Study On Preparation And Properties Of Multifunctional High Temperature Resistant Air Filter Materials By Electrospinning

With the rapid development of modern industry and transportation industry,a large number of improperly treated high-temperature exhaust gases are discharged into the atmospheric environment.These high-temperature exhaust gases contain a large number of complex pollutants such as solid particles and toxic gases,which will not only seriously pollute the ecological environment,but also cause irreversible damage to the human respiratory system.In order to reduce the i MPact of pollutants on the environment and human beings,it is one of the most simple and effective methods to remove pollutants from the pollution source.High temperature waste gas is often filtered by"cooling before dedusting",and the temperature of the waste gas after cooling is still as high as 200℃.Therefore,high temperature resistant air filtering materials with excellent performance have become the key materials to remove solid particles from high temperature pollution sources.Traditional high temperature resistant air filter materials are mostly composed of metal and inorganic materials,which have the defects of easy oxidation,corrosion and poor wear resistance.Polyimide（PI）is a high-performance fiber material with high conjugate structure,which has the advantages of high strength,high modulus,heat resistance and corrosion resistance.It is an ideal matrix material for preparing high temperature resistant air filter materials.Electrospinning is a popular technology for preparing nano fiber materials.The nano fiber membrane prepared by this technology has a three-dimensional cavity structure with high porosity,which can achieve high filtration efficiency of the membrane.However,the PI nano fiber membrane prepared by this technology is difficult to achieve low pressure drop due to its ultra dense structure.Therefore,this topic takes PAA solution as raw material,uses electrostatic spinning and thermal amination process to build high temperature resistant air filter material with high efficiency and low resistance,and explores its adsorption performance for a variety of pollutants.Firstly,PI nanofiber membranes with different fiber morphologies were prepared by regulating the concentration of PAA polymer solution,combining electrospinning and thermal amination processes,and the effects of PAA solution concentration on fiber morphology,mechanics,thermodynamics and filtration performance were investigated.The results show that when the concentration of PAA solution is 18wt%,the PI nanofiber membrane has the best fiber morphology,its breaking strength and elongation are 10.533 MPa and 22.7%respectively,the filtering efficiency is 99.784%,the pressure drop is 211.68Pa,the filtering resistance is large,and the quality factor is0.029.When the temperature rises to 250℃,the weight loss rate of PI-18 nanofiber membrane is 5%.Secondly,in order to reduce the air filtration resistance of PI nanofiber membrane and reduce the load of the purification system,by changing the fiber morphology and structure,PAA and SiO₂microspheres are blended to form a PI/SiO₂nanofiber membrane with a convex structure on the fiber surface.The Stober method was improved.In the later stage,the gradient heating method was used to successfully prepare the SiO₂microspheres with directional particle size.The SiO₂microspheres were blended with PAA solution and spun.By adjusting the content of SiO₂microspheres,the PI/SiO₂nanofiber membranes with different content of SiO₂microspheres were prepared.The results showed that the introduction of SiO₂microspheres reduced the fiber diameter,the rough structure of the fiber surface increased the specific surface area of the fiber membrane,improved the probability of catching particles by the micro nano fiber membrane,and the SiO₂microspheres increased the distance between fibers,reduced the fiber stacking density,and reduced the air filtration resistance.The filtration efficiency,pressure drop,and quality factor of the PI/SiO₂nanofiber membrane were 99.669%,171.3 Pa,and 0.033 Pa-1,respectively,Co MPared with PI nanofiber membrane,the pressure drop is reduced by40Pa.Moreover,the hybrid of organic and inorganic materials further improved its thermal stability.When the temperature rose to 250℃,the quality of PI/SiO₂nanofiber membrane almost did not change,the weight loss rate was not more than1%,and the heat resistance was excellent.Finally,in order to endow PI/SiO₂nanofiber membrane with formaldehyde adsorption performance,metal organic framework material（ZIF-8）was introduced on its surface to prepare PI/SiO₂@ZIF-8 Composite nanofiber membrane.Firstly,aminated ZIF-8 nanocrystalline powder was prepared by hydrothermal synthesis,epoxy group was introduced on the surface of PI/SiO₂nanofiber membrane by UV light graft polymerization,and then ZIF-8 was assembled on the surface of PI/SiO₂nanofiber membrane by ring opening polymerization.The results showed that under the combined action of chemical adsorption and electrostatic adsorption,PI/SiO₂@ZIF-8 The filtration efficiency of the composite nanofiber membrane is as high as 99.703%,the pressure drop is maintained at 178.7 Pa,and the quality factor is0.0326.When the temperature rises to 300℃,the weight loss rate is only 4%,and the heat resistance is excellent.And within 4h,PI/SiO₂@ZIF-8 The saturated adsorption capacity of the composite nanofiber membrane for formaldehyde is 41.58mg/g,more than 12 times that of the PI/SiO₂nanofiber membrane without ZIF-8 modification,and it has excellent formaldehyde adsorption performance.