## 3 Results and Discussion
### Structural and Morphological Consequences of Processing  
#### 3.1.1. _Molar Mass_  
The molar mass of polymers is a critical factor in determining other physico-chemical properties, such as thermal, chemical, or mechanical stability [77]. Hence, the consequences of the successive processing stages and the contribution of both PEG and NFC on the molar mass of PLA were first ascertained. Figure 2 plots the obtained Gaussian-like molar mass distributions, which were displaced towards lower values after processing due to mechanical and thermal degradation. The contribution of PEG and NFC after each processing stage was studied in detail with the aid of the average molar mass in number (\(M_{n}\)) and weight (\(M_{w}\)), plotted in Figure 3 and gathered in Table S1. After compounding, both the average molar mass in the number (\(M_{n}\)) and weight (\(M_{w}\)) of PLA were reduced due to high temperatures and shear stresses in the torque rheometer [26]. This decrease was more significant in the \(M_{w}\) than in the \(M_{n}\) due to the breakage of long PLA chains. The use of low molar mass PEG in PLA-400 resulted in more chain scission in the PLA matrix, together with the possibility of establishing crosslinks with broken PLA chains. Nevertheless, in the PLA-1500, the higher molar mass of PEG slightly buffered the consequences of compounding in terms of molar mass reduction. As for the molar mass distributions, the chain breakage when PEG was incorporated was demonstrated by the low molar mass population with a peak around \(\sim\)3 \(\times\) 104 g/mol. Regarding the role of NFC, it has been reported that it can cause shear effects during compounding and promote more degradation [78; 79; 80]; its contribution was non-critical and not perceivable in either the molar mass distributions or the calculated results. Only a minor additional decrease in the molar mass could be detected (\(<\)10%), especially in the \(M_{n}\) of PLA-400-NF nanocomposites. The subsequent injection molding to obtain dog-bone specimens significantly affected the molar mass. Indeed, distributions moved towards lower values, and a more relevant low-molar mass cue was appreciated, which determined the variation of \(M_{n}\). A different pattern was found for pure PLA than for blends and nanocomposites. For PLA, \(M_{n}\) and \(M_{w}\) were slightly reduced (14% and 8%), while the molar mass reduction in the plasticized PLA and PLA-PEG-NFC nanocomposites after injection molding was significantly higher (\(>\)40% and \(>\)24%, respectively). At this point, non-relevant differences according to the molar mass of the PEG could be identified in the molar mass distributions However, a 10-15% reduction was found in the \(M_{n}\) of PLA-400-NFC bionanocomposites caused by NFC. Nevertheless, the influence of the NFC was non-critical and a general tendency correlated to the NFC percentage in the nanocomposites could not be established. Finally, the compression molding stage to obtain films correspondingly reduced the molar mass in all of the compositions, but more restrainedly. \(M_{n}\) and \(M_{w}\) were further reduced for PLA (19% and 28%), while for the plasticized PLA-400 and PLA-1500 and bionanocomposites, the molar mass reduction was especially relevant in the \(M_{w}\) (>31%). Apart from the displacement towards lower values, their molar mass distributions also showed a sharp peak at -10\({}^{4}\) g/mol. This peak is ascribed to the generation of a polymer chain population with lower molar mass due to chain scission caused by the intensive temperature and pressure applied during thermo-compression regardless of the molar mass of PEG. Once more, the contribution of NFC did not significantly affect the molar mass distributions, with variations in the \(M_{n}\) and \(M_{w}\) values lower than 10% in comparison to their PLA-PEG counterparts. Nevertheless, as the NFC content increased, a greater molar mass was identified in the PLA-1500-NFC compositions.