| In recent years,sub-micro fibers with advanced functions have set off a research boom in the fields of filtration,bioengineering and textiles industry.On account of simple principle and wide selection of materials,electrospinning technology has opened a world of opportunities for sub-micro fibers with progressive functions.It has expanded from the initial single-needle device to the needleless electrospinning technology,which solves the problem of needle blockage and low yield of sub-micro fibers.However,in the exploration of needleless electrospinning,the research on multi-jet formation control and fiber film-forming characteristics is not perfect,resulting in the shortcomings of simple structure and low added value of sub-micro fibrous membranes,which limit its applications in advanced functional fields.Based on the existing problems,this study proposed a novel electrospinning spinneret,which controls the electric field distribution by designing evenly arranged holes on surface.On the basis of steadily increasing the fiber yield,the controllable preparation of sub-micro fibers with bimodal distribution was realized.Firstly,through ANSYS Maxwell software,the optimal geometric parameters of the spinneret were determined as follows:the rotating spinneret was a multi-hole ball with 7 cm diameter,in which,there were three rings of small holes（18 holes in total）.The upper diameter of the hole was 8 mm,the base diameter was 6 mm,the depth was 3 mm and the incline angle was 30°.Simulation results showed that the thin liquid surface formed at small hole would accumulate more charge density and generate stronger electric field intensity at a constant applied potential.Electrospinning experiments showed that the multi-hole curved surface rotary spinneret has a great potential advantage in improving productivity of sub-micro fibers.Secondly,based on the theory of electrohydrodynamics,the relationship between the charged liquid film and the electric field distribution,as well as the relationship between the spinning jet and the electric field force were investigated.Then analyzed the control effect of applied voltage and polyacrylonitrile（PAN）solution concentration on fiber diameter distribution.The outcomes showed that when the solution concentration was 14-16 wt%,bimodal distribution sub-micro fibrous membranes were successfully fabricated.And increasing the applied voltage,the bimodal position of fiber diameter shifted to the left;increasing the solution concentration,the bimodal position of fiber diameter shifted to the right.Finally,the effects of different spinning process parameters have been investigated by adopting quadratic general rotary unitized design（QGRUD）to optimize the bimodal distribution sub-micro fiber yield.The outcomes showed that the optimum solution concentration,applied voltage and spinneret rotation speed on the tensile strength of sub-micro fibrous membranes were confirmed to be 14.71 wt%,48.65 k V and 1.00 r/min.The optimum parameters on the sub-micro fiber yield were confirmed to be 15.48 wt%,51.98 k V and 0.99r/min,respectively.Afterwards,spinning experiments were carried out using the multi-hole curved surface rotary spinneret and spherical spinneret to explore the influence of two fiber membrane structures on pore size distribution,filtration and air permeability.The results showed that,compared with the narrow diameter distribution sub-micro fibrous membranes,the bimodal distribution sub-micro fibrous membranes had smaller average pore size and wider pore size distribution;When the solution concentration was 16 wt%,the filtration efficiency of bimodal and narrow sub-micro fibrous membranes were lost to 97.14%and 96.07%,respectively,but the filtration resistance of the former was significantly reduced to 57.86 Pa,the quality factor reached 0.0614 Pa-1,and the filtration performance was better;Moreover,the bimodal distribution structure increased the movement path of the gas,giving the sub-micro fibrous membrane an optimal air permeability of 473.81 mm/s. |
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