## 3 Results and Discussion
### The Properties of the Manufactured Foil
This range is typical for fast-cooled PET resin, which was confirmed by other studies [35; 42; 43]. However, it should be pointed out that, again none of the results indicate any significant structural differences that could be caused by the used additives. Undoubtedly, this is a situation confirming that the characteristics of the extruder foils, including its structural properties, have not changed significantly after the reactive extrusion process. However, previously observed changes in the haze parameter for samples with the addition of PMDA are usually associated with changes in the morphology of the crystalline phase, which should be visible in DSC studies [39; 44]. The lack of significant differences in the results for the materials subjected to DSC analysis does not always mean that the structural changes are not present. In many cases, the changes in the signal characteristics overlap, which means that the information on the DSC curve, important from the point of view of analysis, coincides with the signal for a more pronounced transition. In particular, this problem is important for the results of the 1 st stage of heating, when the thermo-mechanical history of the sample has a great influence on the course of the DSC signals. After remelting, the cooling stage of the DSC test revealed more pronounced differences in thermal characteristics, especially for PMDA-modified samples. The discussed change concerns the visible shift in the exothermic peak position. For reference PET sample (VD) the crystallization peak maximum was at around 181 \({}^{\circ}\)C, while for most samples, it ranges between 183 \({}^{\circ}\)C and 190 \({}^{\circ}\)C. The observed increase can be related to a small nucleation effect, which is usually the case with even a small amount of additives or impurities [35]. A more interesting change was observed for PMDA-modified samples, where the crystallization exotherm was shifted to lower temperatures. Regardless of the used matrix, a drop in the crystallization temperature of about 10 \({}^{\circ}\)C was observed for all samples. This phenomenon appears to be related to the efficiency of the reactive extrusion process. The correlation of the efficiency of the reactive extrusion process with \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Peak Position**} & \multicolumn{2}{c}{**Enthalpy, AH**} & \multirow{2}{*}{\
\begin{tabular}{c} **Crystallinity** \\ **(Content) \({}^{*}\)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Crystallization** \\ **Peak** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} } \\ \cline{2-2} \cline{5-6}  & **Cold Cryst.** & **Melting** & **Cold Cryst.** & **Melting** & **(\%)** & **(\%)** \\ \hline VD & 137.7 & 251.8 & 33.9 & 49.5 & 11.1 (31.8) & 180.8 \\ VD-B1 & 132.0 & 250.4 & 34.1 & 50.8 & 11.9 (32.8) & 183.5 \\ VD-M1 & 129.6 & 250.5 & 29.4 & 45.4 & 11.4 (28.2) & 169.9 \\ V & 131.3 & 253.2 & 30.4 & 48.7 & 13.0 (27.4) & 183.9 \\ V-B1 & 128.9 & 248.3 & 30.8 & 46.4 & 11.2 (27.3) & 187.3 \\ V-M1 & 133.0 & 250.3 & 31.1 & 47.2 & 11.5 (28.0) & 172.6 \\ MIX & 130.7 & 253.1 & 32.1 & 49.8 & 12.7 (28.3) & 188.4 \\ MIX-B1 & 130.0 & 252.7 & 31.7 & 48.0 & 11.7 (28.7) & 190.1 \\ MIX-M1 & 128.5 & 250.8 & 30.3 & 47.2 & 12.0 (27.8) & 168.1 \\ \hline \hline \end{tabular}  
* The values in the brackets are calculated from the 2 nd heating stage.  
\end{table} 
Table 2: The thermal properties obtained from the DSC plot analysis. the phase transition change during crystallization has already been thoroughly described in other articles, in particular for chain extenders based on epoxy groups [45; 46; 47; 48]. In the discussed case, the result indicates a very similar mechanism, where as a result of the addition of PDMA, the molecular weight of the processed PET increases, resulting in a change in the mobility of macromolecules and a reduction in the kinetics of the formation of lamellar structures of the crystalline phase [49].