# Effect of LNR-g-MMA on the Mechanical Properties and Lifetime Estimation of PLA/PP Blends
## 3 Results and Discussion
### Thermal Analysis  
#### 3.4.1 Thermal Stability  
According to ASTM E 1877 [39], which provides the necessary mathematical processes employed in determining activation energy and lifetime, TGA analyses were carried out, followed by the evaluation of the thermal stability, kinetics of degradation, and lifetime of the PLA, PP, and PLA/PP blends. All polymers were heated at rates of 10, 20, 30, and 40 \({}^{\circ}\)C/min, between 50 and 800 \({}^{\circ}\)C in an atmosphere of air. The TG and DTG curves for the neat polymers and polymer blends of PLA/PP ratios 70:30 wt%, and LNR\(-\)g\(-\)MMA with a content of 0.0, 2.5, 5.0, and 10.0 phr as a compatibilizer used in the current study, are shown in Figures 6 and 7 for the four used heating rates. Both neat polymers showed single\(-\)stage decomposition as shown in Figure 6a,b. Unlike the neat PP and PLA, the two\(-\)step degradation process in immiscible polymer blends was clearly seen in PP/PLA blends, as shown in Figure 6c-f. The DTG curves (Figure 7c-f) identified two decomposition peaks. More notably, the first peak was related to the decomposition of the blend's PLA, while the second peak, which appeared at a higher temperature, is associated with the degradation of PP [40]. The decomposition temperature shifted toward a higher temperature with the increase in heating rate. The TG data showing the thermal degradation temperatures of the neat polymers and polymer blends of PLA/PP ratios 70:30 wt%, using an LNR\(-\)g\(-\)MMA content of 0.0, 2.5, 5.0, and 10.0 phr as a compatibilizer, are listed in Table 1. The initial temperature (T\({}_{i}\)) and the final temperature (T\({}_{f}\)) were obtained with a bitangent method, and T\({}_{m}\) is the temperature at the maximum weight loss rate, which can be obtained from the peak of the DTG at different heating rates (Figure 7). All blends under investigation showed an exothermic effect consistent with the thermal degradation process. Compared to the neat PP, the thermal decomposition curve of neat PLA shifted towards low temperatures, indicating that PLA was less thermally stable than PP. The incorporation of PP significantly changed the degradation temperature trends. Blending PLA with PP (70:30 wt%) increased the blend's thermal stability or made it more resistant to temperature compared to the pure PLA, but the addition of a compatibilizer decreased the blend's thermal stability by increasing interfacial adhesion and interaction between polymer phases.  
Figure 6: Thermogravimetric analysis (TG) curves of (a) PLA, (b) PP, and PLA/PP blends with LNR\(-\)g\(-\)MMA of (**c**) 0.0, (**d**) 2.5, (**e**) 5.0, and (**f**) 10.0 phr.  
to 144.9 kJ/mol. In comparison, the E\({}_{\text{a}}\) values (w = 0.05) of PLA/PP/LNR\(-\)g\(-\)MMA (70:30:2.5 phr), PLA/PP/LNR\(-\)g\(-\)MMA (70:30:5.0 phr), and PLA/PP/LNR\(-\)g\(-\)MMA (70:30:10.0 phr) were 134.3, 125.5, and 109.8 kJ/mol, respectively. The addition of PP in PLA increased the activation energy due to the incompatibility between the two polymers. Comparatively, adding a compatibilizer improved the compatibility of the two polymers and lowered the activation energy, decreasing the blends' thermal stability.