关键词: 静电纺丝, 二次分形螺旋结构, 有限元分析, 电场强度

Abstract: The electrospinning technology is a method to stretch polymer fluids for fabricating nanofibers with diameters of tens to thousands of nanometers under the electrostatic field force, which is simple, widely applicable, and the most promising in the industrialization of nanofibers. At present, the preparation of large-scale electrospun nanofibers includes needle type and needleless type. Compared with the needle electrospinning technology, the needleless electrospinning technology has the advantages of zero needle clogging problem, easy cleaning and significantly higher production efficiency. However, the current needleless electrospinning technology used for the industrial preparation of nanofibers requires a high spinning voltage, which may break down the air, resulting in  great safety hazards, high energy consumption, wide diameter distribution and poor quality of the fibers. The fractal spiral has a self-similarity characteristic, which can improve the uniformity of the field strength of the spinning electrode based on the spiral curve in the fractal structure. The multi-spinning site characteristics of the fractal curve can improve the electric field strength and production efficiency of the electrode, so as to save energy and improve the fiber quality. Firstly, we start with the cylindrical spiral, and obtain the parametric equation of quadratic fractal spiral through space coordinate transformation, establishing the mathematical model of quadratic fractal spirals. Then, the mechanical model of the spinning unit of the fractal spinning needle is established by using the quadratic fractal spiral parameter equation, and multiple spinning units are combined to form an array of spinning needle. Finally, we change the following variables in turn while keeping other variables constant: primary radius, primary pitch, secondary radius, number of secondary disturbing turns and wire radius. By using finite element analysis software, the field strength of the spiral spinning needle with quadratic fractal structure is analyzed and the optimal structure is obtained. It is found that the electric field strength and CV value increase with the increase of the primary radius. The increase of the primary pitch can increase the electric field strength but decrease the CV value. The increase of the secondary radius, the number of secondary perturbations turns and the radius of the wire can lead to a decrease in the field strength value and has few effects on the CV value. Combined with the actual situation, the optimal parameters of fractal structure are determined as follows: primary radius of 80 mm, primary pitch of 60 mm, secondary radius of 10 mm, number of secondary disturbance turns of 40 and wire radius of 0.2 mm. The average electric field strength is 31.8 kV/cm and the CV value of the field strength is 7.53%. The results show that the structure of the spinning needle can effectively reduce the voltage required for spinning, and the energy consumption is low. Moreover, the uniform field intensity will make the electrospun nanofibers evenly distributed, which is of significance to be referred for the actual industrial production of nanofibers.

Key words: electrospinning, secondary spiral structure, finite element analysis, electric field strength