Preparation Of Uv Graft Hydrophilic Nanofiltration Membrane

Nanofiltration (NF), a pressure-driven separation process, has various applications in many fields, especially in water treatments and the separation of low molecular weight organic compounds. Because of its advantages such as low operating pressures, high fluxes, high retentions of multivalent salts, low investment and operation costs, this technology has rapidly developed in the last ten years. The new applications of nanofiltration in the fields of biotechnology and pharmacy, where the fluid phases to be treated are generally complex and heavily loaded with colloidal matters, require hydrophilic membranes with better fouling resistances.In this article, a novel method was used to prepare hydrophilic nanofiltration membrane by UV irradiation graft polymerization from Polyetherketone (PEK-C) ultrafiltration membrane. The grafting condition and effect of monomer nature on the membrane performance such as salt rejection and permeate flux have been systematically studied. By introducing chain transfer agent and other polar monomer in the grafting solution, the surface nature and structure of the membrane have been changed. The results showed that the function of Donnan effect on the membrane performance, which are very helpful to understand the mechanism of nanofiltration.We introduced at first the graft polymerization of PEK-C ultrafiltration membrane by hydrophilic monomer such as acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) in presence of benzophenone BP as photosensitive agent. Several analytic methods such as FTIR-ATR, AFM, CAs were employed to characterize the chemical and physical properties of modified membranes. FTIR-ATR spectra detected AA and HEMA grafts on the surface of PEK-C, and the relative grafting ratio increased with irradiation time, while the contact angle of water on the modified membrane surface measured by CAs decreased. That means the hydrophilicity can be improved by hydrophilic monomers grafting onto the surface of PEK-C membranes. The modified PEK-C membrane showed a good retention to salt that is a characteristic of nanofiltration. The difference in separation performance of membrane modified by AA or HEMA under the similar grafting condition demonstrated that the membrane negatively charged has a higher salt retention. For example, the retentions to sodium sulfate of the membrane grafted AA and HEMA for 90 min under UV intensity of 1.6 mW/cm~2 was 94.1 % and 39.5 % at 0.4 MPa, respectively.The UV irradiation graft polymesization of PEK-C membrane has been also studied in the absence of photoinitiator. The analysis with FTIR, CAs and AFM detected that the graft polymerization took place as well as in the presence of BP too. It showed that the PEK-C is aphotosensitive polymer. According to its chemical formula, we suggested that the structure of benzophenone in main chain of PEK-C could be the photosensitive center. In presence of hydrogen-donor, under UV irradiation, benzophenone would transfer to pinacol radical, and initiated the graft polymerization.The effect of irradiation condition and monomer nature on the membrane performances of modified membrane was systematically investigated. The results obtained by means of FT1R-ATR, AFM, CAs showed that the irradiation graft polymerization of hydrophilic monomer on the PEK-C UF membrane in the absence of BP followed the similar trend that the grafting degree on the membrane surface and their hydrophilicity increased with increasing in irradiation intensity or irradiation time. The retention of sodium sulfate of the membrane modified with 10% of acrylic acid for 5 min irradiation with a UV intensity of 8.7 mW/cnr was very high, about 99.6 % at 0.8 MPa. This result suggested that part of AA chains grafted on the micro-porous wall and decrease the pore sizes on the nanometer order under suitable irradiation condition within a few minutes. According to the experiment results, we discussed the membrane forming process and the mechanism of nanofiltration separation based on extended Nernst-Planck equation. It suggests that the rejection of a charged solute depends on the steric exclusion from partially occluded by grafted PAA chains in the membrane pores and the static expulsion by Donnan potential of PAA chains. It means that the membranes performance can be controlled with varying the length of grafting chain, the grafting ratio and their electronegative properties.UV direct irradiation grafting and polymerization and the nanofiltration performance of four different hydrophilic grafted monomers [neutral (acrylamide (AM), weak acid (2-hydroxyethyl methacrylate (HEMA), acrylic acid (AA), and strong acid (2-acrylamido-2-l-propanesulfonic acid (AMPS)) on PEK-C membranes were measured. Although all the grafted and polymerized monomers increased the surface hydrophilicity of the PEK-C grafted membrane over that for the unmodified PEK-C membranes, their effect on nanofiltration performance was quite different. Using the PEK-C membranes for grafting, membrane with superior performance (high salt retention, high salt solution flux) was obtained with the AMPS. Grafting of AM resulted in substantial decrease in permeability due to the membrane pores were largely occlude by PAM chains, but their retention to salt were very low, even at high AM graft ratio. Those results also testified that more electronegativity of the monomer is, the better nanofiltration performance of the modified membrane. The use of chain transfer agent, iso-propane alcohol (1PA) was use in producing hydrophilic...