## 4 Conclusions  
The influence of three different metal oxide nanofillers on PLA thermal properties has been studied. Experimental results demonstrated a reduction in the \(t_{1/2}\) of PLA composites during non-isothermal cold crystallization, revealing the heterogenous nucleation efficiency of nanofillers. The Hoffman-Lauritzen theory, combined with the isoconversional approach of [PERSON], was applied on the DSC data to study the kinetics of non-isothermal cold crystallization. All nanocomposites show smaller \(E_{\alpha}\) and reduced nucleation activity factor \(\varphi\) compared to neat PLA, which means they enhanced 3D nucleation and are active as heterogeneous nucleating agents. According to PLM observations, the size of the spherulites of nanocomposites was found to be slightly smaller in comparison with neat PLA, which agrees with the faster crystallization rates of the nanocomposites during the non-isothermal cold crystallization. Additionally, the kinetic analysis was performed on PLA nanocomposites through thermogravimetry using the isoconversional and model \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Mechanism**} & **Activation** & **Pre-Exponential** & \multirow{2}{*}{**Reaction Order/n**} & **Log Kcat** & **Regression** \\  & & **Energy/(kJ/mol)** & & **Factor/s\({}^{-1}\)** & & **Coefficient** \\ \hline PLA & Cn & 159.7 & 11.49 & 0.98 & 0.80 & 0.9997 \\ \hline PLA ZnO & Cn & 84.5 & 4.86 & 0.64 & 1.17 & 0.9996 \\ \hline PLA Ag & Cn & 143.5 & 8.96 & 0.88 & 0.92 & 0.9998 \\ \hline PLA TiO\({}_{2}\) & Cn & 110.9 & 6.01 & 0.92 & 1.33 & 0.9998 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Activation energy, pre-exponential factor, and reaction order of neat PLA and PLA composites. Figure 9: Mass (%) curves and the corresponding fitting curves of (**a**) neat PLA, (**b**) PLA ZnO, (**c**) PLA Ag, and (**d**) PLA TiO\({}_{2}\) at various heating rates. fitting methods. 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. All methods show the same trend in the reduction of \(E\), which follows the order: PLA \(>\) PLA Ag \(>\) PLA TiO\({}_{2}>\) PLA ZnO. We can conclude that the TiO\({}_{2}\) and Ag nanoparticles cause a decrease in the \(E\) values of the PLA matrix without affecting the thermal stability and thermal degradation process in the polymer matrix. The following are available online at [[https://www.mdpi.com/article/10.3390/app11073004/s1](https://www.mdpi.com/article/10.3390/app11073004/s1)]([https://www.mdpi.com/article/10.3390/app11073004/s1](https://www.mdpi.com/article/10.3390/app11073004/s1)): Figure S1. DSC heating scans of PLA and its composites with heating rates (a) 2.5 \({}^{\circ}\)C/min, (b) 5 \({}^{\circ}\)C/min, (c) 7.5 \({}^{\circ}\)C/min, (d) 10 \({}^{\circ}\)C/min, (e) 15 \({}^{\circ}\)C/min, (f) 20 \({}^{\circ}\)C/min. Figure S2. Relative crystallinity (\(X_{\text{t}}\)) as a function of time during non-isothermal cold crystallization. Figure S3. Ozawa plots of the non-isothermal cold crystallization of PLA and its nanocomposites. Figure S4. Mo plots of the non-isothermal cold crystallization of PLA and its nanocomposites. Figure S5. Kissinger plots for the non-isothermal cold crystallization of PLA and its nanocomposites. Figure S6. Friedman plots of PLA and its nanocomposites. Table S1. Thermal characteristics of PLA and its composites obtained from the DSC scans of Figure S1. Table S2. Results of the Mo analysis of the non-isothermal cold crystallization of PLA and its nanocomposites. Conceptualization, D.N.B., Z.T., K.C., and L.F.Z. ; methodology, Z.T. and E.T. ; software, Z.T. and E.T. ; validation, Z.T. and E.T. ; formal analysis, Z.T., G.Z.P., and E.T. ; investigation, K.P.C., Z.T., A.Z. and E.T. ; resources, D.N.B. and L.F.Z. ; writing--original draft preparation, Z.T., K.P.C., and E.T.