## 3 Results and Discussion
### Mechanical Properties  
Finally, the mechanical properties of the materials prepared were examined using tensile measurements. Figure 6 shows a comparison of the samples containing different concentrations of coffee silverskin, which evidences a significant decrease of elongation at break of around 66.71% (WFF-20 ss) compared with the control WFF. All films with CS extracts demonstrated equivalent values of elongation at break (%) compared with the control WFF. Compared to the neat WFF, a significant increase in tensile stress at break was observed only in the WFF-2.5 ss film. The film presented a value of 4.73 \(\pm\) 0.24 MPa, an increase of up to 79% compared with the neat wheat flour film (Table 4). The WFF-5 ss and WFF-15 ss films exhibited similar values of tensile stress at break, higher than the control WFF, of up to 33.7%. Films with CS aqueous extracts showed a decrease in the tensile stress at break ranging from 54.9 to 64.0%. As shown in Figure 6, the Young's modulus of the WFF with coffee silverskin films was higher than that of the matrix, with similar values of up to 82.93%. The Young's modulus of the films with CS extracts was lower, between 43.9 and 52.5% for the WFF control film. It should be noted that the values obtained for Young's modulus may depend on how it is calculated. The highest value is obtained when it is estimated from the slope of the initial part of the load/extension curve. The values gradually decrease when it is calculated from the secant at an increased strain level. For rubbery polymers and crosslinked elastomers, often the so-called M100 value is calculated, which is the value of the stress at 100% extension (i.e., strain = 1). In this study, the first method was followed since in some of the samples, the tensile strain did not reach 100%. From the statistical analysis (Table 4), it was clear that the tensile strain at break was different for all composites with CS particles, whereas no significant difference was observed when CS aqueous extracts were used. Therefore, coffee silverskin particles as an additive to the WFF matrix led to higher tensile stress, and Young's Modulus values and CS aqueous extracts did not affect the elongation values. Figure 5: Antioxidant activity of the WFF-based biocomposites with coffee silverskin particles and extracts at time steps of 1, 2, 3, 4, 5, 6, and 24 h. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Tensile Strain at** & **Tensile Stress at** & **Young’s Modulus** \\  & **Break (\%)** & **Break (MPa)** & **(MPa)** \\ \hline WFF Control & 118.97 \(\pm\) 6.30 \({}^{\text{a}}\) & 2.64 \(\pm\) 0.13 \({}^{\text{a}}\) & 41.22 \(\pm\) 4.48 \({}^{\text{a}}\) \\ WFF-2.55s & 104.16 \(\pm\) 4.01 \({}^{\text{b}}\) & 4.73 \(\pm\) 0.24 \({}^{\text{b}}\) & 74.80 \(\pm\) 0.71 \({}^{\text{b}}\) \\ WFF-55s & 96.59 \(\pm\) 1.37 \({}^{\text{c}}\) & 3.53 \(\pm\) 0.02 \({}^{\text{c}}\) & 74.02 \(\pm\) 1.21 \({}^{\text{b}}\) \\ WFF-10 ss & 74.95 \(\pm\) 2.90 \({}^{\text{d}}\) & 2.28 \(\pm\) 0.21 \({}^{\text{a}}\) & 66.52 \(\pm\) 1.42 \({}^{\text{c}}\) \\ WFF-155s & 66.18 \(\pm\) 1.4 \({}^{\text{e}}\) & 3.53 \(\pm\) 0.12 \({}^{\text{c}}\) & 69.48 \(\pm\) 1.51 \({}^{\text{c}}\) \\ WFF-20 ss & 39.61 \(\pm\) 2.90 \({}^{\text{f}}\) & 2.82 \(\pm\) 0.18 \({}^{\text{a}}\) & 67.37 \(\pm\) 4.31 \({}^{\text{c}}\) \\ WFF-1\%A & 119.56 \(\pm\) 8.61 \({}^{\text{a}}\) & 1.16 \(\pm\) 0.19 \({}^{\text{d}}\) & 12.17 \(\pm\) 0.83 \({}^{\text{d}}\) \\ WFF-2\%A & 118.15 \(\pm\) 7.79 \({}^{\text{a}}\) & 0.95 \(\pm\) 0.01 \({}^{\text{e}}\) & 13.33 \(\pm\) 0.99 \({}^{\text{d}}\) \\ WFF-1\%B & 121.33 \(\pm\) 0.12 \({}^{\text{a}}\) & 0.99 \(\pm\) 0.05 \({}^{\text{d},e,f}\) & 22.63 \(\pm\) 3.22 \({}^{\text{e}}\) \\ WFF-2\%B & 120.61 \(\pm\) 11.09 \({}^{\text{a}}\) & 1.19 \(\pm\) 0.21 \({}^{\text{d},f}\) & 17.04 \(\pm\) 0.90 \({}^{\text{f}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Tensile strain at break (%), tensile stress at break (MPa), and Young’s modulus (MPa) of all prepared WFF biocomposites with coffee silverskin particles and extracts.