## 3 Results and Discussion
### Structural and Morphological Consequences of Processing
#### 3.1.2 Thermal Properties and Crystalline Structure  
The change in molar mass is widely known to promote variations in the crystalline structure of PLA and, consequently, in the thermal properties. Therefore, calorimetric analyses were carried out during subsequent heating-cooling-heating scans. While the  
Figure 3: Average molar mass in number (\(M_{n}\)) (up) and weight (\(M_{w}\)) (down) for the PLA-400 (left) and PLA-1500-based bionanocomposites (right) after the subsequent stages of compounding, dog-bone, and film processing stages. A standard deviation below 5% was omitted for the sake of clarity. first heating scan erases the thermal history of the samples and removes the existing crystalline state given by the processing conditions, the controlled cooling scan at a given rate guarantees the creation of a known and identical thermal history for all of the assessed samples. Thus, materials can be intrinsically evaluated in the second heating scan, avoiding the specific effects of processing, storage, or transportation. The thermograms of the first heating and subsequent cooling scans are illustrated in Figures S2 and S3 of the Supplementary Materials. Those of the second heating segment are shown in Figure 4. The glass transition temperature (\(T_{g}\)) measured in the cooling scan, together with the degree of crystallinity (\(X_{c}\)) and the lamellar thickness (\(l_{c}\)) calculated in the second heating scan, were selected as key indicators of the crystalline structure and are plotted in Figure 5 and gathered in Table S1. Figure 4: Calorimetric thermograms for the second heating scan of PLA, plasticized PLA-PEG, and PLA-PEG-NFC bion nanocomposites after the subsequent stages of compounding, dog-bone, and film specimen preparation. Pure PLA pellets showed a glass transition at 56 \({}^{\circ}\)C, followed by a small melting peak that resulted in a predominant amorphous structure with a degree of crystallinity of 2% and a lamellar thickness of 13.3 nm. These values are in line with those previously reported for this PLA grade [26,28]. The glass transition temperature of compounded plasticized PLA decreased by 25%, given the plasticizing effect of PEG and chain scission caused by compounding. The \(T_{g}\) of PLA-400 was 42 \({}^{\circ}\)C, while that of PLA-1500 was 43 \({}^{\circ}\)C. In addition, the thermogram of PLA-PEG blends shows a vanishing of structural relaxation, in line with other studies dealing with plasticized PLA [81, 82, 83]. The molecules of PEG may have acted as enhancers  
Figure 5: Glass transition temperature (\(T_{g}\)), degree of crystallinity (\(X_{c}\)), and lamellar thickness (\(l_{c}\)) for the bion nanocomposites after the subsequent stages of compounding, dog-bone, and film specimen preparation. A standard deviation between 1% and 5% was omitted for the sake of clarity. of molecular packing, establishing hydrogen bonding, dipole-dipole physical interactions, or even chemical crosslinks with PLA macromolecules during compounding. As a result, some rigid homogeneous PLA-PLA interphases were replaced by heterogeneous flexible PLA-PEG networks, decreasing the enthalpy and avoiding the perception of structural relaxation. This hypothesis was thoroughly demonstrated in other plasticized polymers [84]. Moreover, the PEG promoted the cold crystallization process at temperatures below 80 \({}^{\circ}\)C, given the higher mobility of PLA chains that can rearrange during heating. Finally, an intense melting peak was detected for both plasticized PLAs. The degree of crystallinity increased in the plasticized PLA up to 27% for PLA-400 and 25% for PLA-1500, and the lamellar thickness slightly decreased to 13.1 nm regardless of the molar mass of the PEG. Therefore, more crystals with thinner lamellae were produced in the plasticized PLA [45; 46]. The addition of NFC slightly increased the glass transition temperature after compounding compared to their PLA/PEG counterparts, especially for low NFC percentages (1 to 3 wt%).