# Structural Features and Properties' Characterization of
## 3 Results and Discussion
### Rheological Behavior  
The compounds' rheological behavior is important for the estimation of material recycling through melting. Additionally, changes in the patterns of melt flow can help predict the structural features of the resulting polymer systems. The correlations between the storage modulus and dynamic viscosity are shown in Figures 4 and 5.  
The G' curve of the storage modulus steadily went up as the frequency increases, which proves the previously obtained data. Abnormal behavior compared to that of the other samples is seen in sample M20--the G' values in this case are significantly lower. The low G' values may be due to the ESO excess amount, as part of it is no longer able to fully interact with PLA. It is also worth noting that with an increase in the ESO content, the frequency dependence of G' became more pronounced (the graph gets steeper). This can be explained by the increase in the PLA macromolecules' mobility.  
Figure 4: Correlation between G’ and frequency.  
Figure 5: Correlation between viscosity and frequency.  
An analysis of the complex viscosity's relation to frequency in all samples revealed no plateau-like areas, indicating a typical non-Newtonian behavior of melts [26]. As the ESO content increased, the viscosity values dropped. This is especially noticeable in the M20 sample. This can also be explained by the excess amount of ESO, which, in this case, acts as a lubricant while the melt flows.  
Figure 6 shows the relationship between the storage modulus and the applied strain. The G' values naturally decrease as the ESO content rises; i.e., with the introduction of oil, the material becomes more viscous and less elastic. One should note the difference in the change G' with an increase in the deformation amplitude. All ESO-containing samples demonstrated a sharp drop in G' in the 20-40% deformation range. This can be explained by stronger PLA-NR interaction in the presence of ESO. The ESO-induced interface structures, characterized by weak interaction energy, break down almost immediately once low-amplitude deformations are applied. However, the very fact of the presence of such structures makes it possible to surmise that PLA-NR compatibility increases in the presence of ESO. This is consistent with previous studies [12; 13], where it was found that epoxy groups have a positive effect on the PLA-NR compatibility. The M0 sample (no ESO) has no such structures; therefore, the relation of G' and deformation amplitude, in this case, looks like a low-pitch (almost horizontal) curve without pronounced drops in G' values.  
The relationship plot of \(\eta\)\" (imaginary viscosity) and \(\eta^{\prime}\) (real viscosity), known as the Cole-Cole plot, is yet another tool that can be used to study the properties of polymer compounds' structures [30]. These plots are known to take the shape of sloping curves, a semicircle, or a plateau depending on a compound's morphology and the degree of components interaction [31]. The slope ratio (tgA) of the Cole-Cole plot in the range of small \(\eta^{\prime}\) values describes the degree of polymers' compatibility. The tgA-ESO content relationship is given in Figure 7.  
Figure 6: Correlation between G’ and deformation.  
Higher tgA values describe greater compatibility of the mix components. The figure shows that the increase in the ESO content by more than 10 mass parts causes a much steeper tgA drop and, as a result, a greater worsening of the PLA-NR compatibility.