| During the development of fiber industry, microfiber is an important goal. With the rapid development of nanoscience and technology, the preparation and applications of nanofibers become the hot field in research. In order to make fibers with diameters between submicrometer and nanometer, electrospinning is the most important and viable method, in which the microfibers are forming from polymer solutions or melts with the help of high voltage electric field. These electrospun fibers or mats have high surface area and porosity, as well as small diameters. They have enormous potential applications in wound dressing, filtration, protective clothing, tissue scaffolds, drug delivery system, high-performance cells, catalysis, and sensors. The hollow carbon microfibers (HCMFs) prepared by coaxial electrospinning not only have all the characters of the carbon fibers prepared by CVD method, but also have the same structure, capability and application with carbon nanotubes. Many potential applications have been proposed for HCMFs, including the anode of lithium ion battery, double lay capacitor electrode, high effective sorbent and structure strengthen materials, based on their high intensity and module, thermal capability stability, chemical active and electric conductivity.In this paper, using coaxial electrospinning technology, the skin-core composite microfibers were prepared by selecting different spinning solutions and process parameters. Through the appropriate soak, pre-oxidation and carbonization process, the carbon microfibers with hollow structure were gained ultimately.In this paper, by improving the electrospinning devices, we designed a coaxial electrospinning devices and spinning process to determine a viable method of preparation of hollow microfiber. A series of tests were on inner fluid and outer fluid, such as solution viscosity, conductivity, and surface tension, and so on. Using polyacrylonitrile(PAN)/DMF and polyvinylpyrrolidone(PVP)/DMF as outer fluid and inner fluid respectively, PAN/PVP skin-core microfibers was prepared by coaxial electrospinning. The PAN/PVP skin-core microfibers were soaked into the water to remove the PVP core layer component, and then through the pre-oxidation and carbonization process hollow carbon microfibers were prepared.In this paper, in order to determine of optimal process parameters to prepare the coaxial electrospun hollow microfibers, the solution properties, inner and outer capillary diameter, voltage, receiving distance, outer fluid and inner fluid velocity ratio were discussed. The influence of these parameters on the electrospun fibers morphology was discussed, and the optimal process parameters were found finally. When the outer fluid PAN_b concentration of 16%, the inner fluid PVP concentration of 30%, inside and outside needle within the aperture beingΦ_I= 0.8mm andΦ_O=1.6mm respectively, voltage 11kV, receiving distance 15cm, 50μl/min outer and 25μl/min inner fluid velocity, the skin-core composite microfibers were prepared successfully. After removing core layer, regular hollow structure of microfibers can be observed by scanning electron microscopy tests.The PAN/PVP skin-core fibers dried in blast drying box after PVP removed by soaking in water, and then placed in muffle furnace for pre-oxidation. Effects of the temperature and heating rate on the structure and property of pre-oxidation web were discussed in this paper. When the pre-oxidation heating rate was 5℃/ min and pre-oxidation temperature was 250℃, the obtained felt had the fully pre-oxidation treatment.The morphology of electrospun microfibers, pre-oxidized microfibers and carbon microfibers were studied by scanning electron microscope (SEM). The changes of chemical composition and crystalline morphology of electrospun microfibers, pre-oxidized microfibers and carbon microfibers were performed by X-ray diffractometry and infrared spectroscopy respectively.
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