Study On The Forming Mechanism Of Electrostatic Spinning Nanometer Fiber And The Double - Scale Nano - Fiber Composite Filtration Material

Nanofibers are widely used in the fields of environmental protection, tissue engineering, health protection, catalysis and sensors because of their small diameter, high specific surface area, and good adsorption performance etc. Electrospinning technique, which utilizes the high voltage electric field force, is an usual way for the efficient nanofiber preparation. New electrospinning devices and technique have introduced huge concern regarding the bulk production limitations of traditional capillary needle electrospinning technology due to its drawbacks such as low yield, blocking and cleaning difficulties.In this dissertation, a new solid-pin electrospinning technology was proposed. The operation principle can be expressed as that the spinning solution covered the solid-pin top surface formed Taylor cone and further generated jets under the electric field force which was formed between the solid pin electrode and the grounded receptor with the help of the high voltage electrostatic generator. The experimental verification was conducted based on the electric field strength simulation and the solid pin structure optimization as well as the force analysis of the liquid drop on the top of solid pin and the theoretical derivation of critical voltage. In addition, the preparation and performances of the double-scale nanofiber composite filter material via solid-pin electrospinning were studied. The research would provide theoretical and experimental basis for the development of nanofibers through new electrospinning technology.Firstly, the solid-pin electrospinning device, which is consisted to be the solid pin electrode, high voltage electrostatic generator, flat-type receptor and circulating fluid supply system was designed, The experimental verification systems included the inorganic sol-gel solutions and the organic systems such as the poly(vinyl alcohol) (PVA)H2O, polyamide (PA6)/formicacid, polyacrylonitrile (PAN)/N,N-dimethylformamide (DMF), and polyvinyl fluoride (PVDF)/N/,N-dimethylacetamide (DMAc)/acetone. The results showed that the PVA, PA6, PAN and PVDF nanofibers possessed good morphologies. The soli-pin electrospinning technology displayed good universality for organic polymer solutions. Evenmore, it showed the higher efficiency than traditional capillary needle electrospinning technology, and eliminated blocking and cleaning. This paper also verified the feasibility of the preparation of inorganic ultrafine fiber with high viscosity silicon aluminum sol or CuC12/Ce(NO3)/aluminum sol mixture aqueous solution. The results indicated that solid pin electrospinning showed poor suitable for high viscosity inorganic gel system. Electro-blown spinning technique could successfully fabricate porous inorganic composite fiber, however, the low production efficiency limited its popularization in the field of large-scale production.Secondly, the model of solid-pin electrospinning process was constructed based on Maxwell electromagnetic equations and finite element analysis (FEM) simulation. The effects of the solid pin electrode form, receptor type and the process parameters on the intensity and distribution of electric field were studied. The results indicated that the electrode form affected the intensity and distribution of electric field significantly. The maximum electric field strength existed where the shape change curvature was bigger and increased with the sharp degree. The electric field intensity vector implied that the electric field vector end at the bottom of narrow arc area of the drum-type receptor and the flat-type receptor favored the nanofibers diffusion deposition. The simulation results of the process parameters demonstrated that the applied voltage had a linear positive correlation with the electric field strength, and the two power of the work distance was negatively correlated with the strength of the electric field.Thirdly, two feeding models with different solid pin electrode forms, arc and tip, were designed. The force analysis of the charged liquid droplet on the top of solid pin was compared. The correction factor, k, associated with work distance during solid-pin electrospinning was obtained from the simulation results of multi-solid-pin and flat-type receptor. Additionally, based on the calculation formula of the charged Rayleigh liquid droplet, it was theoretically derived that the critical voltage to generate jet from liquid dropleton the top of the solid pin electrode was a function of the work distance, the size of the solid pin electrode and the surface tension of the solution.Next, the relationship between the morphology and yield of the obtained nanofibers and the size of the solid pin electrode and the electrospinning process parameters (spinning solution concentration, applied voltage and work distance) was evaluated. The results indicated that smaller solid pin electrode and lower concentration spinning solution were beneficial to obtain nanofibers with thinner diameter, but delimental to the yeild. The elevation of applied voltage favored the diameter decrease and the jets generation, thus the increase of nanofibers yield. The higher electric field strength on the top of the solid pin under small work distance led to high electrospinning efficiency. Nevertheless, too small work distance may cause nanofibers bonding and ribbon nanofibers.Finally, double-scale PA6 nano-/micro-fiber filter material deposited on spunbond nonwoven with good mechanical performance was prepared via multi-solid-pin electrospinning to overcome the poor mechanical property and high filtration resistance. The effect of the combination of nanofibers with different diameters on the filtration property was assessed. The results showed that double-scale nanofibersfilter material combined with thick nanofibers (300-500 nm) and thin nanofibers (60-100 nm) was obtained using spinning solutions with two different concentrations. The combination of the good adsorption property of small scale nanofibers and the skeleton support of lager scale nanofibers made the composition nanofiber filter material showed high filtration efficiency and low filtration resistance. The filtration resistance of the double-scale nanofiber filter material decreased up to 20% compared to that of the single-scale nanofiber filter material with the same filtration efficiency.