*3.3. Thermal Behavior Assessment*

DSC studies were performed to investigate the effect of PEG addition on the PLA/starch composite. In addition, changes in the thermal properties of composites after using ethanol

as the PEG solvent instead of acetone were observed. Figure 3 presents DSC analysis of PSES, PSE2, PSE3, PSE<sup>22</sup> and PSE32. In the case of PSE2, PSE3, PSE<sup>22</sup> and PSE<sup>32</sup> samples, there are three peaks visible—50–70, 100–120 and 140–160 ◦C. The first one (50–70 ◦C) pertained to the glass transition temperature (Tg) followed by changes in the PEG phase. The second one (100–120 ◦C) is related to the crystallization temperature (Tc) of PLA and the third one (140–160 ◦C) was attributed to the melting temperature (Tm). As there is no significant change in the T<sup>g</sup> and T<sup>m</sup> in all samples, it can be concluded that the addition of PEG did not considerably affect the mobility of the polymeric chains [62]. A former study had shown that starch content in the PLA/starch blend had little effect on the T<sup>m</sup> [63]. However, after the incorporation of PEG, T<sup>g</sup> decreased slightly, which can be attributed to PEG's emulsifier properties as well as its role as binding molecules between the hydrophobic (PLA) and the hydrophilic (starch) phases [64,65]. In the DSC curve of the PSE<sup>s</sup> sample, two peaks are observable, referring to the T<sup>g</sup> and T<sup>m</sup> and the reason why no endothermic peak was seen pertained to using no emulsifier in this sample. The obtained results showed that PLA and starch were combined well through the solvent evaporation technique. The area under the T<sup>g</sup> and T<sup>m</sup> peaks gives information about the crystallinity percentage of samples. Therefore, it can be concluded that the addition of the emulsifier caused a decrease in the sample's crystallinity, making the modified samples susceptible to a faster degradation [66]. With the addition of PEG to PLA/starch, the T<sup>c</sup> peak appeared in the DSC diagram of PSE2. Then, the T<sup>c</sup> of PSE<sup>3</sup> increased with an increment in the content of PEG compared to PSE2, indicating an increase in the Tc. These results are in accordance with SEM findings which showed that PEG-containing samples have faster degradation rates. After using ethanol instead of acetone as PEG solvent (PSE<sup>22</sup> and PSE32), the peak at T<sup>m</sup> was separated and reduced. This reduction in T<sup>m</sup> intensity indicates a decrease in the crystallinity of the samples using ethanol solvent. It was also proved before that the amorphous structures show faster degradation rates [67]. This is again in accordance with SEM and mechanical properties results that ethanol-based samples showed higher degradation rates. On the other hand, the T<sup>c</sup> was increased and the corresponding peak was broadened. These observations could be due to the uniformity of the composites and the better distribution of PEG after the application of ethanol as the solvent, which has increased the emulsifying effect of PEG on PLA/starch.
