Study On Preparation And Properties Of PA/PI Solvent Resistant Composite Nanofiltration Membrane

Solvent resistant nanofiltration?SRNF?membrane is of great importance for the nanofiltration process to expand from water system to organic solvent system.Compared with asymmetric membrane,the composite nanofiltration membrane based on solvent-resistant materials and prepared by interfacial polymerization has better comprehensive performance.Polyimide?PI?have excellent chemical stability,and soluble PI is an excellent film making material.Therefore,this article explores the optimization conditions of the soluble PI synthesis process and provides a reliable basis for the selection of PI process parameters for industrial production.Based on this,PA/PI composite nanofiltration membranes were prepared by interfacial polymerization.Diamines with carbonyl-containing dianhydrides and short-chain alkyl side groups in the molecule are selected as the reaction monomers,and a prepolymer-polyamic acid?PAA?is synthesized by low-temperature polycondensation reaction,and chemically imidized to prepare soluble PI.The structures and properties of PAA and PI were characterized by means of FT-IR,¹HNMR,TG,GPC,DSC and XRD.The results show that PAA was successfully synthesized and completely imidization to obtain a high content PI.The molecular weight of PI was 300000,it is an amorphous structure polymer.The glass transition temperature is 300?.Under N₂atmosphere,the temperature at 5%weight loss is 510°C,and the heat resistance is better than PAA.The synthesized PAA and PI have good solubility in organic solvents such as NMP,CHCl3 and THF at room temperature.The PI substrate was prepared by phase inversion process and modified by chemical crosslinking.The effects of crosslinking agent concentration and crosslinking time on the solvent resistance and surface properties of the base film were investigated The positive charge on the surface of the membrane increases,and the decrease in the molecular weight cut-off?MWCO?of the PI-based membrane after cross-linking is measured.PA/PI composite nanofiltration membranes were prepared by interfacial polymerization on cross-linked PI substrates.The effects of PIP concentration,TMC concentration,interfacial polymerization time and heat treatment time on the separation performance of the composite membrane were investigated.The structure and morphology of the composite membrane were characterized by FT-IR,XPS,SEM and AFM,and the MWCO of the composite nanofiltration membrane was 400 g/mol under the optimum technological conditions.The comprehensive performance test was carried out on the optimized composite nanofiltration membrane,including the separation performance of two different dyes and the solvent resistance.The results show that the composite nanofiltration membrane has better separation performance.After soaking in several common organic solvents such as methanol,isopropanol,acetone,ethyl acetate,n-hexane and DMF for 15 days,The separation performance of Brilliant Blue?Mw=840 g/mol?remained unchanged,indicating that the composite nanofiltration membrane has high solvent resistance.