Design And Performance Characterization Of PAN Pre-oxidized Fiber Filter

In the process of entanglement,fibers with barbed needles transferred from the horizontal to the vertical plane,meanwhile,the fibers bend,curl and one part of them remains in the thickness direction.These would result in a reduction of the straight segment fiber length within the horizontal plane.The shorter the straight segment fiber length,the higher degree of fiber entanglement.Based on the this,it is suggested that the straight segment fiber length can give an indication of the fiber entanglement.Image analysis method based on Hough transform could effectively and directly detect the fiber straightt segment.Therefore,this method was applied for obtaining fiber straight segment orientation and length index.In this paper,the straight segment fiber length index and orientation,take the development of pre-oxidized(OPAN)fiber filters as the example,were used to guide the design of non woven fiber filters.Firstly,acoording to the variation of straight segment fiber length,the straight segment fiber length can give an indication of the fiber entanglement.The fiber straight segments were detected to obtain the information of straight segment fiber orientation and length index with image analysis based on Hough transform.Combining the entanglement coefficient method and the analysis results of needling parameters influencing on fiber entanglement,the availability of fiber entanglement indicated by straight segment fiber length index.The optimum parameters of OPAN fiber needle punched nonwoven were obtained:punch frequency of 240 strokes/min,needle penetration depth of 6 mm and punch times of 2,which were verified through orthogonal experiment mehod.Secondly,the composite filters were prepared with different fiber entanglement though the method of adding PPS fiber or Nomex fiber into OPAN fiber.Taking the straight segment fiber length index into consideration,it was investigated that the influence of fiber entanglement on the mechanical properties and filtration performances of composite filters.With the increase of weight percentage of PPS fiber or nomex fiber,the fiber entanglement was increased and the mechanical properties and filtration efficiency of filters were improved.In oreder to improve the filtration efficiency of composite filters influenced by low fiaber entanglement,foam coating finish was used for the filters.After foam coating,the surface of composite filters appeared membrane attachment,becoming tighter and smoother,which increased the filtration efficiency for fine particles,and improved the dust-cleaning performances.Under the temperature of 200 ?,the filtration efficiency was as high as above 99.9%.Lastly,the influence of fiber orientation on the properties of fiber filters was investigated based on image analysis and electrospinning.It was found that the values of fiber orientation orthotropic ratios-theoretical in the range of values of fiber orientation orthotropic ratios-experimental,indicating that fiber orientation was the main effects on mechanical orthotropic of nanofiber membrane.The pores of random fiber membrane were made by interconnect fibers,and the pore size was small and forming circuitous structure,which would capture suspended particles.However,the pores of aligned fiber membrane were formed with the gaps between adjacent aligned fibers,and the pore sizes were greater and provided many channels through which particles can escape.As a result,the filtration efficiency and pressure drop of aligned fiber membrane were lower than that of random fiber membrane,which was in agree with the results of numerical simulation reported in previous literatures.The composite nanfiber membrane designed in the liture had excellent mechanical and filtration properties.Then,the composite membrane was carried out with the process of preoxidization to prepar OPAN nanofiber filter.