## 3 Results and Discussion
### Mechanical Properties  
#### 3.3.1 Tensile Strength  
Tensile strength tests of composites in the PLA matrix were carried out for both a horizontal (blue on the graphs) and vertical (green) orientation, as shown in Figure 8 These fittings were obtained using the L-FDM method in 3D printing. The red lines marked on the graphs indicate the values of the reference samples, unmodified PLA printed both horizontally and vertically. Figure 8A,B display the parameters gathered from samples passed through an alcohol-filled reservoir, while Figure 8C,D show data obtained from  
Figure 7: Optical microscope images of cross-sections of the printed bars; (**A**)—PLA/MeOH; (**B**)—PLA/EuOH; (**C**)—PLA/i-PrOH; (**D**)—PLA/Bn OH; (**E**)—PLA/CyOH; (**F**)—PLA/n-BuOH; (**G**)—PLA ref. bars produced by passing the filament through a reservoir containing silanes and silicone oils dissolved in methanol. The tensile strength values for horizontally printed samples (Figure 8A) decreased as the alcohol chain length increased. The PLA/MeOH sample printed horizontally had the highest values, with an increase of 18.3% compared to the reference sample. MeOH simple structure enables it to penetrate effectively between the polymer chains, thereby modifying the polymer matrix more effectively. This effect is not observed with cyclic alcohols, resulting in the lowest strength value among the tested samples, which is shown by the Pla/BnOH alcohol-modified sample at 35.99 [MPa]. Benzyl alcohol dissolves esters and has a high boiling point (205 \({}^{\circ}\)C), allowing it to enter the extruder with the polymer and enhance the effect of polymer alcoholysis. Microscopic images also show that with the increase in the length of the alcohol chain, the number of defects (air gaps) increases, which results in a decrease in tensile strength. Graphs 8C and 8D show test results for samples modified with solutions of silanes in methyl alcohol. Literature data indicate an improvement in the mechanical properties of PLA with the use of silane crosslinking (Figure 9) [14]. The highest increase in tensile strength was observed for the PLA/BRB294/MeOH sample, and compared to the reference, it is 18.94%. The strain at break also increased, which indicates the plasticizing nature of the additive. BRB 176 contains an amine functional group in its structure, capable  
Figure 8: Mechanical properties: (**A**) tensile strength for PLA/alcohols; (**B**) elongation at break for PLA/alcohols; (**C**) tensile strength for PLA/alcohol/silanes; (**D**) elongation at break for PLA/alcohol/silanes. of producing weak interactions with the polylactide matrix. An increase in the tensile strength of shapes printed in a horizontal orientation was observed. However, a completely opposite relationship was observed for fittings printed in a vertical orientation. The adhesion between the layers of the PLA/BRB 176/MeOH sample deteriorated significantly. Probably, this phenomenon could be caused by a change in the rheological properties of PLA and a reduced amount of dispensed material during the printing process, which could have caused a reduction in the surface of the connecting layer [15]. The observed changes in mechanical parameters are also a clear confirmation of the effectiveness of introducing the modifier with the L-FDM technique. The increase in the strength of samples with the addition of organosilicon compounds occurs due to their crosslinking with polyesters, as shown in Figure 9.  
Similar tests were carried out for samples on the PET-G matrix (Figure 10). The red lines marked on the graphs indicate the values of the reference sample, unmodified PET-G. Most of the samples show an increase in tensile strength and an increase in elongation at break, which may indicate the plasticizing effect of methanol on PETG. Similar to samples printed with PLA, BRB 294 has the greatest impact on tensile strength, resulting in an increase of 53.73% over the reference sample. BRB 294 is the most optimal modifier for use in L-FDM printing to improve the strength properties of PETG prints.