## 3 Results and Discussion
### Thermophysical Characteristics of PHB-Cmitosan and PLA-Cmitosan Compositions
The DSC analysis of the PHB-chitosan compositions (Figure 2) shows that, in contrast to the initial PHB, the presence of chitosan and sorbed Fe\({}^{3+}\) ions in the compositions leads to the appearance of an additional small endo-peak with a temperature of 165 \({}^{\circ}\)C, which can be attributed to the melting of the imperfect form of PHB crystallites. At the same time, the degree of PHB crystallinity in the PHB-chitosan composition decreases to 18.9%, and in the PHB-chitosan compositions with sorbed Fe\({}^{3+}\) ions, it decreases to 21.3% compared to the initial PHB (Table 2). This indicates the amorphization of PHB in compositions with chitosan during their liquid-phase preparation by analogy with PLA. The thermal stability of PLA, PHB, and their compositions with chitosan has been studied using DSC. The onset temperature (T\({}_{\rm on}\)) of the thermal decomposition was determined according to the ISO 11357-1:2010-03 standard. The value of T\({}_{\rm on}\) has been defined as the calculated point of the intersection of the extrapolated baseline and the inflection tangent at the beginning of the degradation peak on the DSC curve. The data are shown in Figures 3 and 4 and in Table 3.  
From the DSC data presented in Figure 3, the influence of chitosan on the sharp decrease in the onset thermal degradation temperature (T\({}_{\rm on}\)) of the PLA-chitosan composition and PLA-chitosan composition containing sorbed Fe\({}^{3+}\) ions in contrast to original PLA: 237 \({}^{\circ}\)C, 244 \({}^{\circ}\)C and 332 \({}^{\circ}\)C, respectively, can be clearly seen. There is also a significant decrease (of approximately 100 \({}^{\circ}\)C) in the enthalpy peak (T\({}_{\rm max}\)) of the thermal decomposition of the PLA-chitosan and PLA-chitosan compositions containing absorbed Fe\({}^{3+}\) ions compared with the original PLA: 269 \({}^{\circ}\)C, 275 \({}^{\circ}\)C, and 372 \({}^{\circ}\)C, respectively (Table 2). At the same time, it is necessary to note the stabilizing effect of Fe\({}^{3+}\) ions on PLA-chitosan thermal decomposition, which is clearly manifested under the comparison of the values of the decomposition enthalpy (\(\Delta\)H\({}_{\rm d}\)) of PLA-chitosan and PLA-chitosan compositions containing absorbed Fe\({}^{3+}\) ions (Table 3). Figure 4 demonstrates the effect of the presence of chitosan on the thermal stability of PHB. However, unlike PLA compositions, the effect of chitosan on the decrease in T\({}_{\rm on}\) and T\({}_{\rm max}\) values for PHB-chitosan compositions is not so pronounced Thus, the value of T\({}_{\rm on}\) for PHB gradually decreases from 264 \({}^{\circ}\)C (PHB) to 255 \({}^{\circ}\)C (PHB-chitosan (50:50) wt. %) and 246 \({}^{\circ}\)C for the PHB-chitosan composition with sorbed Fe\({}^{3+}\) ions (Table 3). On the other hand, from the data presented in Table 2, the stabilizing factor of Fe\({}^{3+}\) ions in the process of PHB with chitosan thermal decompositions can be clearly observed. This is expressed in an increase in the values of T\({}_{\rm max}\) and \(\Delta\)H\({}_{\rm d}\) for the composition of PHB-chitosan with adsorbed Fe\({}^{3+}\) ions (278 \({}^{\circ}\)C and \(-\)687 J/g) in comparison with the analogous values of 268 \({}^{\circ}\)C and \(-\)584 J/g for the PHB-chitosan composition (Table 3). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample** & **T\({}_{\rm g^{\prime}}\)\({}^{\circ}\)C** & **T\({}_{\rm cc^{\prime}}\)\({}^{\circ}\)C** & \(\Delta\)H\({}_{\rm cc}\), J/g** & **T\({}_{\rm m^{\prime}}\)\({}^{\circ}\)C** & \(\Delta\)H\({}_{\rm m}\), J/g** & **\(\chi\) \%** \\ \hline PLA & 65.0 & - & - & 146.0/163.3 & 40.5 & 43.2 \\ PHB & - & - & - & 175.0 & \(-\)92.7 & 63.5 \\ PLA–chitosan & 62.8 & 113.7 & 6.1 & 155.0/161.5 & \(-\)29.2 & 24.6 \\ PHB–chitosan & - & - & - & 165.4/177.7 & \(-\)75.2 & 51.5 \\ PLA–chitosan Fe\({}^{3+}\) sorbed & 61.3 & 107.0 & 12.6 & 154.0/160.8 & \(-\)34.1 & 22.9 \\ PHB–chitosan Fe\({}^{3+}\) sorbed & - & - & - & 165.0/176.0 & \(-\)73.0 & 50.0 \\ \hline \end{tabular}
\end{table}