| Nanofibers have huge potential applications in areas as diverse as filtration,tissue engineering,protecting clothes,battery separators and strain sensors due to their many unique properties,including larger surface area,low density and high rate of adsorption.Electrospinning is the most commonly used method for scaled-up producing nanofibers due to its simplicity and efficiency.Electrospinning can be used to produce nanofibers from many different materials for various applications.However,the efficiency of traditional capillary needle electrospinning is very low.The productivity can be improved by multi-needle electrospinning,but it still suffers from a number of defects including needle blocking and washing.Besides,the multi-needle setup usually requires a large operating space,and the relative locations of needles have to be optimized to avoid the strong charge-repulsion between the adjacent solution jets.A new method named differential electrospinning can efficiently avoid these defects because the generation of multiple jets from differential electrospinning is self-organize.However,the existing differential electrospinning technologies still suffer some shortages including high voltage,uneven distribution of nanofiber diameter and low productivity.Therefore,a novel method named needle roller solution differential electrospinning was proposed.The research focus on the design of system of needle roller differential electrospinning,the experimental verification,electric filed distribution of needle 'piece and investigation of process parameter.The main contents are as follows:(1)The device of needle roller differential electrospinning was designed,and the experimental verification using PVA/H2O was conducted.The results show that the optimum spinning distance was 120mm,which can make jets fully stretched and finally solidified into nanofibers.And in order to continuously generate multi-jets from tips of needle piece,the voltage was at least 35kV.To ensure that spinning solution film can be uniformly covered on the tip of needle pieces,the optimum speed of the roller was 30r/min.(2)The tip effect of needle piece was studied by using finite element simulation ANSYS.The influence of the structure parameters of needle piece on the electric field distribution was systematically studied.The finite element simulation results show that the length of the needle piece did not affect the distribution of the voltage and the electric field.With the increase of the density of the needle piece,the uniformity of the electric field distribution at the tip of the needle piece was obviously improved.The simulation of various spinnerets with different structure shows that the electric field intensity at the tip of the needle piece was the largest and the distribution of the electric field was the most concentrated.In multi needle piece system,the uniformity of electric field distribution was improved with the increase of the needle piece spacing.(3)The influence of the needle piece spacing,the concentration of spinning solution and the voltage on the diameter distribution and productivity of nanofibers was systematically studied.The experimental results show that when the PVA concentration was 9wt.%and the spinning voltage was 40kV,with the increase in needle piece spacing,the diameter distribution of nanofibers was more uniform.When the needle piece spacing was 10mm and the spinning voltage was 40kV,with the increase in the solution concentration,although the nanofibers yield increased,the average fiber diameter also increased sharply,and the uniformity of diameter distribution was also poor.Increasing the spinning voltage in the appropriate range was a good way to reduce the fiber diameter,and it can also effectively stimulate more continuous multi-jets,which result in the increase in nanofibers yield.Setting the needle piece spacing was 10mm,the PVA concentration was 9wt%,when the voltage was 55kV,the fiber productivity can be as high as 13.5g/h. |
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