Study On Preparation And Properties Of Polyethersulfone/Nanocellulose Ultrafiltration Support Layer And Composite Nanofiltration Membrane

The research of composite nanofiltration membrane began in the late 1980 s.As one of the core materials of membrane separation technology,it is an advanced separation membrane material with separation properties between ultrafiltration membrane and reverse osmosis membrane.The pore size of nanofiltration membrane is about 1 nm.Besides,the ability to selectively separate ions of different valence states lead to the widely used in the fields of brine denitration,pharmaceutical,chlor-alkali,food and beverage.The commercial composite nanofiltration membrane is mainly composed of a non-woven fabric,a polysulfone ultrafiltration support layer and a piperazine-based desalting layer.In practical applications such as denitrification of brine,a series of problems such as supporting lamination and de-salting layer contamination are often encountered,which greatly reduces the operating efficiency and time of the membrane system.Therefore,the development of a new ultrafiltration support layer which has stronger mechanical strength and anti-pollution ability than the conventional polysulfone support layer is particularly important.Compared with the traditional support material polysulfone,polyethersulfone has higher hydrophilicity,acid and alkali resistance and pore structure controllability,so it has been successfully applied to the development of ultrafiltration membranes with precise molecular weight cutoff.At the same time,considering that nanocrystalline cellulose has high chemical stability,polyhydroxy characteristics,environmental friendliness and strong water dispersion ability,a new high-strength ultrafiltration support layer was prepared by using polyethersulfone doped nanocrystalline cellulose,and the effect of nanocrystalline cellulose content on the structural properties of ultrafiltration membrane was studied in this paper.On this basis,combined with interfacial polymerization technology to prepare composite nanofiltration membrane with high pressure tightness and anti-pollution ability,the effects of interfacial polymerization factors on the structure and separation performance of composite nanofiltration membrane were systematically studied.In this paper,nanocrystalline cellulose was prepared by hydrolysis of microcrystalline cellulose by sulfuric acid,and the prepared nanocrystalline cellulose was characterized by FT-IR and AFM.The results show that nanocrystalline cellulose has been successfully prepared and its basic chemical structure has not changed.A series of polyethersulfone/nanocrystalline cellulose composite ultrafiltration membranes with different nanocrystalline cellulose content were prepared by immersion precipitation phase transformation method.We analyzed the changes of chemical structure,hydrophilicity,surface potential,mechanical strength and anti-pollution performance of composite ultrafiltration membrane by FT-IR,SEM,AFM,contact angle measuring instrument and potentiometric titrator.The results show that nanocrystalline cellulose enhanced some properties of the composite ultrafiltration membrane,such as hydrophilicity,the surface electronegativity,the tensile strength of the cortex,the anti-pollution performance,the porosity and the pure water flux.When the content of nanocrystalline cellulose was 0.50%,the water contact angle of the composite ultrafiltration membrane was 57.1°,which was 22.94% lower than the polyethersulfone ultrafiltration membrane;the tensile strength of the composite ultrafiltration membrane was 4.01 MPa,which was increased by 78.22% compared with polyethersulfone ultrafiltration membrane;composite ultrafiltration membrane porosity reached a maximum of 85.70%,which was increased by 15.19% compared with polyethersulfone ultrafiltration membrane porosity;The water flux of the composite ultrafiltration membrane reached a maximum of 714.33 GFD,which was increased by 29.67% compared with polyethersulfone ultrafiltration membrane.Subsequently,we selected a polyethersulfone/nanocrocrystalline cellulose composite ultrafiltration membrane with an optimum content of 0.50% of nanocrystalline cellulose as the base film,and prepared a composite nanofiltration membrane by interfacial polymerization.The results show that the piperazine mass fraction was 3%,the trimesoyl chloride mass fraction was 0.15%,and the interfacial polymerization time was 20 s,which was the optimal condition for interfacial polymerization.The composite nanofiltration membrane prepared under these conditions had improved pressure tightness and anti-pollution ability compared with the commercial composite nanofiltration membrane.In summary,the use of nanocrystalline cellulose and polyethersulfone for blending treatment could improve the hydrophilicity,mechanical strength,anti-pollution performance and filtration performance of the ultrafiltration support layer of the composite nanofiltration membrane.At the same time,the polyethersulfone/nanocrocrystalline cellulose composite ultrafiltration membrane was used as the base membrane,and the composite nanofiltration membrane prepared by the interfacial polymerization method had better resistance to compaction and pollution resistance than the commercial composite nanofiltration membrane.