## 3 Results and Discussion
### Analysis of Mechanical Properties  
The mechanical properties of the samples, specifically, Young's modulus, tensile strength, and elongation at break, are shown in Figure 2.  
The average value of Young's modulus for the resin samples immediately after printing is 365 MPa and almost doubles to a value of 701 MPa after one month. The addition of solvent causes a decrease in the modulus, which reaches a minimum value of 135 MPa for samples made from a resin-35% alcohol solution measured immediately after manufacturing the samples. After one month, the samples showed a significant increase in modulus compared to the values obtained for the samples immediately after printing, but with a trend of decreasing values with increasing alcohol concentration. No results were given for specimens with an alcohol concentration of 35% after one month due to their too-extensive deformation preventing the specimens from being placed without destruction in the jaws of the testing machine. Almost the same characteristics of changes in values can be seen for tensile strength, where the maximum strength value of 18 MPa was obtained with pure resin samples after one month and the minimum strength value of 3 MPa was characterized by samples with the highest alcohol concentration of 35% tested immediately after receipt. In the case of relative elongation at break, it can be observed that the elongation for the pure resin samples was almost unchanged over time at about 13%, while the addition of alcohol at a concentration of 15% reduced the elongation to 5%, which increased to about 13% after one month. For the samples with 25 and 35% alcohol, the elongation was 4-5% and did not increase after one month to a value comparable to the elongation of the pure resin samples, in contrast to the samples with 15% alcohol. Figure 3 shows the course of the representative curves obtained during the static tensile testing of the samples. It can be seen that the resin and resin-15% alcohol samples show plastic flow after one month without a clear yield point. The other samples show mainly elastic properties before tensile rupture of the material. The reasons for the described changes in the strength parameters of the samples can be found in the effect of the solvent on the radical polymerization process of the resin. The phenomenon is known; transferring a polymer chain to a solvent, including alcohol solvent, by abstracting the solvent atom and deactivation of the active center of the macroradical, forms a polymer chain of lower molecular weight than in the case of polymerization without solvent [26]. In the case of ethanol used as a solvent, the radicals were most likely formed by detaching a hydrogen atom from the secondary carbon atom carrying the hydroxyl group [27] due to the higher O-H bond energy of the hydroxyl group (BDE of approximately 437. 6 kJ/mol\({}^{-1}\)) and C-H in the methyl group (BDE approximately 410.0 kJ/mol\({}^{-1}\)) than the C-H bond energy for the carbon carrying the hydroxyl group (BDE approximately 396.6 kJ/mol\({}^{-1}\)) [28; 29; 30]. The obtained radicals, due to the lack of steric hindrances, are  
Figure 2: Mechanical properties of samples related to solvent amount and time of measurement. more unstable and reactive than radicals formed from resin components, which are particles that are more extended and have functional groups or branching. The introduction of particles that form highly reactive radicals into the radical polymerization process can result in an acceleration of the kinetics of the process while leading to the formation of lower molecular weight network fragments. Lower molecular weight, meanwhile, affects mechanical properties by decreasing Young's modulus and mechanical strength, which is the case with the alcohol-resin samples. Furthermore, solvent addition can reduce the formation of cross-links by attaching alcohol molecules to the cross-linker, also deteriorating the strength properties [31].