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This work examines the effect of selected process parameters on the diameter of uniform and heterogeneous fibers (with and without bead-on-string structures) and the size of beads obtained during the electrospinning process. A 23 factorial design was performed to determine the influence of the following factors: electrical voltage, flow rate and dynamic viscosity of the poly(vinylpyrrolidone) ethanolic solution. Factorial design enables the analysis of the mathematical relationship between the chosen factors and the response with a minimum number of experiments. The factor having the most significant impact on the size of beaded fibers and beads was the solution viscosity, while the voltage had the greatest influence on the bead-free fiber diameter. The interactions between the studied factors were also analyzed. It was found that the presented method can be used for the design of an optimal and cost-effective electrospinning process, allowing the desired product to be obtained with expected features.

Electrospinning processes are commonly conducted with direct-current voltage (DCV) but the fibers can also be electrospun using a pulsed voltage (PV). Although this method has been used in other electrostatic processes, there is little research on its application in nanofibers production. In this work, the voltage was supplied to the polymer solution in pulses with a given amplitude, frequency, and duration. Experiments were performed with two polymers (polyvinylpyrrolidone and polylactide) using both DCV and PV. The shape of the liquid jet formed at the nozzle tip was observed and linked to the structure of the polymer mats, including the diameters of the electrospun fibers and the sizes and the concentrations of spherical elements. Some differences in products electrospun using DCV and PV were observed both for polyvinylpyrrolidone and polylactide. The parameter that most strongly influenced the examined properties of the polymer mats was the pulse frequency. Moreover, for polylactide the PV method eliminates polymer clogging, providing greater stability of the electrospinning and changes the distribution of fiber diameters into a bimodal one. In general, PV gives better control over fiber diameters and bead sizes because of the possibility of more precise electric charge delivery due to a lower effective voltage. Keywords: Electrospinning, Pulsed voltage, Polymer fibers, Meniscus, Droplet shape, Electrospinning jet