Its Performance,

Commerical ultrafiltration membranes with small pore size are uaually manufactured by phase inversion method. The obtained asymmetric ultrafiltration membranes possess shortcomings such as relatively dense selective layer, low solvent permeability, poor compression resistance, as well as hydrophobicity, which limit the applications of the ultrafiltation membranes. In this paper, we focused on the preparation and properties of thin-film composite ultrafiltration (TFC UF) membrane with small molecular weight cut-off (MWCO) and high permeability by interfacial polymerization process, and the factors controlling the pore size of the resultanant membrane as well. The thin-film composite ultrafiltration membranes with small pore size were prepared through the interfacial polymerization of piperazine (PIP) and macromolecular polyvinylamine (PVAm) with trimesoyl chloride (TMC) on the porous polysulfone (PSF) support membrane. The surface properties of the resulting TFC membranes were characterized by using Attenuated total reflectance infrared (ATR-IR), Scanning electron microscopy (SEM), X-Ray photoelectron spectra, Atomic force microscopy (AFM), and contact angle measurements. The separation properties of the obtained membranes in terms of solute rejection rate, water permeability and molecular weight cut-off (MWCO) were studied through cross-flow permeation tests with aqueous solution containing different solutes such as salts, PEG600 (Mw= 600 Da), PEG1000 (Mw= 1000 Da), PEG2000 (Mw= 2000 Da), PEG4000 (Mw= 4000 Da) and PEG6000(Mw= 6000 Da) under certain operating conditions (pressure, solute concentration). The resultant membranes were also used to separate the heparin sodium (Mw= 4000 Da) aqueous solution and explored the prospects of their applications in the treatment of dyeing wastewater.The results of ATR-IR, SEM and XPS showed that an active skin layer had been formed on the surface of the polysulfone suppot membrane through the reaction of PIP, PVAm and TMC. The thin film contained three types of polyamides, namely polypiperizineamide from the reaction of PIP and TMC, polyvinylamide from the reaction of PVAm and TMC, and aromatic-aliphatic polyamide from the reaction of PIP, PVAm and TMC. It was found that the membrane surface properties could modulated by varying the weight ratio of PIP to PVAm, as well as the monomer concentrations of the reaction solutions. The surface roughness of the resultant composite membrane decreased with increase of PVAm content in the aqueous solution. The surfaces of the composite membranes were hydrophilic,and their contact angles were much lower than those of the support polysulfone membranes. The results of surface zeta potential measurements revealed that the surface of the resulting composite membranes were amphoteric. The membrane surfaces had an isoelectric point (IEP) between pH 3 and 4, and were positively charged at pHs lower than 3.0 and negatively charged at pHs higher 4.0.The study of the separation properties of the resultant membranes indicated that the composite membranes had good permeability and their pore size could be easily adjusted by varying the content of PVAm in the aqueous phase. The pore size of the resultan composite ultrafiltration membrane increased as the content of PVAm in the aqueous phase increased. Composite membranes with MWCO of about 1000, 3100, and 5000 Da possessed an improved water permeability of 27.2, 30.8 and 35.2 l/m2·h·bar, respectively, which were superior to those reported data of the commercial asymmetric UF membranes with the comparable MWCO. Moreover, the retention rate of the resultant composite UF membranes for charged solute was determined by both the size exclusion effect and Donnan effect. The retention rate of the UF membrane with MWCO of about 3100 Da for low molecular heparin sodium (Mw= 4000) increased from 88.56 % to 99.11 % when the feed pH increased from 3 to 11.The research of the composite membranes prepared in this study in treating dyeing wastewater were conducted through cross-flow permeation tests with aqueous solutions containing NaCl and different types of dyes such as Methyl red, Methylene blue, Rhodamine B, Methyl blue and Congo red. For the same dye, as the MWCO of the composite membrane increased, the retention rate of dye decreased and the water permeability ascended. Meanwhile, it was found that Donnan effect had impact on separation of electriferous dyes. The retention rates of the composite UF membrane with MWCO1000 Da for Methylene blue, Rhodamine B, Methyl red, Congo red and Methyl blue were 30.8%, 68.1%, 78.9%, 97.3%, and 99.9%, respectively, while the retention rate of the inorganic salt NaCl was only less than 20%. The permeability of the membrane for the above five dyeing wastewater were 20.2, 23.3, 25.9, 25.1 and 24.9 l/m2·h·bar, respectively. Furthermore, the membranes with MWCO of about 1000 Da were also used to treat Congo red dyeing wastewater under different trans-membrane pressures, NaCl concentrations, operating times, cleaning agents, and concentrating rates. The results of dye removal experiments showed that thin-film composite UF membranes with MWCO of about 1000 Da could separate dyes Methyl blue and Congo red effectively from NaCl, and that the composite UF membranes with small pore size had good prospects in dyeing industry, especiall in the treatment of dyeing wastewater.