## 3 Results and Discussion
### Mechanical Properties  
The measured mechanical properties are reported in Figure 4. As depicted, the addition of CNPs strongly influences both the tensile strength (MPa) and the elongation at break (%) of starch-PVA films. In detail, the tensile strength increased from 35 MPa for the control film sample to 47 MPa for films loaded with 5% CNPs, suggesting good interphase between CNPs and the starch-PVA matrix due to the compatibility between the chitosan and starch-PVA polymeric structures. This is likely owing to the nanofillers' entanglement and the development of the hydrogen bonding arrangement [24; 35; 36]. The ultimate tensile strength enhancement is associated with the crystallinity degree increase with the CNP amount, as evidenced by the XRD (Figure 3) and DSC (Table 1) data. As expected, the EAB of nanocomposite films decreased with the CNP loading amount: for example, starch-PVA films containing 5% CNPs presented 40% lower EAB than the control films. The decrease in EAB of the films is a result of the reduction in flexibility of the films. The decrease in free voids between polymer chains is due to an increase in intermolecular chains and a reduction in the consistency of the polymer matrix due to the presence of NPs [22; 31]. The same trend was highlighted by [PERSON] et al. [26] in the case of a plasticized starch (PS)-based film loaded with different amounts of CNPs (1, 2, 3, and 4%). Similarly, [PERSON] et al. [28] evaluated the influence of the CNPs' diameter size on the mechanical properties of modified cellulose films. In agreement, they reported that the addition of CNPs with an average diameter of 110-221 nm resulted in an increase in the films' TS and a decrease in the EAB, whereas, on the other hand, the addition of CNPs with a particle size of 85 nm increased both the TS and EAB of the films. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Glass Transition Temperature (\({}^{\circ}\)C)** & **Melting Enthalpy (J g-1)** & **Melting Temperature (\({}^{\circ}\)C)** \\ \hline \hline Starch-PVA 40:60 (SP) & 146.0 \(\pm\) 2.2 \({}^{\text{a}}\) & 31.3 \(\pm\) 0.7 \({}^{\text{c}}\) & 180.2 \(\pm\) 1.9 \({}^{\text{a}}\) \\ \hline SP+1\% CNPs & 141.2 \(\pm\) 1.5 \({}^{\text{b}}\) & 32.1 \(\pm\) 0.9 \({}^{\text{c}}\) & 184.9 \(\pm\) 2.6 \({}^{\text{a}}\) \\ \hline SP+3\% CNPs & 135.1 \(\pm\) 2.7 \({}^{\text{c}}\) & 36.6 \(\pm\) 1.6 \({}^{\text{b}}\) & 176.6 \(\pm\) 1.5 \({}^{\text{b}}\) \\ \hline SP+5\% CNPs & 130.5 \(\pm\) 3.0 \({}^{\text{c}}\) & 41.5 \(\pm\) 1.1 \({}^{\text{a}}\) & 173.9 \(\pm\) 1.2 \({}^{\text{b}}\) \\ \hline \hline \end{tabular}  
* Starch-PVA 40:60 (or SP as control film sample), starch-PVA loaded with 1% CNPs (SP+1% CNPs), starch-PVA film loaded with 3% CNPs (SP+3% CNPs), and starch-PVA film loaded with 5% CNPs (SP+5% CNPs). Results are presented as the mean \(\pm\) standard deviation. Different letters in each column indicate statistically significant differences at \(p\) < 0.05.  
\end{table} 
Table 1: Thermal properties of starch-PVA-based films. As expected, the EAB of nanocomposite films decreased with the CNP loading amount: for example, starch-PVA films containing 5% CNPs presented 40% lower EAB than the control films. The decrease in EAB of the films is a result of the reduction in flexibility of the films. The decrease in free voids between polymer chains is due to an increase in intermolecular chains and a reduction in the consistency of the polymer matrix due to the presence of NPs [22; 31]. The same trend was highlighted by [PERSON] et al. [26] in the case of a plasticized starch (PS)-based film loaded with different amounts of CNPs (1, 2, 3, and 4%). Similarly, [PERSON] et al. [28] evaluated the influence of the CNPs' diameter size on the mechanical properties of modified cellulose films.