## 3 Results and Discussion
### Properties of the Nanocomposite Films
#### 3.2.3 Mechanical Properties  
The thickness of the neat gelatin film was 51.8 \(\pm\) 0.9 \(\upmu\)m, which slightly decreased when 0.5 wt % of CuSNP was added. It increased somewhat with a higher amount of CuSNP (1.0 and 2.0 wt %) (Table 3); however, the change was not statistically significantly (\(p>0.05\)).  
Figure 3: FESEM micrographs (surface and cross-section) of Gel/CuSNP films.  
On the other hand, the addition of CuSNP significantly influenced the mechanical properties of the gelatin film (Table 3). The tensile strength (TS) of gelatin film was 45.0 \(\pm\) 2.7 MPa, similar to the earlier reported data [40,41]. The TS of the gelatin film significantly increased to 58.1 \(\pm\) 2.4 MPa when 0.5 wt % of CuSNP was included and further improved to 65.1 \(\pm\) 2.4 MPa at 1.0 wt % of CuSNP, then slightly declined to 63.4 \(\pm\) 3.8 MPa at 2.0 wt % of CuSNP. The reduced TS of the 2 wt % CuSNP-added film compared to the 1 wt % of CuSNP-added film was due to the accumulation of particles at the high content as perceived in the surface microstructure (Figure 3). Similar to the TS, the elastic modulus (EM) (stiffness) of the gelatin film was also noticeably increased, adding CuSNP.  
Figure 4: Structure of gelatin (**a**) and FTIR spectra (**b**) of Gel/CuSNP films.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Films** & **Thickness (\(\mu\)m)** & **TS (MPa)** & **EB (\%)** & **EM (GPa)** & **WCA (Deg.)** & **WVP (\(\times\) 10\({}^{-9}\)** \\  & & & & & & **g-m/m\({}^{2}\):Pa-s)** \\ \hline Gelatin & 51.8 \(\pm\) 0.9 ab & 45.0 \(\pm\) 2.7 a & 8.6 \(\pm\) 1.7 b & 1.5 \(\pm\) 0.04 a & 63.4 \(\pm\) 0.8 a & 2.26 \(\pm\) 0.37 b \\ Gel/CuS\({}^{0.5}\) & 49.8 \(\pm\) 0.3 a & 58.1 \(\pm\) 2.4 b & 6.0 \(\pm\) 0.1 a & 2.3 \(\pm\) 0.04 b & 63.2 \(\pm\) 0.5 a & 1.98 \(\pm\) 0.03 ab \\ Gel/CuS\({}^{1.0}\) & 55.6 \(\pm\) 4.3 b & 65.1 \(\pm\) 2.4 c & 7.2 \(\pm\) 0.4 ab & 2.3 \(\pm\) 0.12 b & 61.1 \(\pm\) 1.4 a & 1.84 \(\pm\) 0.09 ab \\ Gel/CuS\({}^{2.0}\) & 56.5 \(\pm\) 3.4 b & 63.4 \(\pm\) 3.8 c & 6.7 \(\pm\) 0.2 a & 2.2 \(\pm\) 0.05 b & 61.4 \(\pm\) 1.8 a & 1.64 \(\pm\) 0.14 a \\ \hline \hline \end{tabular}  
* The matching superscript letters in each column indicate that they are not significantly dissimilar (\(p\) > 0.05) from [PERSON]’s multiple range tests.  
\end{table}
Table 3: Mechanical properties, hydrophobicity, and water vapor permeability of control and gelatin/CuSNP films.  
On the contrary, the elongation at break (EB) (flexibility) of the gelatin film was reduced significantly (\(p<0.05\)) by adding CuSNP; however, there was no significant difference in flexibility between the gelatin/CuSNP composite films. The improved strength and reduced flexibility of gelatin films by blending CuSNP are most likely owing to the increased molecular interaction between the nanofiller and polymer matrix at the interface, strengthening the nanocomposite and reducing the mobility of polymer chains. A similar result of CuSNP has been detected in other films, such as agar/CuSNP and carrageenanan/CuSNP nanocomposite films [24]. Meanwhile, the mechanical properties of gelatin-based films seem to vary depending on the class of nanoparticles added. For example, the gelatin film's strength increased when a low concentration of TiO\({}_{2}\) was added [19; 20], but the physical strength decreased when ZnONP and AgNP were added [17].