Application Of Aramid Nanofiber Coated Nonwovens For High Temperature Filtration

High temperature filter material is mainly used in the filtration of industrial high temperature gas,and thereby playing an important role in controlling industrial flue gas pollution to the environment.High-temperature filter material first requires the material to have high temperature resistance and good boiler effect.In addition,the material also has a certain chemical stability and mechanical strength.PTFE coated nonwoven needle filter material has good heat resistance,filtration and chemical stability,making it widely applied in the field of high temperature filtration.However,the mechanical strength of PTFE microporous membrane is relatively poor,which leads to a high risk of damage during operation.Therefore,finding a microporous membrane with heat resistance,filtration efficiency and chemical stability and high strength to replace the PTFE membrane to prepare a high-temperature filtration material is of practical significance.The main research topic of this thesis is to cleave the para-aramid fibers in dimethyl sulfoxide solvent by a solvent-based method to obtain nanometer-level aramid fibers,which are called as nanofluid dispersion of aramid fibers(ANF).Due to the negative charge of aramid fiber,the aramid nanofibers can be laminated with the positively charged electret nonwoven materials by layer-by-layer assembly.when the ANF continue to gather on the surface of nonwoven fabric,a thin layer of aramid nanofiber membrane was formed,resulting in a nonwoven composite covered with aramid nanofiber film.The aramid nanofiber membrane shows high strength,high wear,high temperature resistance and high filtration efficiency,which is suitable for high-precision high-temperature filtration.Through opimizing the preparation process of the aramid nanofiber dispersion and subsequent characterization of the aramid nanofiber coated nonwovens,the following conclusion has been reached:(1)When placing aramid fiber in dimethyl sulfoxide(alkaline environment),the H atoms on the molecular chain will be stripped,leading to the breakage of hydrogen bond between the molecular chains.The molecular chain fractures and the macro-scale para-aramid fibers are cleaved into aramid nanofibers of 5-10 micrometers in length and 20-30 nanometers in diameter.These nanofibers can be evenly dispersed in dimethyl sulfoxide to form a transparent,dark red nanofiber dispersion.(2)As aramid nanofibers have negative charges,they would spontaneously bonded with nonwovens after positive electret due to the attraction between positive and negative charges.The surface of the nonwoven can be readily coated with a layer of aramid nanofibers through the layered-by-layered self-assembly method.(3)Compared with the conventional PTFE coated high-temperature filter material,the aramid fiber coated material shows the advantages including high strength,high temperature resistance,small pore diameter,uniform pore size distribution and high filtration efficiency,which are desirable for high temperature filtration materials.In summary,with the in-depth study of nanofiber dispersion technology and process optimization,aramid nanofiber coated nonwoven filters are prepared,which may become a promising candidate for high temperature filtration.