# Thermal and Mechanical Behavior of Elastomers Incorporated with Thermoregulating Microcapsules
## 3 Results and Discussion
### Elastomer Structure and Filler Distribution  
Once the proper chemical structures of the synthesized elastomers were confirmed, their morphologies were observed by SEM for further understanding of their physical and mechanical properties. Figure 3 shows two examples of the typical filler distribution in matrix that were very similar in the rest of the samples, and Figure 4 shows the SEM pictures of the different synthesized elastomer matrices.  
Figure 4: SEM pictures at 6000\(\times\) magnification of the synthesized elastomer matrices with different mSD-(LDPE-EVA-RT27) contents and [NCO]/[OH] values of 1.05 and 1.1.  
Figure 3: SEM photos of filler distributions for the E-1.1-20 at 200\(\times\) magnification (**a**) and for the E-1.05-15 at 3000\(\times\) magnification (**b**).  
The filler distribution in the polymer matrix was not totally homogeneous, as can be seen in Figure 3. Many of the microcapsules were well distributed, as shown in Figure 3b, and some others were agglomerated, as can be seen in Figure 3a. The rest of the synthesized elastomers also presented mSD-(LDPE:EVA-RT27) distributed for the whole polymer matrix with some agglomeration points.  
As can be seen in Figure 4, the elastomers presented a structure of polyurethane derived from aromatic diisocyanates consisting of a net of spherical microparticles [21; 22]. Aside from that, most particles presented a homogeneous size, except for some bigger particles. The most accurate study of the influence of the mSD-(LDPE:EVA-RT27) content and of the [NCO]/[OH] molar ratio on the particle size was carried out by using Motic Plus software (see Table 2).  
According to the results, the addition of mSD-(LDPE:EVA-RT27) reduced the particle size of the polymeric matrix and improved the sample structure homogeneity, since lower standard deviations were obtained. The particle size of the polymeric matrix structure was at a minimum for E-1.05-15 and E-1.1-10. Thus, the presence of MC increased the nucleation point during polymer formation, reducing the particle size of the polymeric matrix up to 10-15 wt.%. Nevertheless, from this point, the effect of the agglomeration due to the increase of the sample viscosity stabilized or even increased the particle size of the polymeric matrix [23].  
On the other hand, the effect of the elastomer structure on the porosity and density was also analyzed, and both effects are shown in Figure 5.  
As can be seen, the higher the MC content, the lower the sample porosity, probably due to the reduction of the particle size of the polymeric matrix, the presence of the MC in the structure and the increase of the reactive mixture viscosity. On the other hand, despite the porosity decrease, the density also decreased, since the mSD-(LDPE:EVA-RT27) density was 0.866 g/cm\({}^{3}\)[24], 26.7% lower than the net elastomer density. In the case of elastomer E-1.05, the density decrease was almost linearly dependent on the mSD-(LDPE:EVA-RT27) content. A similar tendency was observed up to an MC content of 10 wt.% for the elastomer E-1.1. Nevertheless, from that point, higher densities than those obtained for the composites from a [NCO]/[OH] molar ratio of 1.05 were observed, possibly due to the excess of isocyanate.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Elastomer** & **Average Particle Size (\(\mu\)m)** & **Maximum Value(\(\mu\)m)** & **Minimum Value(\(\mu\)m)** \\ \hline E-1.05-0 & 2.640 \(\pm\) 0.409 & 3.689 & 0.785 \\ \hline E-1.05-5 & 2.049 \(\pm\) 0.227 & 3.759 & 0.689 \\ \hline E-1.05-10 & 1.735 \(\pm\) 0.210 & 2.388 & 1.271 \\ \hline E-1.05-15 & 1.617 \(\pm\) 0.283 & 2.288 & 0.684 \\ \hline E-1.05-20 & 1.896 \(\pm\) 0.346 & 2.537 & 1.022 \\ \hline E-1.1-0 & 2.220 \(\pm\) 0.696 & 4.862 & 1.449 \\ \hline E-1.1-5 & 1.893 \(\pm\) 0.212 & 2.480 & 1.473 \\ \hline E-1.1-10 & 1.693 \(\pm\) 0.193 & 2.230 & 1.201 \\ \hline E-1.1-15 & 1.868 \(\pm\) 0.234 & 2.483 & 1.164 \\ \hline E-1.1-20 & 1.734 \(\pm\) 0.295 & 3.110 & 1.081 \\ \hline \end{tabular}
\end{table}
Table 2: Average particle size of the elastomer polymeric matrices.