| In recent years,electrospinning technology,as an effective method for preparing micro-nano fibers,has many advantages,such as wide range of spinnable raw materials,strong fiber structure adjustability,strong combination of multiple technologies,and expandable preparation process.A large number of researchers are using this technology to prepare micro-nano fibers with multi-level structure in order to obtain special and novel functions.Therefore,in-depth discussion on the influence of electrospinning process parameters on the preparation of multi-stage micro-nano fibers and its forming mechanism will help to endow micro-nano fibers with different structures more efficiently and broaden their applications.Based on the research status of electrospinning micro-nano multi-stage structure,this paper uses high voltage electrospinning equipment to prepare micro-nano fibers with polystyrene(PS)and polyvinylpyrrolidone(PVP)as raw materials under the conditions of spinning voltage of 20 kv,spinning distance of 20 cm,temperature and humidity of 25±0.2℃ and 60 ±0.2% respectively.The viscosity and conductivity of the solution were characterized by NDJ-79 viscometer and EXTRE handheld conductivity tester.The Taylor cone shape and jet trajectory in the spinning process were captured by high-speed photography technology.The coaxial nozzle was simulated by ANSYS software.The apparent morphology,internal structure and chemical structure of the fiber material were characterized and analyzed by scanning electron microscope,transmission electron microscope and infrared spectrometer.The effects of polymer solution concentration,coaxial needle configuration,core/shell solution ratio and other parameters on the preparation of micro-nano fibers were studied,and the relationships between solution concentration,electric field distribution,core/shell solution ratio and Taylor cone,jet morphology and fiber structure were established.The main research results are as follows:(1)Single-nozzle electrospinning technology is adopted,and 10 wt%,20 wt%,30wt% PS and 5 wt%,25 wt%,45 wt% PVP spinning solution are respectively selected to prepare single-component micro-nano fibers.By analyzing the main processes of stretching,whipping,curing and the like in the electrospinning process,it is found that lower polymer concentration can reduce the viscosity of the solution,increase the conductivity,and obtain spherical Taylor cones and higher whipping frequency,thus obtaining fibers with bead structures with finer diameters.(2)PS/PVP core-shell fibers were prepared by coaxial electrospinning technology,using concave,planar and convex twin nozzles.By studying the relationship between electric field intensity distribution and Taylor cone shape,jet trajectory,fiber surface shape and internal structure,it is found that the core-shell fiber prepared by concave nozzle is the thinnest and has groove shape on the surface due to smaller straight jet length,larger envelope angle and higher whipping frequency.On the contrary,convex nozzle can form core-shell fiber with the thickest diameter and porous surface.(3)Grooved fibers were prepared by concave double-nozzle electrospinning with 5wt%,20 wt%,35 wt% PVP and 20 wt% PS,respectively,and the spinning solution was core-shell solution.The results show that the thickness of PS/PVP core-shell fibers increases with the increase of concentration of PVP core solution,and the fiber surface changes from a slender hole structure to a groove structure and the number of grooves increases.With the increase of concentration of PVP shell solution,the thickness of the outer layer of PVP/PS core-shell fiber is basically the same as that of the outer layer,which is a thin layer,while the inner fiber presents a multi-channel structure with different light and shade,while the fiber surface changes from a folded structure to a groove structure,and the number of grooves increases. |
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