## 3 Results and Discussion  
### Semi-Crystalline Structure of Materials  
The crystallization behavior was determined from a heat-cool-heat cycle using DSC for neat, nanocomposite and aged materials. The crystallization temperature (T\({}_{\rm c}\)), melting temperature (T\({}_{\rm m}\)) and the degree of crystallinity (X\({}_{\rm C}\)) are gathered in Table 1.  
The results indicate that the aging significantly affected the thermal properties of the materials with roughly similar effects on both polyesters. In the case of PBSA materials, the T\({}_{\rm m}\) values did not appear significantly modified after accelerated aging. In contrast, the crystalline transition was significantly impacted with a decrease and the X\({}_{\rm C}\) increasing significantly. Concerning the PHBV materials, the T\({}_{\rm m}\) and T\({}_{\rm c}\) decreased significantly after aging. The X\({}_{\rm C}\) tended to increase but to a lesser extent compared to PBSA materials. The effect of irradiation on PBSA [21; 22] and PHBV [23; 24; 25] has already been studied and similar results were obtained. The decrease of the T\({}_{\rm c}\), observed with both materials, was attributed to chain scission mechanism leading to the formation of shorter polymer chains. This reduction in chain size should result in an increase in mobility (and therefore freedom of movement) that allows structural rearrangement of polymers in a crystalline state at a lower temperature compared to long polymer chains [23; 26]. Regarding the T\({}_{\rm m}\), for PHBV, a decrease was observed and double melting peaks appeared, which indicate changes in the crystal structures of polymers. The decrease of T\({}_{\rm m}\) may also be attributed to the decrease in molar mass of polymer chains, this hypothesis being supported in several studies by the determination of the number average molecular weight (\(\overline{\rm M}_{\rm n}\)) by size-exclusion chromatography (SEC) [27; 28; 29; 25]. The increase of the degree of crystallinity observed was as initiated by the scission of polymer chains, due to irradiation, particularly in amorphous regions, which are more accessible for degradation. The higher mobility of these shorter chains allows them to recrystallize easily. This phenomenon was more marked in the case of PBSA, whose degree of crystallinity was initially lower, and consequently, amorphous regions were more important.  
Finally, it is important to point out that the increase of the degree of crystallinity was visually confirmed since the materials became very brittle compared to unaged control materials (Figure 1). The addition of nanoclays does not seem to have any effect on the impact of accelerated aging, either on crystallization and melting temperatures or on the degree of crystallinity. From a mechanical point of view, they seem to play a reinforcing role by slightly preserving the ductility of the materials, this effect being more noticeable on the PBSA.  
\begin{table}
\begin{tabular}{l l l l l} \hline  & & **T\({}_{\rm c}\) (\({}^{\circ}\)C)** & **T\({}_{\rm m}\) (\({}^{\circ}\)C)** & **X\({}_{\rm C}\) (\%)** \\ \hline \multirow{2}{*}{PBSA} & Control & 42.3 \(\pm\) 0.1 & 86.7 \(\pm\) 0.4 & 45.6 \(\pm\) 0.6 \\  & UV treated & 39.8 \(\pm\) 3.7 & 88.4 \(\pm\) 1.8 & 53.7 \(\pm\) 1.9 \\ \hline \multirow{2}{*}{PBSA NCP} & Control & 44.0 \(\pm\) 0.3 & 87.2 \(\pm\) 0.6 & 45.8 \(\pm\) 0.5 \\  & UV treated & 33.4 \(\pm\) 0.1 & 86.6 \(\pm\) 1.4 & 53.4 \(\pm\) 2.3 \\ \hline \multirow{2}{*}{PHBV} & Control & 122.1 \(\pm\) 0.1 & 169.1 \(\pm\) 0.7 & 54.1 \(\pm\) 1.2 \\  & UV treated & 117.8 \(\pm\) 0.1 & 166.1 \(\pm\) 0.4 & 55.5 \(\pm\) 0.8 \\ \hline \multirow{2}{*}{PHBV NCP} & Control & 122.3 \(\pm\) 0.1 & 171.5 \(\pm\) 0.9 & 52.7 \(\pm\) 0.9 \\  & UV treated & 119.9 \(\pm\) 0.4 & 168.2 \(\pm\) 1.8 & 53.5 \(\pm\) 0.7 \\ \hline \end{tabular}
\end{table}
Table 1: Crystallization temperature (T\({}_{\rm c}\)), melting temperatures (T\({}_{\rm m}\)) and crystallinity degree (X\({}_{\rm C}\)) of neat and nanocomposite PBSA and PHBV and the corresponding aged materials.