## 3 Results and Discussion
### Spectral Analysis  
The UV-Vis spectra of the films are shown in Figure 1. Analysis of the UV-Vis spectra of the PBS films showed clear differences in absorbance depending on the type and concentration of the extracts. The control PBS sample (without additives) and the sample modified with 0.01 g of Chl or scCO\({}_{2}\) extract per 1 g of PBS exhibited similar absorbance over the entire visible-light spectral range (300-800 nm), indicating a higher optical density or higher light absorption capacity compared to samples modified with 0.05 g extracts. The addition of 0.05 g Chl extract lowered the absorbance compared to that of the control and modified it with the lower-concentration extract samples. An even greater trend was observed for the PBS containing 0.05 g of scCO\({}_{2}\) extract. Overall, the use of the extracts led to a reduction in the optical permeability of the films, with the scCO\({}_{2}\) extract having a greater effect than the Chl extract. It is interesting to note that extracts at lower concentration led to an increase in absorbance in UV range, while the addition of a higher amount resulted in a decrease in absorbance in this range. These results suggest that modification of PBS with extracts may be useful in applications requiring controlled light transmission, such as UV-protective packaging. Similarly, [PERSON] et al. modified PVA films with sea buckthorn leaf extracts and observed shifts in their UV-Vis spectra depending on the concentration of the plant extract in the polymer matrix [22]. Figure 2 shows the FTIR spectra of the scCO\({}_{2}\) and Chl extracts from the sea buckthorn. The analysis of the FTIR spectra indicated the presence of characteristic functional groups in their chemical structures. The spectra of both extracts show intense bands in the range of 2800-3000 cm\({}^{-1}\), corresponding to the stretching vibrations of methyl groups (-CH\({}_{2}\) and -CH\({}_{3}\)) present in long-chain hydrocarbons or lipids. The scCO\({}_{2}\) extract exhibited \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Thickness (mm)** & **TS (MPa)** & **EB (\%)** \\ \hline PBS & 0.019 \(\pm\) 0.001 \({}^{\text{a}}\) & 6.16 \(\pm\) 1.70 \({}^{\text{b,c}}\) & 14.48 \(\pm\) 2.54 \({}^{\text{a}}\) \\ PBS-Chl 0.01 & 0.018 \(\pm\) 0.001 \({}^{\text{a}}\) & 6.86 \(\pm\) 2.23 \({}^{\text{c}}\) & 13.95 \(\pm\) 2.59 \({}^{\text{a}}\) \\ PBS-Chl 0.05 & 0.020 \(\pm\) 0.001 \({}^{\text{a}}\) & 3.95 \(\pm\) 1.26 \({}^{\text{a}}\) & 14.02 \(\pm\) 2.99 \({}^{\text{a}}\) \\ PBS-CO\({}_{2}\) 0.01 & 0.021 \(\pm\) 0.002 \({}^{\text{a}}\) & 5.93 \(\pm\) 1.34 \({}^{\text{a,b,c}}\) & 13.17 \(\pm\) 1.93 \({}^{\text{a}}\) \\ PBS-CO\({}_{2}\) 0.05 & 0.022 \(\pm\) 0.002 \({}^{\text{a}}\) & 4.15 \(\pm\) 0.61 \({}^{\text{a,b}}\) & 13.74 \(\pm\) 2.64 \({}^{\text{a}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Thickness and mechanical characteristics (tensile strength (TS) and elongation at break (EB)) of PBS films. noticeably stronger bands in this range, suggesting that it contained a higher amount of lipid compounds. In addition, an intense band associated with the presence of carbonyl groups (C=O), characteristic of esters or fatty acids, was identified in the range of 1700-1750 cm\({}^{-1}\), which was also more prominent in the scCO\({}_{2}\) extract. In the lower ranges (1000-1500 cm\({}^{-1}\)), bands corresponding to the vibrations of C-O and C-H bonds were present, indicating the presence of compounds, such as alcohols, esters, and phenols. The Chl extract showed more intense bands at lower frequencies (below 1000 cm\({}^{-1}\)), which may suggest differences in the composition of aromatic or polar compounds compared with the scCO\({}_{2}\) extract. These results indicate that the scCO\({}_{2}\) extract contains more lipid compounds and fatty acids, whereas the Chl extract may be richer in polar compounds. These results are similar to the FTIR spectra obtained for sea buckthorn extracts in other solvents [28]. Figure 3 shows the FTIR spectra of pure and modified PBS films.