Study On The Regulation Mechanism Of Macromolecular Water-phase Additives On The Structure Of Polyamide Composite Membranes

Nanofiltration membrane technology has become more and more widely used in today's industrial development.Interfacial polymerization(IP)is currently one of the most commonly used methods for preparing nanofiltration composite membranes.The addition of different additives to the aqueous phase in the interfacial polymerization process can have different effects on the surface structure of the membrane.However,there is a lack of correlation between physical and chemical properties of additives and the structure of the membrane.Therefore,it is important to study how aqueous phase additives affect the structure of polyamide nanofiltration membranes to prepare high-performance composite nanofiltration membranes.In this subject,The optimized membrane forming conditions were obainted by varying the interfacial polymerization condition.The main research conclusions are as follows:when the content of polysulfone is constant,and the water fluxes of the porous substrate prepared with three different solvents of dimethyl formamide(DMF),dimethyl acetamide(DMAc)and N-methylpyrrolidone(NMP)are 172.857,178.337and 37.13 L/(m~2·h),respectively.The best salt rejection is 60.73±3.93%,so DMF is selected as the solvent for porous substrate preparation;when other conditions are constant,12,15 and 20 wt%of polysulfone are added to prepare the porous substrate.The water fluxes of the membrane are 288,331.53 and 91.04 L/(m~2·h).The porous substrate with 15 wt%polysulfone content has the best performance,and the salt rejection rate is 75.23%;when other conditions are constant,2,3 and 4 wt%of polyvinylpyrrolidone were added to prepare the porous substrate,and 3 wt%is best.Then,under certain porous substrate conditions,the nanofiltration composite membrane is prepared by interfacial polymerization,and PVA 1788?PVA 1799?polyethylene glycol PEG 10000 and PVP K15 are selected as aqueous phase additives.The membranes are prepared by interfacial polymerization(IP)of m-phenylene diamine(MPD)orpiperazine(PZ)in the aqueous phase and trimesoyl chloride(TMC)in the organic phase on the surface of a polysulfone substrate.Then,they are used to explore the mechanism of the influence of aqueous-phase additives on the membrane structure.The surface structure and surface roughness of the film formed under different conditions were compared by atomic force microscope(AFM).In addition,UV spectrophotometer,gas chromatography,viscosity test and other characterization methods were used to determine the presence of polyvinyl alcohol.The particle size distribution,diffusion tendency and viscosity properties of the aqueous phase solution under the following conditions were characterized,and the relevant physical and chemical properties of the aqueous phase solution were explored.In this study,it is confirmed that the solubility and dispersion of macromolecular additives in the aqueous solution and the degree of polymerization reaction will all affect the structure of the composite membrane.This work provides a new design idea for the further understanding of the preparation of polyamide nanofiltration membranes.