## 3 Results and Discussions
### Evaluation of Healing Efficiency  
The \(K_{IC}\) values obtained in quasi-static and impact mode for the blend containing 30 wt% of PCL, before and after the healing process, are reported in Figure 11. By looking at the obtained results, the healing efficiency in quasi-static mode is 5.8% and 4.9% for the healing performed at 80 and 100 \({}^{\circ}\)C, respectively. On the other hand, in impact mode, the healing efficiency is 51.5 and 53.0% at the same healing temperatures. Furthermore, the healing efficiency of neat PA6 at 140 \({}^{\circ}\)C is 0%, since only PCL is capable of melting and \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Quasi-Static**} & \multicolumn{2}{c}{**Impact**} \\ \hline
**Sample** & \(K_{IC}\) [MPa m\({}^{\text{1/2}}\)] (a) & \(G_{IC}\) [kJ/m\({}^{\text{2}}\)] (b) & \(K_{IC}\) [MPa m\({}^{\text{1/2}}\)] (c) \\ \hline PA6 & 2.79 \(\pm\) 0.08 & 2.20 \(\pm\) 0.14 & 9.44 \(\pm\) 0.86 \\ PA6\_5 PCL & 3.34 \(\pm\) 0.23 & 3.25 \(\pm\) 0.35 & 9.40 \(\pm\) 0.87 \\ PA6\_10 PCL & 3.08 \(\pm\) 0.31 & 3.33 \(\pm\) 0.45 & 8.77 \(\pm\) 1.03 \\ PA6\_20 PCL & 2.86 \(\pm\) 0.30 & 3.54 \(\pm\) 0.77 & 7.86 \(\pm\) 1.36 \\ PA6\_30 PCL & 2.24 \(\pm\) 0.31 & 2.68 \(\pm\) 0.71 & 7.32 \(\pm\) 0.78 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results describing the fracture behavior of the prepared PA6/PCL blends in quasi-static and impact mode. Figure 10: SEM micrographs of the SENB specimens of the blends tested in quasi-static mode and impact mode. flowing into the crack area during the healing process. Therefore, it is interesting to observe that the overall healing efficiency evaluated in impact mode is significantly higher with respect to that observed in quasi-static mode. The reason behind this discrepancy is related to the different testing speed adopted in these two tests, which produces different fracture surface morphology, as reported in Figure 10. The fracture surface of the specimen tested in quasi-static mode is heavily plastically deformed, thus resulting in a high specific surface area. On the contrary, the fracture surface of the specimens tested in impact mode does not report any deformation, and therefore the specific surface areas are rather low. Being that the PCL domains are evenly distributed in both quasi-static and impact mode samples, if the specific surface area of the crack is higher, then the PCL will fill the cracked area in a more difficult and non-efficient way, as the diffusion of the molten healing agent in the crack zone will be hindered by the presence of a jagged surface. Surprisingly, the healing efficiency obtained for the sample healed at 140 \({}^{\circ}\)C is zero, as the fracture surfaces were not attached after the thermal mending treatment. The differences in the quasi-static and impact mode fracture surfaces, before and after the healing process, are the key to understanding the reason for the different healing efficiency values obtained. Thus, the SEM micrographs of the crack propagation surfaces before and after the healing process in quasi-static mode and in impact mode of the PA6_30 PCL blend are reported in Figure 12. Regardless to the testing speed, the fracture surfaces after the healing process have a much smoother appearance, and the PCL domains are transformed into a thin film, as also reported in the work of [PERSON] et al. on an epoxy/PCL intrinsic self-healing matrix [72]. As previously explained, the samples tested in quasi-static mode present a higher specific surface area with respect to those tested in impact mode. Thus, the PCL layer is not able to fill the crack as efficiently as in the specimens tested in impact mode. Regarding the specimens tested in impact mode, it is possible to see that the PCL layer is covering the majority of the fracture surface, thus efficiently healing the damaged area. On the other hand, by increasing the healing temperature to 140 \({}^{\circ}\)C, something strange happens.