## 3 Results and Discussion
### Thermal Degradation Study of PLA Composites
These complications are quite important, particularly in the case where competitive mechanisms are involved in the entire reaction. Figure 8 shows the calculated \(E\) values versus the degree of conversion \(\alpha\) for neat PLA and PLA composites filled with metal oxide nanofillers. The mean \(E\) values of neat PLA and PLA TiO\({}_{2}\), PLA Ag, and PLA ZnO composites, calculated by the Friedman method, were found to be 156, 136, 105, and 84 kJ/mol, respectively, while the \(E\) values were 155, 142, 110, and 84 kJ/mol using the OFW method. The \(E\) values for neat PLA and its nanocomposites remain almost constant over the entire conversion range, indicating that one process takes place during the thermal degradation of the samples. Such consideration is plausibly reasonable because similar implications can also be drawn from TGA and 1 st dTG results. All PLA nanocomposites have lower \(E\) values than neat PLA, followed by the nano-Ag, TiO\({}_{2}\), and the nano ZnO, requiring less activation energy to undergo thermal degradation. The trend observed for calculated values is consistent with the trend of non-isothermal cold crystallization analysis, and such catalytic effect follows the order ZnO \(>\) TiO\({}_{2}\) \(>\) Ag, in agreement with literature results [26]. The multivariate non-linear regression method, or model-fitting method, was used to determine the kinetic triplet and the degradation mechanism of PLA composites filled with metal oxide nanofillers [79, 81]. The efficiency of each reaction model is estimated by the correlation quality between the experimental and the theoretical results. In this study, the thermal decomposition of the neat PLA and PLA composites filled with metal oxide nanofillers can be best described by the \(Cn\) autocatalysis n-order mechanism (\(f(\alpha)=\left(1-\alpha\right)^{n}(1+K_{cat}X)\)), Figure 9. The addition of the fillers into the PLA matrix has led to no change in the decomposition process, but the catalytic effect turns to prevail over the stabilizing effect, especially in the case of the ZnO filler. Table 3 presents the calculated \(E\) values, pre-exponential factor, and the reaction order for neat PLA and PLA composites with metal oxide nanofillers. It should be noted that that the \(E\) values were found to be similar to those determined by the OFW analysis and [PERSON]'s method (Figure 8). The calculated \(E\) value of neat PLA was found to be 159.7 kJ/mol, in agreement with the literature [82, 83]. Moreover, the calculated \(E\) values of PLA composites suggest that the metal oxide nanofillers, added to the polymer matrix, have led to greatly decreased \(E\) and resulted in a substantially higher decomposition rate  
constant. Once again, all methods show the same trend in the reduction of \(E\), which follows the order: PLA > PLA Ag > PLA TiO\({}_{2}\) > PLA ZnO. The pre-exponential factor of the PLA composites presents lower values than neat PLA, in accordance with the calculated E values. This means that the rate constant of PLA composites is significantly larger than that of neat PLA, accelerating the thermal degradation. However, it should be noted that the TiO\({}_{2}\) and Ag nanoparticles cause a decrease in the \(E\) values of the PLA matrix without affecting the thermal degradation process and thermal stability. Figure 8: Calculated activation energy (E) for the thermal degradation of neat PLA and its nanocomposites by using (**a**) the [PERSON] method, and (**b**) the Ozawa, Flynn, and Wall analysis.