Electrospun Polymer Naofibers

Because of the very small diameters, a high specific surface area per unit mass and a high ratio of surface area to volume, nanofibers have manifested many special performances. And these fibers are of considerable interests for various kinds of application such as adsorption, filtration, protection and biological medicine. The technologies for the preparation of Polymer nanofibers include electrospinning, sea-island model spinning, catalyzed extrusion polymerization, and molecular spinneret spinning etc. Electrospinning is the focus way recently and has demonstrated a large potential.Electrospinning origins from that electrically charged fluid is forced jets in the high voltage electrostatic field. Electrospinning occurs when the electrical forces at the surface of a polymer solution or melt overcome the surface tension and cause an electrically charged jet to be ejected. When the jet dries or solidified, an electrically charged fiber remains. This charged fiber can be directed or accelerated by electrical forces and then collected in mats or other useful geometrical forms. The diameters of electrospun fibers are in the range of tens of nanometers to several micrometers.In this paper, Polyacrylonitrile (PAN) Nanofibers are made by electrospinning PAN/dimethylformamide(DMF) andPAN/dimethylacetamide(DMAC) with adjusting the main process parameters including electrostatic voltage(20 ~ 50KV), sprinkler aperture(0.5 ~ 0.8mm), collection distance(15 ~ 25cm), solution concentration(6 Wt%-14 Wt%). And the diameters of nanofibers are200 to l000nm. The process parameters are analyzed detailedly, which are important to the diameters and forms of nanoflbers. And the results demonstrate the electrostatic voltage and solution concentrate are determinant to the diameters of nanoflbers, and restrict the adjustment of other process parameters. On the other hand, the collection on a rotating cylinder is helpful to the process of electrospinning, and it is furthersome to get the ordered mats, otherwise, because the velocity of cylinder rotating is far less than that of nanofiber depositing, the rotation of cylinder has not the function of drawing. Also, the PAN mats are handed with heat treatment, preoxidation, carbonization. The heat treatment can enhance the strength of nanoflbers, and the mats deposited on the cylinder have luster by preoxidation and the diameter of nanofiber minish greatly after carbonization.Poly(m-phenylene-isophthalamide) (MPIA), poly(p-phenylene and 4,4'-diphenyl ether terephthalamide) (DPETA) etc nanoflbers are electrospun, and the different diameters of different polymers nanoflbers are described. The result is related with different molecular chains, and the structures of molecular chain decide the diameter ranges of electrospun fibers.The blend solutions of PAN & Second Cellulose Acetate (SCA) are electrospun to get synthetic fabrics. When the synthetic fabrics are washed in acetone, the pits can be showed in the surface of PAN nanoflbers. And the SEM pictures of the synthetic fibrics vary with the different proportion of PAN & SCA. When the proportion is 50:50, PAN and SCA shape into nanoflbers severally. Then when the contents of SCA are decreased, SCA are dispersed into PAN nanoflbers.According to the observations of experiments and the knowledge of electrostatic spray, the process of electrospinning polymer fibers isanalyzed. Primitively, the Taylor tape is shaped when the polymer solution conies out from the sprinkler, then the Taylor tape is elongated with the spray of instabilities, and the jets form solidified nanofibers gradually. As for as the shaping principle of nanofibers, we display two possibilities, which are split & thinning of jet and single thinning of jet. According to the analysis of jet single thinning, which is presented by Reneker etc, we educe a expression to calculate the velocity of nanofiber depositing to the collector, but the velocity range is very different from the reported result. On this ground, we assume the possibility of jet splitting.