## 3 Results
### Mechanical Properties  
The mechanical performances of the zein films were evaluated through the characterization of tensile strength, elongation at break, and Young's modulus values. The films obtained from electrospinning showed evident brittleness in handling, a fact confirmed by other authors who have investigated how to improve the mechanical properties of electrospun materials deriving from natural proteins, for example by using polymeric blends [47]. For this reason, the samples obtained by electrospinning were not subjected to mechanical tests. Instead, the mechanical properties were evaluated for continuous samples produced through the other two techniques. The results of the tests conducted on the samples produced by solvent casting are shown in Table 3. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Measurement** & **SCG 0\%** & **SCG 15\%** & **SCG 20\%** & **SCG 35\%** & **SCG 45\%** \\ \hline OPC (m\({}_{\text{STP}}\)\({}^{3}\) m/(m\({}^{2}\) s Pa) \(\times\) 10\({}^{20}\) & 470 \(\pm\) 70 & 200 \(\pm\) 30 & 5.8 \(\pm\) 0.9 & 1.4 \(\pm\) 0.2 & 4.9 \(\pm\) 0.7 \\ OTR (m\({}_{\text{STP}}\)\({}^{3}\)/m\({}^{2}\) s) \(\times\) 10\({}^{11}\) & 940 \(\pm\) 122 & 480 \(\pm\) 62 & 20 \(\pm\) 2.6 & 4.7 \(\pm\) 0.6 & 16 \(\pm\) 2 \\ OTR (cc/m\({}^{2}\) day) & 202 \(\pm\) 26 & 86 \(\pm\) 11 & 25 \(\pm\) 3 & 6 \(\pm\) 0.8 & 21 \(\pm\) 3 \\ \hline \end{tabular}
\begin{tabular}{c c c c c} Units\({}^{\prime}\) conversion: 1 m\({}_{\text{STP}}\)\({}^{3}\) m/(m\({}^{2}\) s Pa) = 4.4 \(\times\) 10\({}^{3}\) mol/(m s Pa), 1 m\({}_{\text{STP}}\)\({}^{3}\)/s = 4.4 \(\times\) 10\({}^{3}\) mol/(m\({}^{2}\) s) = 2.2 \(\times\) 10\({}^{10}\) cc/(m\({}^{2}\) day). \\ \end{tabular}
\end{table} 
Table 2: OPC and OTR measurements results for different packaging films at different SCG concentration, from 0% to 45%. In particular, all samples had a tensile strength higher than those reported in other works and higher than the limit set for packaging materials equal to 3.5 MPa [48,49]. Moreover, all the films presented poor elongation at break and high Young's modulus values. It is interesting to note that the presence of the SCG extract did not particularly affect the results. Only at 45% \(w\)/\(w\) of SCG extract were the mechanical properties generally worse, in fact the elongation at break was lower, indicating greater fragility of the samples, while the Young's modulus value was higher, indicating greater rigidity of the material. The reason can be attributed to the presence of a higher dry solid fraction of extract inside the samples, compared to the extract loaded in lower concentrations, which involves the addition of irregularities in the material with a consequent decrease in mechanical performance. This brittleness, which is known to be the greatest intrinsic weakness in vegetable proteins, could also be attributed to the amount of glycerol used. In fact, it has been studied by [PERSON] et al., 2015, that glycerol can act both as an anti-plasticizer, worsening the mechanical properties and as a plasticizer, improving them depending on the quantity used [50]. Furthermore, as regards the films obtained by spin coating, the blank samples of zein were preliminarily compared with those produced by solvent casting, to investigate the influence of the production technique on the mechanical properties and it emerged that the spin coated samples did not meet the minimum requirements, having presented a tensile strength of 1.13 \(\pm\) 0.18 MPa, while the elongation at break was comparable with solvent castings 0.76 \(\pm\) 0.12% and the Young's modulus value was lower and equal to 152.05 \(\pm\) 16.76 MPa. These results are clearly different from those of the samples obtained by casting, and it could be because of the centrifugal force imparted by the rotation of the spin coater support on the arrangement of both polymer and plasticizer molecules.