## 3 Results and Discussion
### Preparation of Electrospun Pectin-Based Fibers
The solution properties were determined to better understand the morphologies of the ultrathin pectin-based fibers in the attained electrospun mats. The values of viscosity, surface tension, and conductivity of the fiber-forming solutions are also given in Table 2. For the non-plasticized solutions, that is, S1-S4, viscosity of the pectin-based solutions increased significantly when the amount of PEO\({}_{2000}\) was increased. One can observe that the addition of plasticizers did not create any significant difference in the solution viscosity. Even when the content of glycerol or PEG\({}_{900}\) was increased to 3 wt%, the solution viscosity did not change considerably, showing a value around 6000-6400 cP. The surface tension slightly increased from approximately 29 mN/m to values in the range of 31-33 mN/m when the PEO\({}_{2000}\) content was increased above 0.5 wt%. It was not observed a clear correlation between the plasticizer content and the surface tension of pectin-based solutions. It can also be observed that, due to the inherent polyelectrolyte nature of pectin [60], its aqueous solutions were highly conductive, showing values in the 6-8 \(\upmu\)S.cm range. However, the conductivity values decreased up to values close to 4 \(\upmu\)S.cm when the PEO\({}_{2000}\) content was increased and, particularly, when the plasticizers were added since the amount of pectin in the solution was reduced. Therefore, the present results suggest that the fiber formation was attained due to a combined effect of viscosity increase and conductivity decrease. The optimal values were particularly attained in the range of -5500-6500 cP and -5-6 \(\upmu\)S.cm of viscosity and conductivity, respectively. Therefore, moderate-to-high viscosities in combination with relatively low conductivities tended to produce the fibers with the most optimal morphology, while the effect of surface tension was negligible. As previously indicated in other works describing the role of solution properties in the electrospinningnability of biopolymers [32], it was difficult to elucidate the effect of a single property without considering the impact of the other ones. In relation to the plasticizers, one can observe that the diameters of the fibers varied from 156 \(\pm\) 33 nm to 329 \(\pm\) 42 nm, which could be related to differences in the solution properties described above. Significantly thicker fibers were attained with the increase of the PEO\({}_{2000}\) content (from S2 to S4) for the non-plasticized samples since the viscosity of these solutions was increased with the PEO\({}_{2000}\) content [49]. Also, the incorporation of glycerol to the PEO\({}_{2000}\) containing fibers resulted in significantly thicker fibers. This increase in the fiber diameter can be related to the increase in the solution viscosity. As shown in Table 2, S3 showed a viscosity of 5950 cP and it yielded fibers with average diameter of 186 \(\pm\) 32 nm, whereas fibers with an average diameter of 329 \(\pm\) 42 nm was attained in S7 with a viscosity of 6440 cP. This observation can be ascribed to the plasticizing effect of glycerol, which favored the molecular entanglements of the pectin chains by reducing their intermolecular interaction. The latter effect is based on the fact that intermolecular H-bonds of pectin can be substituted by glycerol-pectin H-bonds and covalent esters, thus the attraction between pectin molecules is reduced [29]. A similar phenomenon was also reported by [PERSON] et al. [40] where glycerol-containing solutions resulted in pectin-based fibers with higher diameters than those obtained from solutions using dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) as co-solvents. Also, if one compares the solutions containing 2.5 wt% of plasticizer, which were labelled as S5 and S8, the glycerol-containing ones yielded fibers with an average diameter of 272 \(\pm\) 43 nm, while the solutions with PEG\({}_{900}\) produced fibers in the range of 189 \(\pm\) 40 nm.