## 3 Results and Discussion
### Measurement of the Tensile Strength  
Table 4 and Figure 3 express the results of the tensile test. The graphical dependence of the tensile strength on the type of post-processing is additionally supplemented by the average relative weight gain caused by the moisture absorption. All static tests were carried out on a ZDM 5/51 universal testing machine. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & & & & & & \\ \hline \multicolumn{8}{c}{**Quantity**} \\ \hline \multicolumn{8}{c}{**Testing Phase**} \\ \hline \multirow{2}{*}{**Type of PP**} & \multicolumn{2}{c}{**AM, MPa**} & \multicolumn{2}{c}{**D, MPa2**} & \multicolumn{2}{c}{**SD, MPa**} & \multicolumn{2}{c}{**CV, \%**} \\ \cline{2-9}  & **Before** & **After** & **Before** & **After** & **Before** & **After** & **Before** & **After** \\ \hline \multirow{2}{*}{**CS**} & 43.59 & 41.03 & 1.9044 & 4.1616 & 1.38 & 2.04 & 3.17 & 4.97 \\  & HT & 47.13 & 44.29 & 2.3716 & 5.1076 & 1.54 & 2.26 & 3.27 & 5.10 \\  & ER & 43.05 & 41.99 & 2.1316 & 2.8900 & 1.46 & 1.70 & 3.39 & 4.05 \\  & SC & 42.87 & 42.06 & 0.9216 & 1.2544 & 0.96 & 1.12 & 2.24 & 2.66 \\  & WBC & 42.98 & 41.05 & 1.0816 & 3.4596 & 1.04 & 1.86 & 2.42 & 4.53 \\  & WPP (rPET-G) & 42.79 & 38.46 & 1.6384 & 2.1904 & 1.28 & 1.48 & 2.99 & 3.85 \\  & WPP (PET-G) & 44.18 & 40.37 & 1.0404 & 4.6656 & 1.02 & 2.16 & 2.31 & 5.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Tensile test evaluation (before and after 60 degradation cycles). The tensile strength, or general mechanical properties, need to be evaluated on two levels. First of all, it is a comparison of the recycled material and the primary material (without post-processing). In this regard, the initial PET-G polymer can be characterized as more advantageous due to its higher tensile strength (before and after the degradation test). Statistically, however, this is a difference of approximately 4%, which is a very small value. For reasons of ecology, the recycled material can therefore be clearly recommended, and any requirement for higher strength can be compensated for, for example, by increasing the critical cross-section of the given component. The authors [45] also dealt with the evaluation of the tensile strength of PET-G and rPET-G and reached similar results. Specifically, the average tensile strength value of rPET-G was 2 MPa lower than that of PET-G. The second level is the evaluation of the post-processing adjustments. Here, heat treatment appears to be the most suitable implementation. In this case, even the average values (after the degradation test) are comparable to the standard PET-G (before the degradation test). The improvement of the mechanical properties before the degradation test compensates for the deficiency in the form of higher moisture absorption. Taking the size of the standard deviations into account, the remaining variants of the post-processing can be evaluated as comparable. It was also statistically proven by the experiment that, with a sample cross section of 18 mm\({}^{2}\), 60 degradation cycles have an effect on reducing the tensile strength of the standards. Due to the size of the error bars, this cannot be stated in the case of the post-processing adjustments. Figure 4 shows examples of the nature of the failure of the individual samples, which always occurred in different areas (even within one set). In general, therefore, it is not possible to confirm or refute the effect of the post-processing on the creation of a specific critical point of the sample failure. However, the closest thing to this hypothesis is the chemical smoothing method. Figure 3: Tensile strength before and after the degradation (arithmetic mean \(\pm\) standard deviation): CS—Chemical smoothing; HT—Heat treatment; ER—Epoxy resin; SC—Synthetics coating; WBC—Water-based coating; rPET-G—Recycled (without post-processing); PET-G—Virgin plastic (without post-processing).