## 3 Results and Discussion
### Structural and Morphological Consequences of Processing
#### 3.1.3 Thermo-Oxidative Stability  
The thermo-oxidative stability of the materials after the different processing stages was also analyzed, as it may bring a complementary view to the study of the molar mass and crystalline morphology. The obtained thermogravimetric thermograms (TG) and derived curves (DTG) are displayed in Figures S4 and S5 of the Supplementary Materials, respectively. These thermograms were assessed in detail in terms of the onset temperature (\(T_{o}\)) and primary decomposition process (\(T_{p}\)) of PLA, which were considered critical parameters for evaluating the consequences of reprocessing, and are reported in Table 2.  
Pure PLA revealed a single-stage decomposition process with an onset of around 332 \({}^{\circ}\)C. Beyond this point, the weight loss increased, and the decomposition reached its maximum rate at 356 \({}^{\circ}\)C and finished at about 370 \({}^{\circ}\)C. According to the literature, the starting point for the decomposition of virgin PLA can be related to the loss of end groups from the main chain or ester bond scission [88; 89], which ultimately results in the decomposition of the polymer backbone [68]. Finally, a minor step from 400 to 500 \({}^{\circ}\)C is due to the subsequent char decomposition [90; 91]. Once compounded, the thermo-oxidative decomposition of plasticized PLA-400 and PLA-1500 showed a two-stage profile. The first stage, with a peak temperature of 245 \({}^{\circ}\)C and a weight loss of \(\sim\)7%, may be attributed to the decomposition of PEG, in which the mass percentage virtually matches its expected ratio in the blend [90]. Then, the second and main stage, between 330 \({}^{\circ}\)C and 375 \({}^{\circ}\)C, involved the principal mass loss due to the decomposition of the PLA backbone. Although the decomposition of PEG was observed in the blends at lower temperatures, it did not alter the onset and peak temperatures of the main decomposition stage of PLA (\(T_{o}\) and \(T_{p}\)). In the compounded nanocomposites, the NFC promoted a general slight displacement of the curve towards higher temperatures, especially for lower percentages of NFC (1 and 3 wt%) in the PLA-400-based materials. All the curves were displaced towards higher temperatures with the addition of low portions of NFC, suggesting higher thermo-oxidative stability. As perceived in previous sections, a key point discussing the stability of the compositions with high NFC percentages may be the nanoparticles' level of dispersion. The agglomeration of the nanofibrillated cellulose in concentrations above 3 wt% may prevent a proper distribution of the filler into the matrix, which impairs improving the thermo-oxidative stability of the bionanocomposites [28]. Nevertheless, as reported by other authors with similar amounts of NFC, only a limited effect of such nanoparticles was found on the thermal stability of PLA nanocomposites [27]. After the subsequent injection and compression molding, the decomposition of PEG in the blends appeared at lower temperatures. However, the presence of NFC in the bionanocomposites buffer this diminution, and even greater temperatures for this first mass loss process ascribed to PEG could be identified. This effect was more relevant in the PLA-400-NFC compositions and can be attributed to the interaction of PEG with the NFC nanoparticles, which was more significant the lower the molar mass of PEG. The successive processing stages moved the onset of decomposition towards lower values. The degraded PLA chains with more presumable carboxylic chain ends may have promoted an earlier onset of decomposition. This behavior could be observed in both the plasticized PLA-400 and PLA-1500 compositions. However, in the bionanocomposites, a noticeable difference was perceived. On the one hand, in PLA-400-NFC, the presence of NFC accentuated the reduction of the \(T_{o}\). However, in the PLA-1500-NFC nanocomposites, the higher molar mass of PEG seemed to contribute to reducing this fall.