Relationship Between Formation And Arrangement Of Electrospun Fibers And Performance And Structure Of Membranes

In this thesis,PSU composite nanofiber membranes were produced by dissolving PSU particles in a mixed solution of DMF and acetone and adding SiO2 particles with different diameters or blending with polyamide 6 through multi-jet electrospinning.The structure,pore size and porosity,permeability,mechanical properties and filtration performance of composite nanofiber membranes with various structures were investigated.Finally,the PSU composite membrane with the best filtration performance was obtained by comparing the quality factor of the composite membranes with various structures.Structure and performance of thick/thin composite membranes:PSU nanofibers with different diameters were fabricated by adjusting the concentration of spinning solution through parallel multi-jet electrospinning.As a result,the proportion of fine-diameter fibers of four prepared membranes:PSU-18>PSU-18-22>PSU-22-18>PSU-22.The permeability,mechanical property,pore size and porosity of thick/thin composed nanofiber membranes were in the middle of PSU-18 and PSU-22.Furthermore,PSU-18 has the highest filtration efficiency and pressure drop and PSU-22 has the lowest,while thick/thin composed nanofiber membrane has higher than 99%filtration efficiency and lower pressure drop.After calculation,the quality factors of PSU-18,PSU-18-22,PSU-22-18 and PSU-22 membranes are 0.0066,0.0067,0.0069 and 0.0061 respectively.Therefore the filtration performance of thick/thin composite membrane is superior to the PSU membrane with single diameter.Structure and performance of PSU/SiO2 composite membranes:In order to further improve the filtration performance of the PSU membrane,SiO2 microspheres with the diameter of 300nm and 900nm were added to the spinning solution to adjust the pore structure of the membrane.The results show that as the mass percentage of the microspheres increased,the mechanical property and filtration performance of the composite membrane firstly reduced and then gradually increased,while the pore size,porosity and permeability firstly increased and then reduced.The pore size,porosity and permeability are higher than PSU membrane,while the mechanical property and filtration performance are lower than PSU membrane when the ratio between thick and thin fiber is 2:1 and the mass percentage of the microspheres is 4%.As the thickness of composite membrane increased,the quality factor of the membrane firstly decreased and then increased.The quality factor of the PSU-900 SiO2 composite membrane is 0.0086,which was significantly lower than the quality factor of the PSU-300 SiO2 composite membrane(0.0128)in the condition of same mass percentage of microspheres.The quality factor of the three-component composite membrane is 0.0079,which was significantly lower than the quality factor of the PSU-300 SiO2 composite membrane in the condition of same thickness.Therefore PSU-300 SiO2 composite membrane has better improvement effect on the filtration performance.Structure and performance of PSU/polyamide 6 composite membranes:As the thickness of polyamide 6 nanofiber layer increased,the pore size and permeability of the composite membrane reduced,the porosity and mechanical property were substantially constant,the filtration efficiency improved,while the pressure drop also increased.The quality factor of PSU composite membrane added 1h spinning time polyamide 6 nanofibers is 0.0181,which has the best filtration performance.In conclusion,PSU-300 SiO2 composite membrane with 5%mass percentage of microspheres has the best improvement effect on the filtration performance of PSU membrane comparing to the other two kinds of composite membranes.