## 3 Results and Discussions  
### Rheological Properties  
A complete rheological investigation was carried out on the produced blends in order to understand their processability and the miscibility conditions [37]. Figure 2a,b report the results obtained from the dynamic rheological measurements on the prepared blends in terms of dynamic moduli, i.e., storage and loss modulus, and complex viscosity. The low-frequency \(G^{\prime}\) values of the PA6_xPCL samples are slightly higher with respect to their individual components, especially in the case of the PA6_30 PCL blend. In addition, by looking at the \(G^{\prime}\) plots, it can be observed that by increasing the PCL concentration, the storage modulus tends to increase. The presence of small PCL domains within the PA6 matrix could result in a superior energy storage capacity of the blends with respect to the neat constituents [38]. On the other hand, \(G^{\prime\prime}\) values also tend to increase with the PCL content. Figure 2b reports the complex viscosity curves of all the produced blends, and the classic shear thinning behavior of polymeric materials can be detected [39], with a \(\eta^{*}\) decrease at elevated frequencies [40]. The value of complex viscosity of the neat PA6 is significantly lower in comparison to that of the neat PCL over the whole frequency range, and an increase in the complex viscosity of the blends can be registered with the PCL content. It is possible to infer that the presence of PCL domains inside the PA6 matrix tends to hinder the motion of PA6 macromolecules at the molten state [41].  
Figure 1: Schematic representation of the device used for the thermal mending process.  
One of the possible ways to investigate the morphological changes in polymer blends at the molten state is through the so-called Cole-Cole plots. These plots represent the description of the viscoelastic properties of polymer blends characterized by high relaxation time distributions, thus highlighting phase separation phenomena within the blends [42]. In the Cole-Cole plot, the imaginary viscosity (\(\eta^{\prime\prime}\)) is reported as a function of real viscosity (\(\eta^{\prime}\)), and in doing so, two different outcomes can be observed. If a smooth and semicircular arc of a curve is present, a good compatibility between the constituents of the polymer blend in the molten state can be predicted. On the other hand, if two different circular arcs or tails can be observed, the existence of phase heterogeneity and immiscibility within the blend can be demonstrated [43]. Another possible way of investigating the miscibility conditions of polymer blends is through the Han plot, in which the log G\({}^{\prime}\) versus log G\({}^{\prime\prime}\) are reported, generally resulting in a linear correlation [44]. The compatibility of the polymer blend can be demonstrated if the slope of the obtained curves at different relative concentrations of the constituents is the same [45; 46]. On the contrary, if these curves show different slopes, then the analyzed blend is considered to be immiscible [47; 48]. Figure 3a reports the Cole-Cole plots of the neat matrices and of their blends. The relaxation process of both neat PA6 and neat PCL is described by a single circular arc, while by increasing the PCL fraction in the blends, the appearance of two-stage relaxation phenomena can be observed, thus proving the immiscibility of the prepared blends [49]. Furthermore, Figure 3b reports the Han plot of neat PA6, neat PCL, and of their blends. From these plots, it is possible to highlight a linear region at elevated G\({}^{\prime\prime}\) values, but the slope of these lines is systematically different, thus confirming that these blends can be considered immiscible [50; 51].