Preparation And Properties Study Of Electrospun Porous Nanofibers

Because of ultra high specific surface and excellent properties, porous materials,which are potentially of great technological interest for the development of biology,medicine, energy, environment, advanced manufacturing technology, have attracted muchattention as the most promising material. Porous materials can be prepared byhydrothermal synthesis method, sol-gel method, electrospinning and other methods.Electrospinning has been recognized as a simple and efficient technique for the fabricationof polymer nanofibers. Recently, research shows electrospun porous materials can beobtained simply by adjusting electrospinning parameters or postprocessing nanofibers. Theporous structure further enlarges the specific surface area and enhances the hydrophobicproperty of the electrospun nanofibers, which alters the performance of the electrospunnanofibers greatly.In this paper, electrospun porous nanofibers were prepared by controlling solventsystem, electrospinning parameters and weight ratio in polymer blend. And the propertiesof obtained nanofiber mats were investigated. Theoretical analysis and experiment researchwere carried out to research mechanical mechanism of electrospun porous nanofibers, andcould be used to optimize and control the porous structure.The effect of solvent evaporability on morphology and properties of electrospunnanofiber was studied firstly. With the increase of high volatility solvent chloroform inmixed solvent system, the beads gradually reduced and the surface of the nanofiberchanged from roughness to formation of the pores. The pore structure further enlarges theporosity and enhances the hydrophobic property of the electrospun nanofiber.To research the effect of electrospinning parameters on porous nanofiber, asimplifying gas-liquid two-phase flow model was established. Based on the model, theeffects of various spinning parameters on quality of product, such as the number ofnanopores and diameter, will be systematically carried out. With the increase of the volumeflow rate or the decrease of the applied voltage and the collect distance, the diameter of porous nanofibers decreased. The theoretical analysis results were further verifiedaccording to the experimental data. In addition, Bernoulli equation was used to study theelectrospinning “splaying” process. We found the ratio of pore width to pore length isvaried along with the variation of the internal pressure of the jet, and the internal pressureof the jet increases with the velocity of the charged jet decreases. When the primary jetsplitting into two filaments, the ratio of pore width to pore length decreases, the pores ofthe fiber will collapse.Then, in order to study the effect of humidity and nonsolvent on electrospun porousnanofibers, the porous polyacrylonitrile nanofibers were prepared by regulating thespinning humidity or introducing nonsolvent in the solvent system. The diameter of thepolyacrylonitrile nanofiber increased with the increase of PAN and humidity. And with theincrease of humidity, surface features, or pores, of the nanofibers became evident, theporosity of the porous nanofiber membrane increased, and the tensile strength andelongation of the membrane decreased. Moreover, the introduction of nonsolvent in thesolvent system also made the surface of the nanofiber formed porous structure, and theporosity of electrospun nanofiber membrane increased.Finally, the electrospun bicomponent nanofibers were obtained, and the two polymerswere phase separated in the nanofibers. Then the domains of the dispersed phase wereselectively removed, internal pores could be generated, and porous nanofibers wereproduced. Results show that with the increase of PLA in the mixture, the breaking strengthof the nanofibers decreased and the porosity of the nanofiber membrane increased. Afterthe chloroform treatment, the porosity of the porous nanofibers membrane increasedsignificantly, and the breaking strength of the porous nanofiber membrane decreasedobviously.