Preparation And Modification Of CA Nanofiber Membrane And Application In Oil/Water Separation

In recent years,frequent crude oil spill accidents with the oil development and transportation of offshore oil as well as the oil pollution caused by the development of chemical industry,textile mills and food industry have become one of the most pressing environmental issues in the world.Therefore,the separation of immiscible liquids represented by oil/water separation has received widespread attention from the academic community.Electrospinning technique is one of the most effective methods for preparing nanofiber membranes.The prepared nanofiber membranes have the advantages of larger specific surface area,higher porosity,good connectivity,which makes they have wide potential applications in the field of oil/water separation.In this paper,cellulose acetate(CA)nanofiber membranes are prepared by electrospinning technique,and then modified by physicochemical methods.The influences of preparation process and modification methods on the morphology,structure,composition,porosity,hydrophilic performance,mechanical properties and oil/water separation performance of nanofiber membranes were studied.The main contents include as following:1.CA nanofiber membrane was prepared by electrospinning technique.The effects of electrospinning solution concentration,electrospinning voltage,collection distance and injection rate on the morphology,porosity and water content of CA nanofiber membranes were studied.The results showed that when the CA electrospinning solution concentration,electrospinning voltage,collection distance,injection rate,environmental temperature and humidity were 17%,18 k V,15 cm,1m L/h,25°C and 40%,respectively,the CA nanofiber membrane showed smooth surface and uniform diameter distribution.CA nanofiber membranes with different morphologies have certain differences in porosity and water content.Among them,the CA nanofiber membranes with bead structure have the smallest porosity and water content,indicating that the highest hydrophobicity.CA nanofiber membranes with smooth nanofibers and uniform diameter distribution have the worst hydrophobicity.Therefore,the porosity and water content of the CA nanofiber membrane can be adjusted by simply adjusting the morphology of the nanofiber membranes.2.CA nanofiber membrane was prepared by electrospinning technique,and then d-CA nanofiber membrane was obtained by the deacetylation method.The effects of deacetylation time on the wetting performance,self-cleaning performance,oil/water separation performance and corrosion resistance of d-CA nanofiber membranes were studied.The results showed that the wetting performance of the d-CA nanofiber membrane in air and liquid(water or oil)changes with the increasing of deacetylation time.Therefore,in order to meet different requirements for oil/water separation,the wettability properties of the CA nanofiber membrane could be easily controlled by simply adjusting the deacetylation time.The prepared d-CA/3 h nanofiber membrane has the characteristics of super-amphiphilic(super-hydrophilic and oleophilic)in air,super-oleophobicity under water and super-hydrophilicity under oil solely under the driving force of gravity,resulting in d-CA nanofiber membranes can be used as water-removing and oil-removing substances for oil/water mixtures.The d-CA/3 h nanofiber membrane can separate a pure oil/water mixture and an emulsified oil/water system,even in harsh environments such as those with strong acidity,alkalinity,or brine conditions,solely under the driving force of gravity.The d-CA/3 h nanofiber membrane also has high separation flux,high separation efficiency,simple preparation process,and good chemical stability.Besides,d-CA/3 h nanofiber membrane has super-hydrophilic properties under oil,which makes it show strong anti-pollution and excellent self-cleaning performance,avoid secondary pollution and have good reusability.3.To further enhance the mechanical properties of the d-CA nanofiber membrane,CA/TPU composite nanofiber membrane was prepared by electrospinning technique using CA and thermoplastic polyurethane(TPU)as raw materials,and then d-CA/TPU/3 h was prepared by deacetylation treatment.the influence of CA/TPU mass ratio on morphology,structure composition,surface wetting performance,mechanical properties,oil/water separation performance and corrosion resistance of composite membrances were studied by SEM,FTIR,XPS,contact angle test,universal tensile test,oil/water separation test.The results showed that compared with the d-CA/3h nanofiber membrane,d-CA/TPU/3h composite nanofiber membrane showed excellent mechanical properties and durability.It still maintain a rebound rate of more than 95%after cyclically stretched 10 times in a dynamic environment with a strain of 30%.Similarly,d-CA/TPU/3h nanofiber membrane can effectively separate a series of oil/water mixtures solely under the driving force of gravity.The highest water and oil removal fluxes reached up to 37,000 L/m~2·h and 74,000 L/m~2·h,respectively,separation efficiency is above 99%.Besides,the d-CA/TPU/3h composite nanofiber membrane has excellent anti-pollution performance and self-cleaning performance,therefore it does not have the problem of secondary pollution,and showed excellent reusability performance.