Study On Preparation Of PVA/PEI/β-CD Composite Nanofiltration Membrane And Its Performance

With the developing of membrane technology,the research of polymer composite membrane play important part.The preparation of nanofiltration membrane is mainly used composite nanofiltration membrane technology.Compared with the traditional homogeneous membrane,composite membrane has better separation performance,mechanical and chemical stability,etc.This paper intends to combineβ-cyclodextrin（β-CD）which has good hydrophilicity and cavity structure with polyelectrolyte（PEI）which has strong hydrophilicity,good chemical stability and positively charged and polyvinyl alcohol（PVA）has good solvent resistance,mechanical properties and advantages of membranous,to prepare PEI/PVA/βCD composite nanofiltration membrane which has good separation performance and chemical stability.The technologies of coating and crosslinking were first introduced in the experimental process.In this paper,the polycationic polyethyleneimine（PEI）as a cationic additive is blended with polyvinyl alcohol（PVA）to prepare positively charged composite nanofiltration membrane with polysulfone ultrafiltration membrane as supporting layer.The impact of membrane preparation conditions on membrane performance was discussed.The chemical composition,surface morphology and hydrophilic of the film were characterized by infrared spectroscopy,scanning electron microscopy and the contact angle.Under the condition,addβ-CD in the PVA/PEI composite membrane to improve flux.Then using PEI/PVA/β-CD composite nanofiltration membrane to separate different inorganic salts,and the effects of operation conditions on the composite membrane separation.Get the following conclusion:Microstructure characterization of composite membrane indicates that PVA and PEI blend membrane crosslinked with glutaraldehyde can successfully make composite layer on the polysulfone（PS）ultrafiltration membrane.The isoelectric point of membrane move to the alkaline direction,and composite membrane surface is positively electric property in the scope of the neutral and acidic,and with the decrease of the pH,electropositive of composite membrane gradually enhanced,because there are many aminos in the polymer molecular chain.The performance of PVA/PEI composite membrane affected by preparation parameters,such as concentration of crosslinking agent,heat treatment time and temperature,PVA content and the PEI content.The increase of crosslinking agent concentration and heat treatment temperature can accelerate the crosslinking reaction of PVA.Due to the improvement of the density of composite membrane surface,and increase of the rate of interception in composite membrane,lower the permeation flux of the membrane decline.With the increase of concentration of PEI,the hydrophilic and flux of the membrane rise,but when the concentration of PEI is more than 8:1,the rejection rate declines.The results show that the optimum polymerization condition are as follows:the concentration（mass fraction）of PVA and PEI are 2%,PVA:PEI=8:1,the concentration of glutaraldehyde is 2%,the concentration of sulfuric acid is 1%,dried temperature is 70℃.The membrane prepared under the optimum conditions exhibited a rejection of 94.52%to 2 g/L MgSO₄ with flux of 5.91 L/（m²·h）.With the increase ofβ-CD content,the flux of composite membrane increases significantly,and the separation performance shows that the intercept molecular weight of PEI/PVA/β-CD composite nanofiltration membrane is 1420 Da.A salt rejection order of MgSO₄>MgCl₂>Na₂SO₄>NaCl,which shows the typical load characteristics for the separation of positively charged nanofiltration membrane.Modification of PVA composite nanofiltration membrane has better performance and higher flux.