## 3 Results and Discussion
### Concerning the Dissolution Tests of the PLA Specimens
For all other specimens with pre-existing precipitated particles, the amount of precipitation increased. On the fourth day, the amount of precipitation in all cases further increased; no other significant change was observed. On the fifth day, the powder-like structure of the precipitation, in the case of GYP immersed in the 12.55 pH solution, turned into a crystal-like structure parallel to the direction of the printing direction of the specimens. On the sixth day, a crystal-like solution appeared in all cases immersed in the 12 pH solution and all cases immersed in the 12.55 pH solution except the ESD specimen. In the case of ENG, HI, and GYP specimens, precipitation occurred as tiny, floating particles in both solutions; in the case of GYP immersed in the 12.55 pH solution, the precipitation also occurred in the wall of the measuring cup as well as in the solution. On the seventh day, white crystal-like precipitation occurred in ESD immersed in the 12.55 pH solution. In addition, the amount of precipitation increased in all other test samples and the solutions. Figure 15 shows the occurrence and the changing of the precipitation during the observation of the dissolution tests. Figure 14: Fading of the color of the HI specimen immersed into the 12.55 pH solution with a small amount of white precipitation on day 7. The remaining time of the dissolution tests was monitored weekly, where changes in the surface of the test specimens and the amount of solution remaining were observed. Despite covering the solution, the amount of the solution decreased. Table 7 shows the percentage reduction in the solutions from the original initial volume of 50 mL, all compared to the previous volume. The most significant decrease in solution amount, in percentage terms, was observed in the GYP specimens, where the material absorbed half of the solution in both the 12.55 and 12 pH solutions. Observing Table 7, it can be seen clearly that the next value after the GYP percentage was a decreased value (50%), while 40% was observed for the rest of the solutions with pH 12.55. This was followed by the HI sample of the pH 12 solution with a 30% decrease, followed by the combination of ABS, ESD, and ENG samples with a 20% decrease. By the second week, the amount of precipitation had noticeably increased, while the amount of solution had decreased in all samples but not to the same extent. In the case of pH 12 solutions, the most significant amount of decrease was in the case of the HI and ENG specimens at 45%, followed by 40% in the case of ESD, then 30% with ABS, and a 25% decrease with GYP. By the third week, both the pH 12 and pH 12.55 solutions ran out of solution from the GYP and HI test samples. By the fourth week, no liquid remained in either solution for HI and GYP, and only the amount of white precipitate increased. In \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **Week 1** & **Week 2** & **Week 3** & **Week 4** \\ \hline pH 12.55 solutions & & & & \\ \hline ESD & 40 & 30 & 25 & 5 \\ ENG & 40 & 25 & 25 & 10 \\ HI & 40 & 35 & 25 & 0 \\ ABS & 40 & 30 & 20 & 10 \\ GYP & 50 & 25 & 25 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Decrease in the amount of solution at pH 12.55 and pH 12 during the four-week period. Figure 15: Occurrence of the precipitation by the time observed at the HI specimens. contrast, at pH 12, 15% of the solution remained for ABS and 5% for ENG and ESD. For the same materials, the liquid was also retained in the pH 12.55 solution: 10% for ABS and ENG and 5% for ESD. As the solutions slowly ran out in the beakers, the white precipitate-like material on the test samples increased. Figure 16 shows the formation and weekly spread of white substance and on the HI specimen immersed in the pH 12.5 solution. As shown in Figure 16, the white precipitate is widely spread on the surface of the specimen; what is interesting about the location of the white material is that it started to form on the line where the specimen touched the solution, and the HI material started to fade.