| Due to the outdoor air pollution and indoor personnel activities,indoor air pollution components are extremely complex and have senously jeopardized people's life and health.PM2.5 and microbes are important components,which have always been the focus of researchers.Electrospun nanofibers are widely used in high-efficiency filtration because of their simple preparation,large specific surface area,small pore size and good pore connectivity.In this paper,electrospinning technology was used to prepare surface-porous antibacterial micro/nanofibers using Poly(lactic acid)and chitosan nanopowder as raw materials.The effect of the properties of the spinning solution on the spinnability was investigated.The process parameters such as spinning voltage,solution flow rate,receiving distance,spinning solution concentration and ambient relative humidity were optimized.The effects of CS nanopowder content in the spirning solution on the morphology,structure and properties of the fibers were studied.The effects of the spinning time and the pore structure of the fiber surface on the filtration performance and air purification performance of the membrane were discussed.The results are as follows:(1)Preparation and properties of spinning solution:The CS nanopowder was uniformly dispersed in the PLA solution to obtain a spinning solution.With the CS nanopowder added into the PLA solution,the viscosity of the spinning solution increased and the electrical conductivity decreased;When the mass fraction of PLA/CS in the spinning solution increased(fixed ratio was 4/1),the viscosity of the spinning solution increased,and the conductivity decreased.YVhen the mass fraction of PLA was 8%,the mass fraction of CS nanopowder changing in the range of 1?2.5%had no significant effect on the viscosity of the spinning solution.(2)Optimization of spinning process parameters:When the spinning solution was PLA-8/CS-2 and under the condition of relative humidity of 45±3%,the three-factor four-level orthogonal test table was used to optimize the spinning process parameters(spinning voltage,solution flow rate and reeeiving distance).The minimum fiber diameter was used as the reference index.The optimized spinning process parameters were as follows:the spinning voltage was 18 kV,the flow rate of spinning solution was 1 ml/h and the receiving distance was 14 cm.When the spinning process was carried out under optimized conditions of spinning process with a relative humidity of 45±3%,as the concentration of the spinning solution increased,the beads in the fibers gradually decreased until disappeared,when the mass fraction of PLA and CS were 8%and 2%,respectively,the fibers were uniform and the surface was distributed with a large number of nanopores;when the spinning solution was PLA-8/CS-2,the higher the relative humidity of the environment was,the larger the fiber diameter was,and the pore width of the surface and the pore coverage both increased.When the relative humidity of the environment was 45%,the prepared nanofiber membrane had the best filtration efficiency.(3)Distribution of CS nanopowder on fibers:TEM and EDX results shown that a large number of CS nanoparticles were evenly distributed on the surface of PLA/CS micro/nanofibers prepared by dispersing CS nanopowder in PLA solution.(4)Effect of the content of CS nanopowder in the spinning solution on the morphology,structure and properties of the fibers:Adding CS nanopowder into the PLA solution,the diameter of the nanofiber,the width and coverage of the surface pores were significantly increased,the pore diameter of the fiber membrane increased,and the filtration efficiency and pressure drop decreased remarkably.As the mass fraction of CS nanopowder in the spinning solution increased,the fiber diameter and the width of the surface pore were less affected,and the pore coverage and the pore size of the through-pore showed an upward trend,the filtration efficiency of the fiber membrane gradually increased,and the pressure drop decreased.The filtration efficiency of the fiber membrane PLA-8/CS-2.5 reached 98.99%,while the pressure drop was only 147.60 Pa,and the quality factor was 0.0312,performing the best filtration efficiency.The higher the content of CS nanopowder in the fiber membrane,the higher the crystallinity of the PLA/CS nanofiber membrane was,and the better the bacteriostatic performance was.The inhibition rate of the nanofiber membrane PLA-8/CS-2.5 against Staphylococcus aureus was 99.5%,and against Escherichia coli was 99.4%,which had a good antibacterial property.(5)Effect of spinning time and pore structure on the air purification performance of fiber membrane:As the spinning time was prolonged,the amount of fiber deposition increased,the fiber membrane became thicker and the through-pore size decreased,the filtration efficiency becoming better and the air punfication performance was improved.The air purification property of PLA-8/CS-2.5-4h and PLA-8/CS-2.5-6h were better than that of the car air purifier.However,the pressure drop during filtration improved with the spinning time prolonged,hindering air circulation,so that the purification property of PLA-8/CS-2.5-6h was better than PLA-8/CS-2.5-8h.The optimal spinning time was 6h.The larger the relative humidity of the environment during spinning was,the larger the pore width of the fiber surface and the higher the coverage rate were.When the humidity was increased from 15%to 45%,the filtration efficiency was gradually improved and the air purification performance was significantly enhanced.However,when the humidity was too large,the fiber diameter was large,and the filtration performance and the air purification performance was deteriorated.The optimum relative humidity was 45%. |
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