Preparation And Performances Of PVC Hollow Fiber Membranes

Abstract: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 chloride)(PVC) is one of the highest productions of synthetic resin, has a wealth of sources, with a stable chemical property and high strength. PVC is an attractive membrane material.Poly (vinyl chloride)(PVC) hollow fiber membranes were prepared via non-solvent induced phase separation (NIPS), with dimethylacetamide (DMAc) as diluent. It is found that PVC hollow fiber membranes present finger-like structure and sponge-like structure, small pores at inner surface and relatively dense outer surface. It is found that with bore liquid flow rate increasing from0.074to0.209g/s, the layer of sponge-like decreases, the finger-like pore and the thickness of dense outer surface enlarged, the wall thickness decreases from0.35mm to0.16mm, which leads to water flux increasing from0.44×10-7m3·(m2·s·kPa)-1to3.69×10-7m3·(m2·s·kPa)-1and the improve of reection ratio and tensile strength decreasing from6.57MPa to5.84MPa, elongation decreasing from5.33%to4.9%, With air gap increasing from1cm to9cm, the thickness of the dense layer near the outer surface increases, which leads the improve of rejection ratio and water flux decreasing from9.01×10-7m3·(m2·s·kPa)-1to2.08×10-7m3·(m2·s·kPa)-1, the improve of inner surface pores and the existence of finger-like structures lead to tensile strength decreasing from11.8MPa to6.61MPa, elongation decreasing from10.3%to8.2%. The electrokinetic phenomena of self-made PVC hollow fiber membrane modules were investigated. The results show that the module has 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. It is found the the isoelectric point of the module in different electrolytes. It is around2.8in monovalent media (NaCl and KCl); divalent electrolytes (CuCl2and CaCl2) have an IEP significantly higher, it is equal to3.1.In order to improve the hydrophilicity of PVC, PVC is blending modified by cellulose acetate (CA) polymer. The compatibility of PVC/CA blending polymers was investigated by theoretical and experimental methods:heat of mixing and dilute solution viscosity (DSV) method. The method of heat of mixing reveals that the PVC/CA blending system is full compatible. DSV method reveals the compatibility is favorable affecting by blending ratio, concentration and temperture. Then PVC/CA blend hollow fiber membranes were prepared by NIPS, it is found that the membrane has finger-like structure, dense layer, and inner surface with small pores. With the increase of CA concentration, sponge-like structure is nearly disappeared, the pore size of finger-like structure and thickness of outer surface is enlarged, which lead to the increase of water flux and decline of mechnial properties.