Electrospinning process of polymer melts

Polypropylene and poly (ethylene naphthalate) were electrospun from the molten state in a vacuum and poly (caprolactone) (PCL) was successfully electrospun in air. Electrical charge was supplied by mean of a metal wire immersed in the molten polymer. Under the influence of external electric field, charges migrated through the melt to the surface. As the electric field strength was increased, a droplet of molten polymer started to deform from a semi-spherical into a conical shape due to the interaction between a surface tension and the Coulombic forces among surface charges. A semi-angle of the cone was in the range of 34 to 38 ± 2°, which was close to a prediction by Yarin. Above a critical field strength, a droplet of molten polymer was pulled out, trailed by a jet that became thin and soon broke. When the field strength was increased, a steady charged jet flowed toward the collecting plate. The jets were collected to an aluminum sheet maintained at an attractive electrical potential. The jet either solidified in flight or after it landed on the collector.; Electrospun fibers produced in vacuum had diameters that ranged from 300 nanometers to about 30 micrometers, while the diameters of the PCL fibers ranged from 400 nanometers to 30 micrometers. Varieties of fiber morphologies were observed, including flat fibers, coiled fibers, bent fibers and helical fibers.; SEM images showed that the molten charged jet developed electrically driven bending instabilities during the spinning process. The behavior of the charged PCL jet, observed with high frame rate video camera, during the electrospinning process can be categorized into 3 groups. (i) A straight charged jet that deformed via a buckling mechanism as it landed. (ii) A straight charged jet that developed the bending instability close to collecting plate. (iii) A charge jet that developed the bending instability in flight. Electric filed strength, temperature, molecular weight and gap distance between electrodes all played a role on the behavior of the jet and the fiber diameter.