# Preparation of Piezo-Resistive Materials by Combination of PP, SEBS and Graphene
## 3 Results and Discussion
### Mechanical Properties  
The iPP/SEBS blend and nanocomposites prepared via both routes were subjected to tensile testing measurements. The Young's modulus, elongation at break, tensile strength, and toughness values are listed in Table 2 (see stress-strain curves in Figure S2). Firstly, the iPP/SEBS blend prepared by R1 outperformed in stiffness (Young's modulus), deformation capacity (elongation at break) and toughness when compared to the same sample prepared by R2. This can be explained by the greater homogeneity of the composite and the smaller SEBS domains when formulated via R1, in agreement with the SEM data. It is worth highlighting, that the latter sample exhibits extremely large deformations and shows the phenomenon of strain hardening with an ultimate stress of 25.8 MPa (Figure S2A). This effect can be related to the more uniform and superior stretching behavior, toughness, and ductility achieved in the more homogeneous sample. As a result, the iPP molecules can align in the direction of the load at larger strains. The Young's modulus gradually increases with the addition of G and GPP fillers for both routes, as typically observed for graphene nanocomposites. The addition of the fillers counteracts the improvement of the elongation capacity achieved by the SEBS additive, this being more marked for samples prepared by R1. On the contrary, the decrease in the tensile strength derived from the elastomeric component is better balanced with the addition of G and GPP when the composite is prepared via R2. Especially interesting is the variation of toughness, since it was maximum in binary mixtures prepared by R1 and becomes almost null when the fillers are added. However, in the case of R2, toughness also decreases with the addition of graphene albeit maintaining reasonably good values compared with iPP. Within R2 approach, the best stiffness/toughness relationship was found for the sample with unmodified graphene. Although the better dispersion of GPP in the iPP matrix is expected to improve properties, this effect can be counteracted by the formation of non-cylindrical and larger SEBS domains (as seen by SEM). In addition, the location of the rigid filler at the SEBS/iPP interfaces \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **Sample** & **T\({}_{1}\) (\({}^{\circ}\)C)** & **T\({}_{\text{max}}\) (\({}^{\circ}\)C)** & **Residue (\%)** \\ \hline \multirow{3}{*}{R1} & iPP/SEBS & 384.5 & 453.6 & 0.5 \\  & iPP/SEBS/G & 401.9 & 468.7 & 4.8 * \\  & iPP/SEBS/GPP & 400.1 & 467.4 & 5.0 * \\ \hline \multirow{3}{*}{R2} & iPP/SEBS & 376.1 & 450.0 & 0.6 \\  & iPP/SEBS/G & 400.5 & 464.9 & 4.9 * \\ \cline{1-1}  & iPP/SEBS/GPP & 400.7 & 469.7 & 4.8 * \\ \hline \hline \end{tabular}  
* T\({}_{i}\): Initial degradation temperature obtained at 2% weight loss, T\({}_{\text{max}}\): Temperature of maximum weight loss rate,
* corrected value with blank sample residue.  
\end{table} 
Table 1: Characteristic degradation temperatures and char residues obtained from the thermogravimetric analysis (TGA). Figure 4: Thermogravimetric (TG) (**A**) and first derivative thermogravimetric (DTG) (**B**) curves of films prepared from iPP/SEBS composites with and without G and GPP filler obtained through the SoM and SoM/SSM formulation routes. could alter the elastomeric properties of SEBS, which translate into lower values of toughness and elongation at break. This effect is primarily observed for the R1, where the homogenous solution of polymers and the filler dispersion may favor both \(\pi\)-\(\pi\) as well as olefinic interactions simultaneously. It is also worth noting that the addition of the GPP filler generates the material with the greatest resistance to deformation if prepared via R2, where the interfacial interaction between the polyolefins from the matrix and filler are likely to reinforce their adhesion (8% improvement compared to the optimum value for the iPP/SEBS composite).