Preparation And Air Filtration Properties Of Electrospun Polyimide-Based Nanofiber Membrane

In recent years,there has been increasing concern about the harmful effects of fine particles matters（PM）because PM can be absorbed by the body and deposited in the body eventually.For example,PM_2.5 can cause lung diseases through human tissues;PM_0.3 can easily enter the lungs through the respiratory tract due to its small size,and PM_0.3 can carry a large amount of toxic substances into the bronchi and deposit in the alveoli,becoming a serious threat to human health.Because the respirable PM mainly come from the combustion process,filtering PM from high temperature polluted gases is an effective way to improve air quality and maintain human health.Electrospun nanofiber membranes with a three-dimensional mesh structure have a large number of intercommunicating pores between the nanofibers.So that it can effectively filter PM and its high porosity can ensure a low air resistance.Polyimide（PI）is an ideal material for high-temperature air filtration,however,the removal effect of traditional PI filter materials for PM_2.5 is not enough ideal to achieve the requirement of high efficiency and low resistance.In this thesis,we use electrospinning technology and select high-temperature resistant material PI is selected as the object to prepare high-efficiency and low-resistance electrospun PI-based nanofiber air filter membrane,and study its application in the field of air filtration.The main research content of this thesis is divided into the following three parts:（1）Self-supporting PI nanofiber filter membranes and high-permeability PI nanofiber membranes with diameters of about 300 nm were prepared by a two-step process by electrospinning technology.By adjusting the electrospinning parameters,exploring the conditions of thermal imidization,PI filter membrane with excellent filtration performance are obtained.Firstly,the PI nanofiber membrane with self-supporting characteristics has good thermal stability（350°C）and high PM removal efficiency,and the filtration efficiency of PI nanofiber membrane with a basis weight of14.7 g/m² can reach 99.9821%for PM_0.5 and up to 100%for PM_1.0 at an airflow rate of 4L/min.optical transparency,high filtration efficiency and low pressure drop.At an airflow rate of 16 L/min and a light transmission rate of 73.8%,the filtration efficiency of high permeability PI nanofiber membrane for PM_1.0 can reach 93.241%,the pressure drop is lower than 50 Pa,and the quality factor is 0.1632.Finally,the filtration mechanism of PI nanofibers membrane is analyzed.（2）In order to further improve the filtration efficiency and reduce the air resistance of PI nanofiber membranes,Zeolitic Imidazolate Frameworks-8（ZIF-8）nanoparticles were selected to modify PI nanofibers in this thesis,and PI/ZIF-8 nanofiber filter membranes with ultra-high filtration efficiency and high temperature resistance were prepared.The smooth PI fiber surface was transformed into a rough surface structure to increase the porosity and specific surface area of the filter membrane,thus improving the overall filtration performance.In this thesis,ZIF-8 was introduced into polyimide acid（PAA）precursor solution,and PAA/ZIF-8 nanofiber membrane was prepared by doped co-electrospinning method and obtained PI/ZIF-8 nanofiber membrane by thermal imidization.ZIF-8/PI multifunctional nanofiber membrane possess 100%filtration efficiency PM_0.3,a low pressure drop of only 63 Pa,Quality Factor of 0.2888,tensile strength of 3.34 MPa,and could stably used at 350°C.Obviously,the introduction of ZIF-8 nanoparticles improve the comprehensive filtration performance of PI and maintaining its excellent high temperature resistance and mechanical properties,can be used in the field of ultra-high efficiency high temperature air filtration.（3）In order to further expand the application scenarios of PI-based nanofiber filter meterials,we prepared PI/chitosan（CTS）multilayer composite nanofiber membrane window screen air filter with high optical transmittance and antibacterial property.PAA nanofiber membrane was prepared on metal window screen by electrospinning method,and PAA nanofiber membrane was transformed into PI nanofiber membrane by thermal imidation method.Then PI membrane was installed on the receiver of electrospinning machine,and CTS nanofiber membrane was electrospun on the PI nanofiber membrane.Then,the composite electrospun PI/CTS antibacterial window screen air filter material is prepared.When the airflow velocity is 14 L/min,the filtration efficiency of PM_1.0 is95.6%,the pressure drop is 28.8 Pa,the antibacterial rates of E.coli and S.aureus is 98.36%and 96.12%,respectively.Experimental result demonstrates that PI/CTS composite nanofiber membrane not only possesses high air filtration efficiency,but also has excellent antibacterial activity against E-coli and Staphylococcus aureus,having great application potential in the field of high-efficiency filtration antibacterial window screen.