## 3 Results and Discussion
### Moisture Absorption of the Samples  
The initial weights of the samples and the respective tolerances are shown in Table 2. Table 3 then expresses the average absolute increase in weight of the individual sets of samples after 60 days of testing, including the basic descriptive statistics. The average relative weight gain was also determined. Weight losses due to delamination of the coatings were neglected, as this phenomenon only occurred to a limited extent and, moreover, until the end of the degradation testing. Furthermore, as can be seen from Table 2, the weight of the coating is negligible compared with the weight of the sample. On the basis of the measurements carried out, it can be stated that any of the mentioned forms of secondary post-processing reduces the absorption of the moisture in the samples, thus ultimately helping to extend their service life. It is clear from the above results that it is most suitable to implement post-processing in the form of a coating application, namely a synthetic coating or epoxy resin. From the point of view of the unsuitable mechanical properties of the epoxy layer [35], however, a synthetic coating clearly appears to be a more universal coating. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & & **Quantity** & \\ \hline
**Type of PP** & **AM, g** & **D, g2** & **SD, g** & **CV, \%** & **RML \%** \\ \hline
**CS** & 41.98 & 0.1243 & 0.3526 & 0.840 & 2.29 \\
**HT** & 41.72 & 0.0941 & 0.3068 & 0.735 & 1.53 \\
**ER** & 44.19 & 0.1959 & 0.4426 & 1.002 & 0.94 \\
**SC** & 42.23 & 0.1498 & 0.3870 & 0.917 & 0.76 \\
**WBC** & 42.68 & 0.1711 & 0.4136 & 0.969 & 1.67 \\
**WPP (rPET-G)** & 42.43 & 0.1848 & 0.4299 & 1.013 & 3.34 \\
**WPP (PET-G)** & 42.47 & 0.1037 & 0.3220 & 0.758 & 3.21 \\ \hline \hline \end{tabular}  
* PP—Post-processing; CS—Chemical smoothing HT—Heat treatment; ER—Epoxy resin; SC—Synthetics coating; WBC—Water-based coating; WPP—Without post-processing; AM—Arithmetic mean; D—Dispersion; SD—Standard deviation; CV—Coefficient of variance; RMI—Relative material increase.  
\end{table} 
Table 3: Evaluation of the moisture absorption of the individual samples after 60 degradation cycles. The significantly higher value of moisture absorption in the case of the water-based coating is due to its delamination in the final phase of testing. This phenomenon was visually detected after approximately 50 cycles. Premature delamination of the coating can be justified by the application of the so-called self-priming coating (\"2 in 1\") since the absence of a primer generally leads to lower adhesion of the created barrier [39]. Furthermore, it is a deficiency in the form of the formation of pores and cracks during their application. This statement was also proven in Figure 2f. However, the aforementioned deficiency can be partially eliminated by applying a larger number of thinner coatings, since it has been found that coatings composed of several layers are more durable than a single coating of the same thickness. Also, for ecological reasons, it is advisable to use water-based coating materials [48; 49; 50]. It can also be stated that, from a longer-term point of view, it is more advantageous to perform heat treatment of the component than chemical smoothing. The reason is the homogeneous cross-section of the annealed part. The chemically smoothed sample has mechanical properties at its core, or shortcomings, comparable to the benchmark. For this reason, immediately after perforation of the smoothed surface, the component degrades at a similar rate. In the case of chemical smoothing, higher moisture absorption can be caused by insufficient smoothing of surface pores. The salt solution begins to penetrate through these defects to the undersurface layers shortly after the beginning of degradation testing (compared with the other technologies of post-processing), which results in increased moisture absorbtion.