## 3 Results
### Detailed Analysis of FTIR Crystallinity Estimator at Different Polarisation Angles
The \(R\)-value significantly decreases for antiparallel crystalline domains but increases for parallel vibration orientations. Both regions are undergoing decomposition. Additionally, the antiparallel arrangements seem to undergo structural changes, as only degradation products corresponding to parallel arrangements are present in historical samples and samples aged under harsh conditions (esO\({}_{2}\)/VOC/H\({}_{2}\)O). The changes in \(R\)-values coincide with the order parameter \(S\)-values approaching zero during aging, indicating a decrease in ordering in both parallel and antiparallel crystalline pleats. Similarly to \(R\)-values, the \(S\) parameter drops below zero for samples aged under the harshest conditions (esO\({}_{2}\)/VOC/H\({}_{2}\)O) and for naturally aged historical samples. This suggests a transition to more parallel moments of transition geometry with vibrations becoming more perpendicular to the molecule's axis but different from parallel  
Figure 6: Dichroic ratio \(R\) and order parameter \(S\) calculated from pol-ATR-FTIR for two bands in the superimposed Amide I region of the spectra (bands centered at 1620 and 1699 cm\({}^{-1}\)). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample’s Name** & **MS** & \multicolumn{3}{c}{**isO\({}_{2}\)**} & \multicolumn{3}{c}{**esO\({}_{2}\)**} & \multicolumn{3}{c}{**esO\({}_{2}\)/VOC/H\({}_{2}\)O**} \\ \hline  & **1620** & **1699** & **1620** & **1699** & **1620** & **1699** & **1620** & **1699** \\ \(R\) & 0.368 & 3.005 & 0.438 & 1.572 & 0.486 & 1.776 & 0.751 & 0.675 \\ (+/\(-\)) & 0.027 & 0.095 & 0.013 & 0.012 & 0.023 & 0.109 & 0.014 & 0.001 \\ \(S\) & \(-\)0.270 & 0.393 & \(-\)0.232 & 0.160 & \(-\)0.205 & 0.212 & \(-\)0.091 & \(-\)0.122 \\ \hline
**Sample’s name** & \multicolumn{3}{c}{**MS**} & \multicolumn{3}{c}{**IB**} & \multicolumn{3}{c}{**CB**} & \multicolumn{3}{c}{**FB**} \\ \hline  & **1620** & **1699** & **1620** & **1699** & **1620** & **1699** & **1620** & **1699** \\ \(R\) & 0.368 & 3.005 & 0.493 & 0.792 & 0.517 & 0.865 & 0.692 & 0.898 \\ (+/\(-\)) & 0.027 & 0.095 & 0.007 & 0.033 & 0.005 & 0.020 & 0.014 & 0.019 \\ \(S\) & \(-\)0.270 & 0.393 & \(-\)0.203 & \(-\)0.074 & \(-\)0.192 & \(-\)0.047 & \(-\)0.115 & \(-\)0.035 \\ \hline \hline \end{tabular} \(\Delta\) dichroic ratio R and \(\circ\) order parameter S calculated from pol-ATR-FTIR spectra  
\end{table} 
Table 3: Dichroic ratio \(R\) and order parameter \(S\) calculated from pol-ATR-FTIR for two bands in the superimposed Amide I region of the spectra (bands centered at 1620 and 1699 cm\({}^{-1}\)). pleats. In the antiparallel domains, two adjacent amide groups in the same chain are in-phase, while they are out-of-phase in the adjoining chain, similar to the parallel crystalline domain arrangement. This change could be attributed to the transformation of amino acids from L-amino acids to D-amino acids over time, as recommended by [PERSON] et al., for the Smithsonian Museum as a silk age calculator [41]. The flip between enantiomers in the crystalline regions may explain the observed changes in \(S\) and \(R\)-values, which are likely to decompose in this manner due to the overall behavior of D-peptides. [PERSON] his even proposes that introducing D-enantiomers into the crystalline structure can lead to the disappearance of the pleated structure in favor of rippled one instead of similar structures in nylons [42]. As demonstrated above, the polarizer provides a more comprehensive description of fibroin's secondary structure through FTIR spectra. Since it affects the IR absorption coefficient, it also influences the estimators calculated from the spectra. Figure 7 illustrates that the non-normalized crystalline estimator \(\mathrm{E_{C}}\) value changes significantly depending on the polarization angle. The highest value of the estimator is recorded at 0\({}^{\circ}\), while the smallest is at 90\({}^{\circ}\).