# Structural, Thermal and Mechanical Assessment of Green Compounds with Natural Rubber
## 3 Results
### Thermogravimetric Analysis  
Thermogravimetric analysis of natural rubber blended with different amounts of GTR from cars and trucks was conducted in a nitrogen atmosphere. These conditions allow only thermal degradation, avoiding the combined effect of thermal- and thermo-oxidative degradation in the presence of oxygen.  
The obtained results are presented in Figures 11 and 12 and summarized in Table 1. The data indicate an increase in thermal stability with the addition of GTR, regardless of the type of GTR used (car or truck), which is related to the better thermal stability of GTR in comparison to natural rubber. Likewise, the maximum decomposition temperature, estimated from derivative thermogravimetry (DTG), increases as a function of the amount of GTR, where the reference sample 100 NR has a peak at 398.5 \({}^{\circ}\)C, sample 100 NR50 GTRcar has a peak at 402.9 \({}^{\circ}\)C and sample 100 NR50 GTRtruck has a peak at 402.1 \({}^{\circ}\)C, respectively. This phenomenon is also related to the difference of compositions of GTR from cars and trucks. According to reference [30] GTRcar has an average composition of 14% of NR and 27% of SynR (synthetic rubber), while GTRtruck contains 27% of NR and 14% of SynR. The presence of synthetic rubber in particles of GTR increases the thermal stability, because the decomposition temperature is higher for SBR (main component of SynR) than in NR.  
Figure 11: TGA and DTG curves of 100 NR, 100 NR10 GTRc, 100 NR30 GTRc and 100 NR50 GTRc. All the samples have been treated for 10\({}^{\prime}\) with microwaves.  
Figure 10: SEM pictures of crystal morphology of ZnSt\({}_{2}\) on 0 GTRc(NT)/NR surface: (**a**) (\(\times\)500) and (**b**) (\(\times\)8000).  
The thermal stability of different rubber composites can also be affected by the interaction between natural rubber and devulcanized GTR. Table 1 shows the temperature values obtained from TGA/DTG curves of different NR/GTR car and truck composites. Several intervals can be observed: (a) from 320 \({}^{\circ}\)C to 410 \({}^{\circ}\)C, decomposition of natural rubber (fresh elastomer and NR from GTR); (b) from 410 \({}^{\circ}\)C to 516 \({}^{\circ}\)C, decomposition of synthetic rubber (mainly SBR and other rubber components of GTR) and (c) upwards of 516 \({}^{\circ}\)C, char residue (carbon black and other inorganic materials). The results for each sample show a displacement of temperatures as a function of devulcanization time and type of GTR. As mentioned previously, thermal stability tends to increase slightly with devulcanization time. The maximum values of temperature are 408.5 \({}^{\circ}\)C and 408.1 \({}^{\circ}\)C for the samples of 100 NR50 GTRc5\({}^{\prime}\) and 100 NR50 GTRt5\({}^{\prime}\), respectively. Temperature values assigned to the decomposition of the synthetic components of GTR are more similar for all samples (459 to 460 \({}^{\circ}\)C).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Tm (\({}^{\circ}\)C NR)** & **Tm (\({}^{\circ}\)C SynR)** & **Char Residue** \\ \hline
100 NR & 398.5 & - & 516.0 \\
100 NR10 GTRc & 401.3 & 458.0 & 517.5 \\
100 NR30 GTRc & 402.1 & 459.0 & 517.1 \\
100 NR50 GTRc & 402.9 & 459.3 & 518.3 \\