## 3 Results
### Thermometric Characterization  
DSC is a common method used to analyze the effects of tanning and retanning components on the collagen matrix by calculating the energy consumption (\(\Delta\)H). Increasing the denaturation temperature and enthalpy indicates better cross-linking action through the collagen fiber network [35]. Variation in denaturation enthalpy areas indicates differences in material structure which are directly related to the reagent used during the leather manufacturing process [36]. The DSC curves of the specimens are given in Figure 3; chromium-tanned bovine leather gained the highest denaturation temperature and enthalpy areas of \(106.83\,^{\circ}\)C and \(-813.27\,\mathrm{g}^{-1}\), respectively. Additionally, the leathers retanned with alginate (except sample #9) show better thermal performance than vegetable-tanned bovine and chromium-tanned ovine leathers, which indicates the compatible synergy of alginate with wet-white tanning reagent. Alginate, a polysaccharide derived from seaweed, may introduce different functional groups and bonding capabilities compared to the polyphenic compounds typically found in vegetable tannins. These additional functional groups can participate in stronger or more numerous intermolecular interactions with collagen, resulting in greater thermal stability and higher enthalpy. Additionally, the linear structure of alginate allows for more uniform and consistent interactions with collagen fibers. In contrast, the complex and variable nature of vegetable tannins can lead to less effective binding and cross-linking, resulting in lower thermal performance and enthalpy values. The higher thermal decomposition values among the alginate-based retanned leathers belong to samples #7 (\(98.78\,\mathrm{\SIUnitSymbolCelsius}\), \(-585.77\,\mathrm{J}\,\mathrm{g}^{-1}\)), #10 (\(87.08\,\mathrm{\SIUnitSymbolCelsius}\), \(-323.47\,\mathrm{J}\,\mathrm{g}^{-1}\)), #8 (\(87.07\,\mathrm{\SIUnitSymbolCelsius}\), \(-334.04\,\mathrm{J}\,\mathrm{g}^{-1}\)), and #9 (\(78.5\,\mathrm{\SIUnitSymbolCelsius}\), \(-183.19\,\mathrm{J}\,\mathrm{g}^{-1}\)). The results showed that the use of Tara with alginate solution did not affect the thermal performance of the leathers positively, as was expected. Since the denaturation temperature of sheep collagen is lower than that of bovine [37; 38], the DSC performances of chromium-tanned ovine (#1) leather were determined to be \(87.3\,\mathrm{\SIUnitSymbolCelsius}\) and \(-214.90\,\mathrm{J}\,\mathrm{g}^{-1}\). Due to the difference in characteristic structure of collagen-based leathers and leather alternatives (#4, #5, and #6), the thermal behavior of the specimens was interpreted separately. In the DSC thermograms, there were two exothermic peaks belonging to sample #5 and sample #6. The DSC curves of sample #5 (first peak: \(43.94\,\mathrm{\SIUnitSymbolCelsius}\), \(-16.15\,\mathrm{J}\,\mathrm{g}^{-1}\); second peak: \(165.55\,\mathrm{\SIUnitSymbolCelsius}\), \(29.91\,\mathrm{J}\,\mathrm{g}^{-1}\)), and sample #6 (first peak: \(58.24\,\mathrm{\SIUnitSymbolCelsius}\), \(-43.70\,\mathrm{J}\,\mathrm{g}^{-1}\); second peak: \(265.13\,\mathrm{\SIUnitSymbolCelsius}\), \(-6.77\,\mathrm{J}\,\mathrm{g}^{-1}\)) were found to be similar to those of the composite containing polylactic acid (PLA) [39; 40]. It is known that PLA containing hydroxyl and carboxyl groups is popular in crystalline biomaterials used in the production of biodegradable and biocompatible substances for packaging and drug applications. The DSC thermogram of sample #4 showed that there were two main peaks at \(186\,\mathrm{\SIUnitSymbolCelsius}\) (\(\Delta\mathrm{H}=605.80\,\mathrm{J}\,\mathrm{g}^{-1}\)) and \(367\,\mathrm{\SIUnitSymbolCelsius}\) (\(\Delta\mathrm{H}=88.14\,\mathrm{J}\,\mathrm{g}^{-1}\)) belonging to PVC and PU. It is known that PU, with its high toughness, is modified by PVC to obtain more flexible materials [41].