Preparation And Characterization Of Poly(Vinyl Butyral)(PVB) Hollow Fiber Membrane

Membrane separation technology shows a great application prospect because of its high efficiency, energy saving, high flexibility and process capability. The properties of membrane materials are important in the application of the membrane. Poly(vinyl butyral)(PVB) is a product of the reaction between poly(vinyl alcohol)(PVA) and butyl aldehyde in the presence of an acid catalyst. Being an excellent membrane forming polymer, PVB can endure the low temperature, light, and change in humidity, bacteria, microorganism, alkali and diluent acid. Moreover, Poly(vinyl butyral)(PVB) is an attractive hydrophilic membrane material because its hydroxyl groups can provide with some hydrophilicity.Thermally induced phase separation (TIPS) process has become a promising and vitality membrane preparation method because it has some advantages over the conventional membrane preparation methods, such as low tendency for defect formation, and effective control of the final pore size. Poly (vinyl butyral)(PVB) hollow fiber membranes were prepared via thermally induced phase separation, with polyethylene glycol (PEG) as diluent. It is found that PVB hollow fiber membranes prepared via spinodal decomposition present a quite asymmetry interconnected sponge-like structure:larger pores at inner surface and relatively smaller pores at outer surface. The formation of larger pores at inner surface is due to the replacement of the rich diluent phase formed near the inner surface via liquid-liquid phase separation. The reason for the dense layer near the outer surface is that the increase of the polymer concentration because of the evaporation of diluent at the outer surface. It is found that with air gap increase from0cm to3cm, the thickness of the dense layer near the outer surface increases, which leads the improve of retention rate and mechanical properties, but a reduction of water flux. With increase of extrusion temperature from140℃to170℃, the pore size of the inner surface decreases, but the thickness of the dense layer near the outer surface increases, which cause the water flux decreased, but the rejection and mechanical properties of the membrane significantly increased. Moreover, the addition of F127in the casting solution can effectively improve the permeability of PVB hollow fiber membrane.The electrokinetic phenomena for two self-made PVB hollow fiber membrane modules (M40and M200) with different pore size were investigated. The results show that modules M40and M200have a weak negative charge due to the specific adsorption of anions. Compared with anions, the cations have significant influence on the the electrical properties of the membrane. The absolute value of streaming potential and zeta potential decreased with increasing salt concentration. The larger the membrane pore size, the greater the absolute value of the streaming potential and the zeta potential. The results show that M40and M200have the same isoelectric points when studied in the same cation valence solutions:it is around3.0in monovalent media (NaCl and KCl); divalent electrolytes (CaCl2and MgCl2) have an IEP significantly higher, it is equal to3.5. The observed salt retentions for M40and M200can be explained by the negative charge of membrane surface, which rejected inorganic solutes by means of electrostatic repulsion effect even though membrane pore size is much larger than the salt size.