## 3 Results and Discussion
### Improvement of Electrical Conductivity by Additives  
The current can be increased by adding polar additives, such as AZ, QC, OA, GA, and CH. Figure 4 shows the change in conductance at 200 \({}^{\circ}\)C when various amounts of  
Figure 3: Structures of quercetin hydrate (QC), oleic acid (OA), alizarin (AZ), (+)-catechin hydrate (CH), and gallic acid monohydrate (GA).  
Figure 2: Structure of polycaprolactone (PCL).  
additives were introduced into the molten PCL. To analyze the change in the conductance of the solution, LSV data were acquired in the potential range of 0-1 V at a 0.1 V/s scan rate to construct the \(I\)-\(V\) plot. During the measurement, the additives were introduced at a ratio (wt%) up to the solubility limit, which is the maximum limit at which the additive and PCL solutions can be homogeneously mixed. The solubility limits for each additive were 1 wt% AZ, 4 wt% QC, 7 wt% GA, 10% CH, and 10% OA. The slope of the obtained \(I\)-\(V\) plot represents the conductance of the solution. As shown in Figure 4, the slope increased with all additives. Thus, the conductance of the solution increased. In general, the conductance of a solution is determined by the charge carrier, the presence of ions, ion mobility, and polarity of the solvent. Because the polar additives used in the experiment contribute to increasing the number of ions and the polarity of the solution, the conductance of the solution increases.  
To compare the effects of the type of additive, we converted the slope of the \(I\)-\(V\) plot of the PCL solution (obtained in Figure 4) into the electrical conductivity (Figure 5). Pure PCL solution exhibited a conductance of 2 pS at the applied temperature (200 \({}^{\circ}\)C). After introducing various additives into the solution, the conductance increased as the content of each additive increased. The numerical values, which are measures of the conductance change according to the type and amount of additive, can be found in the Supplementary Materials, Tables S2-S6. The difference in the degree of conductance improvement for each additive is due to the difference in the size and number of ions generated, and the degree of polarity of the additive, depending on the amount and type of additive used. Because the radius of the generated ions is small and the number of ions increased, the charge density is increased, and thus, the electric conductivity increased, owing to the influence of the external electric field [37; 38; 39].  
First, when 1 wt% AZ was added, the conductance of the PCL solution increased to 85 pS, which is 43 times higher than that of pure PCL. Similarly, the conductance of the solution increased to 86.8 pS with the addition of 10 wt% CH, and up to 120.5 pS with the addition of 4 wt% QC, indicating a 45-fold and 60-fold improvement in conductance com  
Figure 4: Effect of wt% and type of additives introduced into PCL on current at 200 \({}^{\circ}\)C. (**a**) AZ, (**b**) QC, (**c**) OA, (**d**) GA, (**e**) CH.  
pared to that of the pure PCL solution, respectively. Among the analyzed non-toxic natural additives, the additive with the least improvement in conductance was OA (10 wt%). With the addition of OA, the conductance of the solution increased to 11 pS, i.e., approximately six-fold. GA addition at 7 wt.% led to a surprisingly high improvement rate. The conductance of the PCL polymer solution improved to 168 pS, which is an 81-fold increase. This means that when the additives are introduced up to the solubility limit, most of the current can flow in the GA used as the additive. Therefore, if GA is added during melt electrospinningning of PCL, it is expected that a stronger elongation force can be applied to the jet compared to the force that can be applied with the other additives, and the finest fibers can be formed during spinning.