Preparation And Performance Study Of High Temperature Resistant Polyimide Nanofiber Filtration Material

With the rapid development of industrial technology,air pollution has seriously threatened the living environment and health of human beings.Particularly,fine particles with diameters ranging from 0.1 to 2.5?m,also known as PM_2.5,have been classified as a first-level carcinogen by the World Health Organization(WHO),since they can carry numerous toxic compounds and penetrate deep into the lungs.In order to solve air pollution,aramid fiber,glass fiber and polytetrafluoroethylene(PTFE)filter materials have been widely used in the field of high temperature air filtration.However,the filtration efficiency is difficult to reach the standard of industrial waste gas purification.It is of great significance to achieve high-efficiency filtration performance and long-term use for the high-temperature resistant filter material.In order to realize the development of high temperature resistant filter materials,we use electrospinning equipment to prepare PI nanofiber membranes.In addition,we prepared the PI nanofiber membrane composite filter material through the ultrasonic composite device.The resulted composite filtration material shows high mechanical properties.Firstly,we explored the influence of polymer concentration and lithium chloride(LiCl)concentration on the morphology and performance of PI nanofiber membranes.It is determined that when the polymer concentration is 18 wt%and the LiCl concentration is 0.006 wt%,the PI nanofiber membrane has the best filtration performance.Under this concentration condition,the filtration efficiency of PI nanofiber membrane is 99.3%,and the pressure drop resistance is only131 Pa,showing high-efficiency removal performance for PM_0.3filtration.Secondly,we studied the imidization process of PI nanofiber membrane.The results show that the optimal heat treatment temperature and time are 300?and 40 min,respectively.After the imidization treatment,the average fiber diameter decreased,and the fibers contracted and bent.Its filtration efficiency has reached more than 99%,the pressure drop resistance is only 116 Pa,the breaking strength is 3.9 MPa,and it has only 1%weight loss rate in a high temperature environment of 250?.Finally,in order to enhance the performance of PI nanofibers,we use ultrasonic composite device to prepare aramid fiber needle-punched felt and PI nanofiber membrane into composite filter materials.The porous films bond the aramid fiber needle-punched felt and PI nanofiber membrane.The breaking strength of PI nanofiber membrane composite filter material can reach24.6 MPa at room temperature.After storing the PI nanofiber membrane composite filter material at a high temperature of 250°C for 12 hours,its breaking strength can still reach 22.4 MPa.It proves that PI nanofiber membrane composite filter material has high temperature resistance.PI nanofiber membrane composite filter material has excellent filtration performance.Its filtration efficiency is 99.96%,pressure drop resistance is 138 Pa,and quality factor is 0.0567 Pa^-1under the wind speed of 32 L/min.When the wind speed is 52 L/min,the filtration efficiency of the composite filter material is 99.92%,the pressure drop resistance is 256 Pa,and the quality factor remains above 0.02 Pa^-1.After ten times dust cycle filtration,the filtration efficiency of PM_2.5particles can still be maintained at 50?g/(m³·min).It proves that PI nanofiber membrane has long-term and high-efficiency PM_2.5particle filtering ability.