| Nano materials and porous materials have the characteristics of high specific surface area, high porosity, high surface activity, strong adsorption and so on, and have shown a great application prospect in environmental science, biological medicine, energy, chemical engineering and national defense, etc. Electrospinning is a convenient, direct and economical method for producing nano fiber materials, the porous structure of fiber materials can be simply obtained by post processing or adjusting the electrospinning parameters. Electrospraying is a new method for the preparation of porous polymer microspheres in recent years. The porous structure increases the specific surface area of the materials, and gives them new excellent properties, makes them have great potential applications in a wider field.In this paper, PVDF fibers and PVDF porous fibers were prepared via electrospinning technology, while PVDF porous microspheres were prepared via electrospraying technology. Properties of the solution and the prepared samples were characterized by using a combination of rotary viscometer, scanning electron microscopy and specific surface area and pore size analyzer. The diameters of fibers and microspheres were statistically determined by using the image analysis software ImageJ The effects of solution properties and processing parameters on the preparation of samples were studied, which provide theoretical and experimental basis for the preparation of PVDF fibers and PVDF porous fibers as well as PVDF porous microspheres. The main conclusions of this paper are as follows:1、Preparation of PVDF fibers via electrospinning:As the solution concentration increases, the rotational viscosity of the solution and the diameter of the fibers increase exponentially, there are polymer beads when the solution concentration is low, and beads decrease and finally disappear along with the increase of solution concentration; With the increase of the proportion of acetone in the mixed solvent of DMF/acetone, the rotational viscosity of the solution decreases, the diameter of the fibers becomes larger, and the surface of the fibers change from smooth to rough; With the increase of electrospinning voltage, the average diameter of the PVDF fibers decreases after increase; With the increase of electro spinning speed, the average diameter of PVDF fibers increases linearly; With the increase of the collecting distance, the average diameter of PVDF fibers increases after decrease, and the fibers are bonded when the collecting distance is too close, while the polymer beads appear and gradually increase when the collecting distance is too far; PVDF fibers with smooth surface, uniform diameter distribution and no beads as well as bonding defects with an average diameter of 0.39μm can be obtained via electrospinning when the mass percentage concentration of PVDF solution is 20wt%, DMF/acetone volume ratio is 8:2, electrospinning voltage is 15kV, the electrospinning speed is 2.0ml/h and the collecting distance is 15cm.2、Preparation of PVDF porous fibers via electrospinning of blend polymers:Phase separation occurr in two groups of fibers after electrospinning of PVDF/PEG or PVDF/PVP blend polymers solution, and the porous structure of PVDF fibers can be obtained by using the ethanol/water mixed solvent to selectively dissolve the PEG or PVP; Using PEG as a pore forming agent, with the increase of PEG molecular weight, the average diameter of PVDF porous fibers gradually increases, the porous structure first increases and then decreases, and the effect is best when the PEG molecular weight is 6,000; When the molecular weight of PEG is 6,000, the specific surface area, total pore volume and average pore diameter of PVDF porous fibers increase gradually with the increase of PEG dosage; Using PVP as a pore forming agent, the specific surface area, total pore volume and average pore diameter of PVDF porous fibers increase compare with the use of PEG as a pore forming agent, the specific surface area, total pore volume and average pore diameter of the PVDF porous fibers gradually increase with the increase of PVP dosage, while the average diameter of the porous fiber gradually decrease;3、Preparation of PVDF porous microspheres via electrospraying:With the increase of solution percentage concentration, the electrospraying products change from broken piece structure to a globular structure, then become a beaded structure, the specific surface area and total pore volume of PVDF porous microspheres decrease and the average diameter of the pores increase first and then decrease; With the increase of the proportion of DMF in the mixed solvent, the porous structure of PVDF porous microspheres decreases, and the specific surface area, total pore volume and the average diameter of the pores decrease gradually; With the increase of electrospraying voltage, the average diameter of PVDF porous microspheres increase first and then decrease, the diameter distribution range becomes wider; With the increase of the collecting distance, the average diameter of PVDF porous microspheres decrease and the diameter distribution become narrow gradually; With the increases of injection speed, the average diameter of PVDF porous microspheres increases gradually, and the diameter distribution increases gradually; PVDF porous microspheres with good spherical degree, and specific surface area is 6.96m2/g, the total pore volume is 0.035cm3/g, the average pore diameter is 19.08nm, and the average diameter is 3.59μm can be obtained when the mass percentage concentration of PVDF solution is 3wt%, the use of pure acetone as the solvent, the electrosprying voltage is 12kV, the injection speed is 4.0ml/h and the collecting distance is 15cm. |
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