Process - Structure – Property Relationships of Electrospun Nano Fibers

Electrospinning is a process by which fibers with diameters as small as 15 nanometers are produced when a polymer solution is accelerated from a capillary towards a grounded target by an electric field. An investigation on the electrospinning process and the effect of its process variables on orientation, crystallinity, microstructure and mechanical properties of the fibers produced are made. Nylon 6, nylon 66 fibers and their blends from a solution of formic acid were produced on a stationary copper target as well as on a metal disc rotating at discrete variable speeds. The solution concentration of the polymers, distance of the target from the syringe, the voltage applied and concentration of moisture were varied and their effect on the structure, morphology and properties were studied using scanning electron microscopy, dynamic mechanical analysis, fourier transform infrared spectroscopy, wide angle x-ray diffraction and density gradient column. This electrospinning process was used to produce PA66 fibers as small as 15 nm. The fibers were produced by electrospinning process only if the applied voltage is above a given limiting value. The diameter of the fiber obtained varied with the solution concentration, which in turn depends on solution charge density, type of polymer, and the solvent used. The diameter of nylon 66 fibers under conditions studied here does not depend on the target distance from the tip of syringe and the voltage applied. The amount of fibers spun by electrospinning process increases with the applied voltage. The orientation of fibers can be increased by collecting the fiber in a rotating wheel or annealing the fibers at high temperature and load. The fiber and molecular orientations and tensile modulus of electrospun nylon 6,6 fibers increase with orienatation of fibers. Poly(ethylene terepthalate) from a solution in trifluoroacetic acid and polystyrene/poly(methyl methacrylate) from tetrahydrofuran were also spun at a stationary target. A membrane like structure observed on spinning nylon 6 urged us to v study the effect of moisture content on morphology and mechanical properties of fibers. The preliminary results show better processability of polymers spun from acidic solutions than from organic solvents. Therefore an attempt has also been made to increase the conductivity of the organic solvents like THF by addition of soluble salts and hence improve the electrospinning capabilities of polystyrene and PMMA in THF. The information available in the literature was considered together with the experimental results to determine the effect of process variables on the nano sized polymer fibers spun.