Preparation And Proerties Research Of Nanocellulose Nanofiltration Membranes

Nanocellulose,as a kind of renewable and sustainable organic nanomaterials,has good mechanical property,the easily functionally modified surface,high specific surface area and other several excellent properties.It has been studied in a wide range of application,such as enhancing the composites,food packing,nanopaper,biomedicine and so on.In recent years,nanocellulose has been paid more attention in membrane separation of water treatment because of its strong hydrophilicity and the ability of forming fiber network structure.In addition,with the requirements of "full life cycle" for the industrial products,nanocellulose is expected to become a new development direction of membrane materials.The nanocellulose membranes prepared by filtration method were only applied in microfiltration or ultrafiltration process to remove bacteria,viruses or separate oil and water.It’s difficult for these membranes to play an effective role in fine separation,so the research on preparation of new composite nanofiltration membranes with nanocellulose as the key material is expected to expand its application in membrane separation.Carboxymethylated cellulose nanofibers(CNF)were used as the raw material in this paper.Firstly,nanocellulose membrane was prepared by vacuum filtration method with polyacrylonitrile(PAN)ultrafiltration(UF)membrane as the support layer.In order to improve its separation performance and poor stability,CNF were blended with carbon nanotubes(MWCNTs)and graphene oxides(GO)respectively to prepare nanocellulose and carbon nanomaterials mixed matrix nanofiltration membranes.Secondly,in order to prepare new composite membrane with nanocellulose as the single material of separation layer,nanocellulose nanofiltration membranes were prepared by coating method.This section also investigated the effects of the combinability between CNF water dispersion and polysulfone(PSf)UF membrane and the effects of glutaraldehyde as cross-linking agent on the membrane performance.Finally,nanocellulose/carbon nanomaterials mixed matrix membranes were prepared by coating method with MWCNTs and GO as the dispersion phase respectively.The effects caused by the addition of carbon nanomaterials on CNF aggregation morphology and membrane performance were also investigated.Specific content and conclusions are as follows:(1)Nanocellulose nanofiltration membrane was prepared by vacuum suction filtration.The results showed that the rejection of Na2SO4 was only 67.4%when the nanocellulose mass was 0.2mg and the membrane area was 12.56cm2,and after running or soaked in water for a long time,the separation layer was easy to swell or even fall off.(2)In order to improve the performance of nanocellulose nanofiltration membrane prepared by vacuum suction filtration,CNF were blended with MWCNTs and GO respectively and nanocellulose/carbon nanomaterials mixed matrix nanofiltration membranes were prepared.The results showed that with the addition of carbon nanomaterials,the morphology and surface properties of membranes showed the intrinsic properties of carbon nanomaterials.When the mass ratio of MWCNTs and CNF was 1,the separation performance of membrane was optimized and the rejection of Na2SO4 is 71.2%.When the mass ratio of GO and CNF was 0.5,the separation performance of membrane was optimized and the rejection of Na2SO4 was 80.7%.(3)Nanocellulose nanofiltration membranes were prepared by coating method after acid treatment of CNF dispersion.The results showed that pH was the main factor affecting the combinability between CNF water dispersion and PSf UF membrane and the membranes crosslinked with glutaraldehyde showed better salt-cut performance and stability.When the CNF concentration was 0.5wt.%,the rejection order of four inorganic salt ions was Na2SO4,NaCl,MgSO4 and MgCl2 according to the sort order of size and the rejection of orange G and Congo red was more than 95%,indicating that the composite membranes had a certain application potential in salt separation and interception of small molecule pollutants.(4)MWCNTs and GO were incorporated into the crosslinked CNF nanofiltration membranes and nanocellulose/carbon nanomaterials mixed matrix membranes were prepared by coating method.The results showed that the addition of MWCNTs resulted in a little phase separation with CNF,resulting in additional molecular channels,which increased the flux and decreased the rejection slightly.The addition of GO not significantly altered the aggregation morphology of CNF,and couldn’t form effective molecular channels in the membrane,and because of its dense non-porous lamellar structure,the water molecules transferring was blocked in the vertical direction,which decreased the flux and had no effect on the rejection.In this paper,composite nanofiltration membranes with nanocellulose as the key material were prepared by vacuum suction filtration and coating method respectively and the separation properties of these membranes were investigated.The two methods of membrane preparation in this paper are simple and easy to realize industrial production.It provides a new method and idea for the preparation of nanocellulose nanofiltration membrane,and extends the application of nanocellulose in water treatment.