## 3 Results and Discussion
### Structural and Morphological Consequences of Processing
#### 3.1.2 Thermal Properties and Crystalline Structure
These low percentages of NFC may have assured a good dispersion that increased tortuosity for the mobility of the PLA macromolecules and moved the glass transition toward higher temperatures. As the NFC content increased, the slightly lower effect on the glass transition may suggest the possible agglomeration of the filler, with a minor hinderance to the translational and rotational backbone motions of the PLA chains [85]. The NFC also favored cold crystallization at lower temperatures and influenced the melting event that resulted in a higher crystalline degree. This performance, more relevant for the PLA-400 than the PLA-1500-based compositions, may be ascribed to the nucleating behavior of the nanoparticles [86]. The comprehensive analysis of the degree of crystallinity revealed that, in both PLA-400-NFC and PLA-1500-NFC nanocomposites, a limit concentration for the nucleating function in the range from 1 to 3 wt% of nanoparticles was found. As mentioned before, the agglomeration of NFC at higher percentages may have caused a lower nucleating effect and, therefore, a slightly lower degree of crystallinity. This behavior was in line with different studies in the literature, all referring to a nucleating effect of the nanofillers up to agglomeration [25; 86; 87; 26]. Finally, in terms of lamellar thickness, the contribution of the NFC could be appreciated, especially in the PLA-400-NFC nanocomposites, with a slight reduction of \(l_{c}\) from 13.1 to 12.7 nm due to less crystalline perfection. In the PLA-1500-NFC nanocomposites, the \(l_{c}\) remained around 13.2 nm. After the injection and compressioning stages, the obtained thermograms and selected key indicators (\(T_{g}\), \(X_{c}\), and \(l_{c}\)) were altered in all of the assessed materials with relevant differences as a function of the composition. Pure PLA showed the cold-crystallization transition in the vicinities of 112 \({}^{\circ}\)C after injection molding and gained importance and moved to 110 \({}^{\circ}\)C after thermo-compression. This performance is strictly related to chain scission during processing and is a sign of degradation. Shorter polymer chains have greater mobility and more ability to rearrange during cold-crystallization. Subsequently, a more relevant melting event was observed in the PLA during heating. Altogether, the crystallinity and lamellar thickness increased from 2% to 12% and 13.3 nm to 14.1 nm, respectively. Particularly after compression molding, the melting transition turned from a unimodal to a bimodal pattern, which may be correlated to distinct crystalline populations, with the lower being less prominent with an \(l_{c}\) of 12.1 nm. This performance, previously reported for reprocessed PLA [34], was accompanied by an increase in the glass transition along the different processing stages from 56 \({}^{\circ}\)C to 58 \({}^{\circ}\)C. The generation of more crystalline regions with higher lamellar thickness promoted steric hindrance in the amorphous regions, resulting in higher glass transition temperatures. The inclusion of PEG decreased the glass transition temperature after injection and compression molding. The reduction of the molar mass of PLA that generated oligomers, along with the presence of PEG as a plasticizer, allowed for higher mobility, and therefore the glass transition was displaced towards even lower temperatures from \(\sim\)42 \({}^{\circ}\)C to \(\sim\)40 \({}^{\circ}\)C in both blends. While the cold-crystallization disappeared after dog-bone and film processing, the melting event remained a well-defined transition in all cases, given that the PLA managed to reach its potential crystallinity. Consequently, the degree of crystallinity significantly increased after reprocessing the PLA-400 from 26% to 39% and less prominently for the PLA-1500 from 25% to 32%. The lamellar thickness decreased in the PLA-400 from 13.1 nm to 12.8, remaining around 13 nm for the PLA-1500 after the subsequent processing stages.