## 3 Results and Discussion
### Application of Pectin-Based Electrospun Film in Multilayers  
The electrospun pectin film was integrated as an inner layer into two electrospun PHBV films, which were prepared as described previously by [PERSON] et al. [51]. The objective of this multilayer was to apply the here-prepared pectin film, which was prepared by the annealing of fibers from S7 solution, as a barrier interlayer that was protected from humidity by two external electrospun layers of PHBV, a bio-based and biodegradable hydrophobic polyester. The whole multilayer structure was formed by electrospinning and subsequent annealing in order to achieve a high adhesion between the layers. A cast film of pectin was also applied in the same conditions for comparison purposes. Figure 9 shows the visual aspect of the electrospun multilayer films to evaluate their contact transparency. The effect of the inner pectin-based interlayer on the color coordinates L*a*b* and \(\Delta\)E* of the electrospun PHBV films are shown in Table 5. One can observe that all the here-prepared multilayer films presented a good contact transparency. However, a slightly yellowish was developed when the pectin layer was incorporated, particularly for the material obtained by electrospinning and annealing. In particular, the b* values of the PHBV/PHBV multilayer increased from \(-0.36\) to \(4.95\) and \(0.83\) for the PHBV/solvent-casted pectin/PHBV and PHBV/electrospun pectin/PHBV multilayer films, respectively. Furthermore, in the case of the PHBV/electrospun pectin/PHBV multilayer, the slight increase in the \begin{table}
\begin{tabular}{c c} \hline \hline
**Wavenumber (cm\({}^{-1}\))** & **Chemical Group** \\ \hline
1741 & C–H stretching \\
1672 & Amide I \\
1595 & Amide II \\
1132 & C–C \\
1070 & C–O \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Band attribution of the main peaks observed in the Fourier transform infrared spectroscopy (FTIR) spectra of the pectin-based materials. Figure 8: Fourier transform infrared spectroscopy (FTIR) spectra, from bottom to top, of pectin powder, glycerol, and polyethylene oxide 2000 (PEO\({}_{2000}\)), and electrospun fibers and film obtained from S7. a* value suggest that the films became brown. This effect can be related to the original color of the electrospun pectin layers, which was shown in previous Figure 7 and their color values are gathered in Table 5. Therefore, both pectin interlayers generated multilayer films in which an observer can notice different colors (\(\Delta\)E*\({}_{\text{ab}}\) \(\geq\) 5). In particular, the \(\Delta\)E* values for the PHBV/solvent-casted and PHBV/electrospun pectin/PHBV multilayer films were 9.60 and 11.48, respectively. Additionally, it is worthy to mention that the neat PHBV/PHBV films showed lower transparency than the PHBV monolayers films that were reported in our previous research study [56]. This can be related to possible air entrapment between both PHBV layers during annealing. The cross-sectional SEM images of the obtained multilayer structures are displayed in Figure 10. One can observe in Figure 10a that the bilayer control of PHBV/PHBV formed a continuous structure in which both layers could not be discerned. In relation to the PHBV/pectin/PHBV multilayers, it can be seen that the structure obtained from the electrospun-based pectin film, shown in Figure 10b, presented higher adhesion between layers. However, the multilayer structure based on the cast film of pectin, seen in Figure 10c, easily delaminated during the preparation and observation by SEM. Therefore, multilayer assemblies with a high interlayer adhesion were successfully attained by combining electrospinning and annealing treatments. This effect has been recently attributed to the high aspect ratio of the electrospun fibers, which coalesce during annealing and thus highly adhere to the material substrate [53].