## 3 Results and Discussions
### Mechanical Properties  
Figure 9a-c reports the trends of the elastic modulus (E), of the ultimate tensile strength (UTS), and of the elongation at break (\(\epsilon_{b}\)) of all the prepared blends, obtained from quasi-static tensile tests. It is worth mentioning that two different behaviors can be identified during the test. PA6 and PA6/PCL samples do not present any yielding and have limited strain at break values, while the neat PCL shows an evident yielding and elevated elongation at break values (representative stress-strain curves were not reported for brevity). Generally speaking, the mechanical properties of the produced blends tend to decrease by increasing the PCL content. The elastic modulus decreases from 3.6 GPa for neat PA6 to 2.0 GPa for the PA6_30 PCL sample (relative drop of 44%), the UTS decreases from 72.3 MPa for neat PA6 to 39.2 MPa for the PA6_30 PCL blend (relative drop of 46%), and the elongation at break decreases from 6.6% for neat PA6 to 5.1% for the PA6_30 PCL blend (relative drop of 23%). Several phenomena tend to influence the mechanical properties of an immiscible polymer blend, such as cavitation during the deformation process, the limited \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & \(T_{\text{TS}}\)[40] [T-C] & \(T_{\text{TS}}\)[40] [T-C] & \(T_{\text{D}}\) PCL[40] [T-C] & \(m_{\text{D}}\) PCL[40] [T-C] & \(T_{\text{D}}\) PA6[40] [T-C] & \(m_{\text{D}}\) PA6[40] [T-C] \\ \hline PA6 & 326.5 & 398.3 & - & - & 461.5 & 32.9 \\ PA6_5 PCL & 278.0 & 390.0 & 419.5 & 81.1 & 459.3 & 25.4 \\ PA6_10 PCL & 251.3 & 391.5 & 432.3 & 62.3 & 468.7 & 18.2 \\ PA6_20 PCL & 283.7 & 390.2 & 423.7 & 58.7 & 463.1 & 9.0 \\ PA6_30 PCL & 227.8 & 384.3 & 416.8 & 52.9 & 457.3 & 5.7 \\ PCL & 249.3 & 389.2 & 420.2 & 48.2 & - & - \\ \hline \hline \end{tabular} \({}^{a)}\)\(T_{1\%}\) = temperature associated to a mass loss of 1%, \({}^{b)}\)\(T_{5\%}\)= temperature associated to a mass loss of 5%, \({}^{c)}\)\(T_{\text{D}}\)\(PCL\) = degradation temperature of PCL, \({}^{d)}\)\(m_{\text{D}}\)\(PCL\) = residual mass associated to the degradation temperature of PCL, \({}^{e)}\)\(T_{\text{D}}\) PA6= degradation temperature of PA6, and \({}^{d)}\)\(m_{\text{D}}\)\(PA6\) = residual mass associated to the degradation temperature of PA6.  
\end{table} 
Table 2: Results of the TGA analysis performed on the prepared PA6/PCL blends. Figure 8: TGA tests on the prepared PA6/PCL blends. (a) Residual mass and (b) mass loss derivative curves. mechanical properties of the dispersed phase, and the limited interfacial adhesion between the constituents [64]. The immiscibility of the produced blends was demonstrated in several analyses, i.e., the Cole-Cole plot (Figure 3a), in which different relaxation processes can be observed, and the SEM micrographs (Figure 5), in which the limited interfacial adhesion between PA6 and PCL can be observed. Thus, the limited interaction between the constituents, together with the lower mechanical properties of the dispersed phase, leads to a general decrease in the mechanical properties of these blends. The mechanical properties of the prepared blends were modeled through the expressions reported in Equations (2)-(4). It can be seen that the trend of the elastic modulus of the blends is not correctly modeled by the used models, and in particular, it is possible to see that the ME model fails to predict the stiffness of the blends at limited PCL amounts. Both the UTS and the \(\varepsilon_{b}\) values of the prepared blends are overestimated by the three models considered, and the reason could be the very low adhesion between the two constituents. The results reported in Table 3 describe the fracture behavior of the prepared blends in quasi-static mode and impact mode and in particular, the trends of the KIC and of the GIC as a function of the volume fraction of PCL.