Studies On PDMAEMA/PSF Positively Charged Composite Nanofiltration Membrane

In this paper, a positively charged composite nanofiltration membrane was developed by using poly(N,N-dirnethylaminoethyl methacrylate) (PDMAEMA) as the active layer material and polysulfone (PSF) macrofiltration membrane as the support layer. The developing technique and characteristic of the active layer material and the nanofiltration membrane were studied.PDMAEMA was prepared by free radical bulk polymerization using AIBN as the initiator. The polymer can be purification by hollow fiber ultrafiltration and this method can efficiently remove small molecules in the system.PDMAEMA can be cross-linked by quaternization to develop a positively charged dense network structure. According this mechanism, PDMAEMA/PSF positively charged nanofiltration membrane was developed by interfacial polymerization using PSF plate macrofiltration membrane as support layer, pre-polymer of PDMAEMA water solution as coating solution, p-xylylene dichloride/heptane as cross-linking agent. Technique and condition of developing membrane such as thickness of support layer, concentration of coating solution, coating time, pH value of coating solution, concentration of small molecular additive in coating solution, concentration of cross-linking agent, cross-linking time and composite times were studied. FTIR, SEM and XPS were employed to characterize the structure of membrane. The investigation showed that nanofiltration membrane with good character can be made when concentration of coating solution is 1%-2%, coating time is 1 hour, concentration of cross-linking agent is 0.5% and cross-linking time is 5 hours.This membrane has rejection to inorganic salt in water solution and the rejection ratioto higher value inorganic ions (RMg2+-90%) is greater than the rejection ratio to lower value inorganic ions (RNa+-70%). The rejection ratio of this membrane to inorganic salts is ordered: MgCl2>MgSO4>NaCl>Na2SO4. The water flux is about 10-20L/m2h (0.8MPa, 30 C, MgSOlg/L). The membrane exhibits a response behavior for pH value of solution: when the membrane in a neutral solution, it possesses a higher water flux and rejection ratio; when the membrane in a solution with upper or lower pH value, it possesses a lower water flux and rejection ratio. The membrane has resistance to oxidation medium or free chlorine. The results of study also showed that this membrane should be keep in antiseptic.