## 1 Introduction
In order to produce the uniform formation of nanofibers, we investigated changing the electrospinningning conditions, such as the flow rate, voltage, and distance between the syringe tip and collector plate. In the case of a high-viscosity solution, the polymer solution and high applied voltage produce the formation of fiber without beads and thinner fibers. The surface tension is driven toward the formation of the beads and, thus, the reduced surface tension will favor the formation of the fibers without beads [20]. In addition, changing the polymer concentration may change the solution viscosity [21]. Furthermore, the droplet formation is due to the collapse of the capillary jet emitted by the surface tension [22]. For the polymer solution, the pattern of collapse of the capillary is dramatically changed. Instead of breaking rapidly, the filament and spraying droplets are stabilized and a stable bead structure is formed. The reason is that the dissolved polymer is transformed by the extensible flow of the jet into the solid fiber [23; 24; 25]. As the viscosity of the solution is increased, the beads and fiber diameter become larger and the shape of the beads also changes. When the applied voltage is increased, decreased surface tension makes the beads become smaller or gradually disappear, while the diameter of fibers also becomes smaller. Neutralization of the charge carried by the jet supports the formation of beads since the tension in the fibers depends on the net charge repulsion and the interaction of the net charge with the electric field. In this research, we analyzed the formation of the PAN nanofiber, thickness of the fiber, and the presence or absence of the beads by scanning electron microscope (SEM) images. This is the foundation to produce the PAN nanofiber under optimum conditions. In the manufacturing process, we used a commercially available heat roller to manufacture the PAN nanofiber air filter, via a lamination process using heat and pressure to seal the nanofiber paper between the plastic sheets. Normally, the heat, pressure, and adhesive are applied to bend the sheet of paper, but we used only the heat and pressure without the adhesive. The commercial heat rollers used in this research allow for controlled temperature and lamination speeds. The heat roller is composed of a pair of heated, rubber-covered rollers mounted on fixed axes, and a pair of stationary heated bars. The temperature signal for temperature control is provided by a surface thermocouple sliding on the metal core of one of the two heated rolls [26]. The PAN nanofiber air filter was manufactured in the lamination process. The non-woven fabric and nanofiber was manufactured by using heat and pressure applied to heat roller, respectively. PAN nanofiber air filter A was manufactured in a two-layerstructure (non-woven fabric, PAN nanofiber), and PAN nanofiber air filter B was manufactured as a sandwich structure (non-woven fabric, PAN nanofiber, non-woven fabric). As mentioned above, in order to produce the uniform formation of nanofiber materials used for air filter applications to protect sensitive components from harmful particulates and gaseous contaminants, we performed the electrospinning method as an efficient technique for fabricating polymer nanofibers. This research focused on optimizing the electrospinning conditions and manufacturing process to find the best method to manufacture nanofibers. The optimum conditions for manufacturing the PAN nanofiber were as follows: the solution sample including 1 g PAN and 10 mL DMF were physically stirred at a voltage of 10 kV, with a distance of 28 cm between the syringe tip and collector plate, and a flow rate of 0.3 mL/h. The experimental tests of fabricated nanofiber air filters in the laboratory, according to the British standard and the European standard, showed that they satisfied the criteria of high efficiency air filters.