# Thermal and Mechanical Behavior of Elastomers Incorporated with Thermoregulating Microcapsules
## 3 Results and Discussion
### Thermal Stability  
The thermal stability of PU elastomers depends on multiple factors, such as the proportion between soft and hard segments, the chain extensor type and the [NCO]/[OH] molar ratio [18; 20; 25]. Figure 6 shows the thermogravimetric results of the mSD-(LDPE-EVA-RT27) and pure paraffin (Rubitherm(R)RT27) used in the microcapsules' synthesis and all the synthesized elastomers. Figure 5: Porosity (**a**) and density (**b**) of the elastomers with different mSD-(LDPE-EVA-RT27) contents and [NCO]/[OH] molar ratios. Figure 6: Thermogravimetric analyses (**a**,**b**) and their DTGs (**c**,**d**) of the synthesized elastomers, mSD-(LDPE-EVA-RT27) and the pure paraffin. Peaks I = HS degradation; Peak II = SS degradation; Peak III = high molecular weight reticulated segment degradation; Peak VI = allophanates degradation. As can be seen in Figure 6, the pure paraffin and the paraffin from mSD-(LDPE.EVA-RT27) were completely evaporated at 210 \({}^{\circ}\)C, whereas the shell material of the microcapsules was degraded at 480 \({}^{\circ}\)C. On the other hand, the thermal degradation of the polyurethane elastomers was a complex process with three different thermal degradation steps. The first degradation step corresponding with urethane bond decomposition from the hard segments (peak I of the DTG elastomer curves) occurred between 300 and 380 \({}^{\circ}\)C. The second degradation step appeared between 380 and 500 \({}^{\circ}\)C, and this can be attributed to the soft segment degradation (peak II). Finally, there was a third small step from 550 \({}^{\circ}\)C, which was due to the presence of reticulated segments of a high molecular weight. It is worth pointing out that all the elastomers were stable up to 280 \({}^{\circ}\)C, and therefore, the paraffin evaporation was delayed, probably evaporating while the urethane bond degradation took place. This could be due to the immersion of the microcapsules in the polymer matrix acting as a protected barrier, forming a form-stable material. Aside from that, it can be noticed that for the [NCO]/[OH] molar ratio of 1.05, there was a residue with a maximum value of 10 wt.% for the case without PCMs. On the contrary, elastomers from the [NCO]/[OH] molar ratio of 1.1 presented a fourth degradation peak and absence of residue, probably because of the excess of -NCO reacting with the urethane groups at high temperatures and forming allophanates that decomposed around 600 \({}^{\circ}\)C [26]. From the TGA results, the experimental weight loss corresponding to the soft and hard segments of the elastomers (SS and HS, respectively) and the mSD-(LDPE.EVA-RT27) shell for each one of the synthesized elastomers was determined and compared to the theoretical expected values. Figure 7 shows the experimental and theoretical weight loss for the SS, HS and mSD-(LDPE.EVA-RT27) shells, depending on the microcapsules content and the [NCO]/[OH] molar ratio. The theoretical values were estimated from the mass contents of the microcapsules, their compositions and the mass of polyurethane components added in the elastomer synthesis recipe. It can be observed in Figure 7 that the HS proportion in the elastomers increased with the microcapsule content up to the case of 15 wt.% mSD-(LDPE.EVA-RT27), probably due to the fact that paraffin degradation also occurred at this degradation step, as was mentioned before. However, for the case of 20 wt.% mSD-(LDPE.EVA-RT27), the elastomers presented a HS percentage value similar to that of the pure elastomers. This can be attributed to poor homogenous elastomers, in which the particles would tend to form agglomerates. Aside from that, the HS experimental contents were higher than the theoretical ones. Again,  
Figure 7: Experimental and theoretical weight loss for the SS, HS and microcapsule shells, depending on the mSD-(LDPE.EVA-RT27) content, for [NCO]/[OH] molar ratios of (**a**) 1.05 and (**b**) 1.1. The straight lines indicate the linear trends of the weight loss. this was partially due to the paraffin degradation in that step.