Preparation And Characterization Of PTFE Micro-nano Fiber Aerogel

In the modern industrial production process,the field involving filtration and purification of dust-containing gas is very wide,especially the high-temperature gas purification and dust removal technology,which is an indispensable part of environmental protection.Among the numerous high-temperature gas purification and dust removal technologies,the bag-type dust removal technology is most widely used for its advantages of economy and high efficiency.In recent years,with the gradual tightening of national dust removal standards,the requirements for the filtration accuracy of the filter media have become stricter.However,at present,most of the filter materials used in China are micron-level fibers.There are certain bottlenecks of those filter materials while achieving the goal of high efficiency and low resistance,and its performance structure needs to be further improved.In this time,the innovative design of the structure of the filter material will be an effective way to develop a new type of high-efficiency and low-resistance filter material.Nanofiber aerogel is a kind of 3D high bulky fibrous aggregates with low density,high porosity and high specific surface area.The zigzag opening channels of nanofiber aerogel make it possiable to capture particles on a long transmission path,so it has the potential in the design of filter material with high filtration efficiency and low pressure drop.At present,there is relatively little research on the use of nanofiber aerogels for high-temperature flue gas filtration,and new nanofiber aerogel materials in this field have yet to be developed.Polytetrafluoroethylene?PTFE?is a common material in the field of high temperature dust removal,which has outstanding temperature resistance,solvent resistance,waterproof and oil repellent advantages.In this study,we attempted to prepare PTFE-based micro-nanofiber aerogels through electrospinning,vacuum freeze-drying,and heat consolidation technology.The electrospun polyamic acid?PAAs?nanofibers which could be derived into polyimide?PI?were introduced into the PTFE nanofiber aerogel as the reinforcement phase to ensure the stability of three-dimensional structure of the composite nanofiber aerogel.In order to further improve the porosity,shrinkage and filtration performance of the composite nanofiber aerogel,PTFE-polyamideimide?PAI?nanofibers were used to composited with PAAs fibers by replacing PTFE nanofibers,then PTFE-PAI/PI nanofiber aerogel was preparated.The main research contents and conclusions of this thesis were as follows:?1?Preparation and collection of nanofiber membranesPTFE-Polyethylene oxide?PEO?nanofibers,polyamic acid?PAAs?nanofibers,and PTFE-polyamideimide?PAI?-PEO nanofibers with good appearance were prepared through the adjustment of spinning solution ratio and electrospinning parameters,which were raw material of subsequent aerogel preparation.The results show that the ratio of different components in the spinning solution and the electrospinning process parameters such as spinning flow rate all played significant roles in the nanofiber morphology and diameter.When the mass ratio of PEO:PTFE:H₂O=1:10:4,the spinning flow rate was 0.8 mL/h,the spinning voltage was 20 kV,and the receiving distance was 18 cm,a uniform thickness PTFE-PEO nanofibers with the diameter of 442±43 nm was achieved;While the spinning flow rate was 0.5 mL/h,spinning voltage was 15 kV,the receiving distance was 18 cm,the PAAs nanofibers with a diameter of 341±54 nm could be obtained;Whlie PEO:PTFE:H₂O=1:10:19,PAI:PTFE=3:7,the spinning flow rate was 0.8 m L/h,the spinning voltage was 18 kV and the receiving distance was 18 cm,then PTFE-PAI-PEO nanofibers with a diameter of 402±53 nm was collected.?2?Preparation of PTFE/PI nanofiber aerogelIn view of the problems of structural collapse and severe volume shrinkage during the preparation of PTFE nanofibers aerogel,in this section,PAAs nanofibers were mixed with PTFE nanofibers through the homogenization process as the support reinforcement materials.After freeze-drying and sintering process,PTFE/PI nanofiber aerogel was achieved.The effect of the ratio of PAAs nanofiber,the fiber content in suspension and the sintering temperature on nanofiber aerogel structure,thermodynamics,filtration were studied.The results show that addition of PAAs nanofibers could effectively reduce the collapse shrinkage behavior during the preparation of nanofiber aerogels,and the excellent thermal properties of PI could also increase the decomposition temperature of nanofiber aerogels.When the mass ratio of PAAs:PTFE was 4:6,the fiber content in the suspension was 1%,and the sintering temperature was 300 ^oC,the obtained PTFE/PI composite nanofiber aerogel presented good morphology,the porosity was above 98%,the thermal decomposition temperature was higher than 556 ^oC and the filtration efficiency of PM2.0 was exceeded 98.52%.?3?Preparation of PTFE-PAI/PI nanofiber aerogelThe addition of PI nanofibers could effectively improve the formation of nanofiber aerogel.However,the filtration performance of aerogel still needed to be improved.In this section,in order to further optimize the pore structure and filtration performance of PTFE-based nanofiber aerogel,the blended PTFE-PAI-PEO nanofiber was used to mixed with the PAAs nanofiber by replacing PTFE nanofiber.Then PTFE-PAI/PI nanofiber aerogel was prepared after the aforementioned process.Similarly,the mixing ratio of the two fibers,the fiber content and sintering temperature were explored.The results show that:the ratio of PAAs nanofibers,the fiber content in the suspension,and the sintering temperature were still significant factors that affected the quality of nanofiber aerogel.The change of the parameter directly affected the fiber morphology and performance.Compared with PTFE/PI nanofiber aerogel,the volume shrinkage,porosity and filtration performance of PTFE-PAI/PI nanofiber aerogel obtained with the addition of PAI had been greatly improved.When the mass ratio of PAAs and PTFE-PAI nanofiber was 5:5,the fiber solid content was 1%and sintering temperature at 400 ^oC,the as-prepared PTFE-PAI/PI composite nanofiber aerogel would possess good morphology,high porosity?above 98.7%?,high thermal stability?the decomposition temperature was above 505°C?and good filtration efficiency?the filtration efficiency to PM2.0 was over 99.92%?.