Preparation And Properties Of High Temperature Resistant PI Nanofiber Composite Filter Material

The rapid development of industry has brought people not only the improvement of life quality,but also the aggravation of environmental pollution.These pollution phenomena can be seen everywhere,such as the emission of high-temperature exhaust gas from industry and the combustion of wastes,not only are these gases extremely toxic at high temperatures,they are also associated with the release of large amounts of particulate matter（PM）,which can be very serious if inhaled.Getting rid of pollutants at source is one of the most effective solutions.However,the existing heat-resistant air filtration materials for PM0.3 and other small particle filtration efficiency is insufficient.Continuous nanofibers can be prepared by electrospinning in large quantities,and it is expected to be a high-temperature resistant filter material with high efficiency and low resistance by combining it with traditional high-temperature resistant materials.In this study,the high-temperature resistant material polyimide（PI）was used as the raw material,and the electrospun nanofibers were used as the high-efficiency filter materials,furthermore,the structure of PI nanofiber membrane was optimized and the filtration performance was improved by using PMIA superfine nanofiber,finally,the composite filter material with“Gradient”structure was prepared with P84 needled felt,and its practical application in high temperature filtration field was explored.First,the optimal formulation of polyimide nanofibers was determined,and three kinds of polyimide nanofiber membranes were prepared by a two-step process.After adjusting the concentration of PAA solution and TBAC solution,the optimal spinning solution concentration and salt concentration were obtained,and then the PI nanofiber membrane was prepared by thermal imidization.The results of SEM showed that the physical cross-linking between PI_ODA-BPDA and PI_ODA-ODPA nanofibers occurred in different degrees,which was directly reflected in the mechanical properties.The mechanical properties of PI_ODA-BPDAnanofiber membranes were similar to that of PI_ODA-ODPA,about 12 MPa,and higher than that of PI_ODA-PMDA.The results of filtration test show that PI_ODA-BPDA has the largest quality factor and the best filtration performance.The PI_ODA-BPDA was selected as the main object of the next research based on the performance characterization results of the three kinds of PI.Subsequently,PMIA ultrafine nanofibers（30-60nm in diameter）were prepared by dilute solution,high conductivity method and electrospinning on PI_ODA-BPDA substrate.First,the effect of Li Cl concentration in solution on the formation of ultrafine fibers was investigated.When the concentration of Li Cl in solution was 2 wt%,only a small amount of PMIA ultrafine fibers were observed.Therefore,TBAC was introduced to regulate the liquid surface tension at the tip of Taylor Cone.Based on this,we prepared PI/PMIA nanofiber membranes with different thickness ratios and tested their SEM,mechanical,pore size,thermal and filtration properties,the porosity was 91.87%,the filtration efficiency was 98.5%,the filtration resistance was only 124 Pa,the removal efficiency of PM0.3,PM2.5 and PM10 was98.47%,99.36%and 100%respectively at 300°C.Finally,the high temperature resistant PI/PMIA/P84 composite filtration material was prepared by using 1:1 PI/PMIA bilayer nanofiber membrane as the core filtration material.The results show that the double-layer PI/PMIA/P84 composite filtration material has stable high temperature resistance,the filtration efficiency of PM0.3 is up to 99.96%,and the filtration resistance is 293 Pa,the strength of PI/PMIA double-layer nanofiber membrane and P84 substrate is 974.28 Pa.The results of high temperature filtration test showed that the removal efficiencies of PM0.3,PM2.5 and PM10 were 98.87%,99.48%and 100%at 300°C.After heating for 48 hours at 300°C,the removal efficiency of PM0.3 could still reach 98.5%.The results of automobile exhaust filtration test showed that the removal efficiencies of PM0.3,PM2.5 and PM10 were 99.32%,99.99%and 100%,respectively,the removal efficiency of PM0.3 is 2.78 times higher than that of P84 needled felt.It can be seen that the PI/PMIA/P84 composite filtration material prepared in this paper can improve the problems of low filtration efficiency and single filtration structure of traditional filtration materials,and provide a new solution to the problem of high temperature waste gas filtration,it has a broad application prospect in the field of high temperature resistant filtration.