| The particulate matter(PM) pollution in air poses serious health threats to the public, fatally interferes with equipment operation. It contributes to the urgent need for high performance filters. By virtue of the integrated features of brief process, cost-effective, good filtration performance, etc., the fibrous filter gains its absolute mainstream status for airborne particle filtration. However, the conventional fibrous media(melt-blown fibers, glass fibers, and spun-bonded fibers) still suffer from many performance disadvantages due to their micro-sized fiber diameter, including relatively low filtration efficiency, high air resistance, low filtering precision and deep bed filtration manner, etc., Although several strategies consisting of recklessly increasing basis weight and the electret treatment have partly improved the filtration efficiency, the followed fatal flaws are brought to the conventional fibrous media, such as high energy and material consumption, and safety hazards from unexpected failures. As one of the most effective means of fiber refining, many electrospun filter media, such as poly(vinyl alcohol), polyacrylonitrile(PAN)/poly(acrylic acid), PAN/polyurethane(PU), polyvinyl chloride/PU, polyetherimide, polyamide-66(PA-66), and so on, have been successfully fabricated so far. However, some drawbacks still remain, such as, the high packing density, the limited refinement of diameter(100 nm~1 μm). According to the above problem, this thesis further optimizes the comprehensive performance of fibrous media by the electrospinning technology.Firstly, PAN dissolved in N, N- dimethyl formamide(DMF) is electrospun. Then by regulating spinning solution concentration, applied voltage respectively, we precisely regulate and control bead-on-string structure of PAN fiber membrane. Then we characterize the morphology structure and test the performance of nanofiber membrane. When the concentration of PAN is 6 wt%, the applied voltage is 30 kV, fibers membranes have the optimal filtration performance and the poor mechanical properties.Secondly, in order to improve the mechanical properties of the membrane, we add the multiwalled carbon nanotubes(MWCNTs) to spinning solution for the preparation of the MWCNTs nanocomposites. By regulating the concentration of MWCNTs, the MWCNTs@PAN nanocomposite morphology structure, membrane filtration performance and mechanical properties are discussed. When the concentration of MWCNTs is 0.05 wt%, the tensile strength of the nanocomposite membrane increases by 35%, and it also improves its filtration performance.Lastly, the performance of the composite membrane is further optimized with the introduction of nylon 6(PA-6). Here we report a strategy to design and create sandwich structured PA-6/MWCNTs@PAN/PA-6 composite membrane. Our approach allows the MWCNTs@PAN beadon-string fibers and two-dimensional PA-6 nanonets to assemble into the new filtration medium with tunable porous structure and mechanical properties on a large scale. By facilely combining with weight ratio of PA-6/MWCNTs@PAN, the resulting PA-6/MWCNTs@PAN/PA-6(1/8/1) composite membrane exhibits high filtration efficiency of 99.992%, and low pressure drop of 117.5 Pa for filtrating ultrafine airborne particles and robust mechanical properties(tensile strength of 7.3 MPa, toughness of 1.77 MJ/m3, and Young’s modulus of 130.4 MPa). The successful synthesis of PA-6/MWCNTs@PAN/PA-6 medium would not only make it a promising candidate for air filtration, but also provide new insights into the design and development of composite membranes for various applications. |
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