Fundamental Investigations on Electrospun Fibers

摘要

The results of and conclusions based on a number of distinct studies designed to probe the structure and morphology of electrospun fibers are reported. All fibers were formed using a conventional needle electrospinning apparatus. Electrospun poly caprolactone/acetone solutions formed beads at low solution concentration, but the beads disappeared at high solution concentration and viscosity. Histograms of fiber diameter were constructed for polyacrylonitrile fiber formed from dimethylformamide solutions. The fiber diameter distribution appears to be log normal. Solution viscosity had a much greater effect on fiber diameter than did applied voltage, showing the large role viscous forces play and the surprisingly small role of electrostatic forces in attenuation. The birefringence of poly (ethylene oxide fibers ranged from 0.001 for large fibers to 0.020 for midsize fibers, showing that molecular orientation in electrospun fibers is disappointingly low. Tenacity of 0.14 denier fibers was about 2.9 g/d and elongation-to-break about 190%, consistent with the low molecular orientation. Differential scanning calorimetry on electrospun polyacrylonitrile fibers run at high heating rates showed the presence of a weak endotherm, indicating that fibers are semicrystalline, as anticipated. The inescapable conclusion is that electrospun fibers generally have low molecular orientation and poor mechanical properties. Either the fiber properties never develop, or they are quickly lost due to relaxation processes.