# Automatic Transmission Fluids in Electrified Transmissions: Compatibility with Elastomers
## 3 Results and Discussion
### Results of Complementary Tests
The thermogravimetric analysis allows us to analyse how the aging process could affect the structure of the elastomers and their thermal stability. Tables 7-9 show the detailed values of the thermogravimetric analysis for each material. Only the fresh and 168 h aged samples results are reported, as no influence of the aging time was found in the long term. Figure 11: TGA (above) and DTGA (below) curves expressed as mass percentage and mass percentage over time, for fresh and 168 h aged FKM. Figure 12: TGA (above) and DTGA (below) curves expressed as mass percentage and mass percentage over time, for fresh and 168 h aged EPDM. Figure 13: TGA (above) and DTGA (below) curves expressed as mass percentage and mass percentage over time, for fresh and 168 h aged silicone. The mechanism of degradation of FKM by dehydrofluorination and chain scission is discussed in previous papers [32]. The major degradation starts at 468 \({}^{\circ}\)C (T\({}_{\text{onset}}\)) and is completed at 503 \({}^{\circ}\)C (T\({}_{\text{endset}}\)), as can be observed in Figure 11 and Table 7. These results are in good agreement with the literature [33; 34]. No noteworthy event was observed at temperatures above the T\({}_{\text{endset}}\). Below, the T\({}_{\text{onset}}\) the loss of mass is about 4% and might be due to the presence of volatile matter in the composition (evaporation of some small organic molecules and other additives used in the fabrication of the rubber and the oils). For the aged samples, the TGA curves follow the same trend (Figure 11). However, the loss of weight is slightly lower (Table 7), especially at low temperatures (below T\({}_{\text{onset}}\)). This difference can be explained by the loss of the volatile components of the elastomer during the heat-aging process, which is consistent with their volume reduction (Figure 1). The thermal degradation process of the EPDM is more complex, as can be seen in Figure 12. The TG curve shows a three-stage mass loss process, and the DTG curve shows the three corresponding peaks at 303, 478, and 707 \({}^{\circ}\)C. The first stage occurred between 236 and 360 \({}^{\circ}\)C and was due to the loss of volatile matter present in the composition of the elastomer [35] and it constituted the main mass degradation (31.5%). The next stage occurred over the 458-490 \({}^{\circ}\)C range, with a 25.52% weight reduction due to the elastomeric matrix degradation. This second stage of thermal decomposition is attributed to the scission of cross-linked EPDM with elimination of carbon dioxide, water, carbon monoxide, methane, and ethane [36]. Finally, the third stage occurred within the 635 to 722 \({}^{\circ}\)C temperature range, with the loss of 2.4% of the initial weight, corresponding to the decomposition of the calcium carbonate additive, whose presence was confirmed by XRD and FTIR. The residual mass was around 40%, which would be composed of mineral components. For aged samples, the TGA curves followed the same trend. However, the weight reduction during the first stage was much greater (Table 8) due to the loss of the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**ATF** & **T\({}_{\text{onset}}\)**[\({}^{\circ}\)C]** & **T\({}_{\text{endset}}\)**[\({}^{\circ}\)C]** & **WL\({}_{\text{Total}}\)**[\%]** & **T\({}_{\text{peak}}\)**[\({}^{\circ}\)C]** \\ \hline Fresh & 468 & 499 & 69.0 & 486 \\ Oil A & 468 & 503 & 66.9 & 489 \\ Oil B & 465 & 503 & 64.2 & 488 \\ Oil C & 468 & 504 & 65.7 & 489 \\ Oil D & 468 & 504 & 64.9 & 489 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: TGA and DTGA data of fresh and 168 h aged FKM.