## 3 Results and Discussion
The reasons for the positive effect of the activated carbon addition may be the increase in the degree of polycondensation due to its tremendous specific surface area and reactivity, as well as a thickening effect that usually improves the morphology of the cured bond lines and, consequently, also the strength of manufactured wood-based materials. On the other hand, the lack of further enhancement and the reduction in strength to the level of the reference board may indicate that the loading of 1.5% was too high in this case. Activated carbons demonstrate the tendency to agglomerate [56]. Considering that only a small fraction was used to modify the adhesive, it can be assumed that  
Figure 4: The density of the particleboards: (**a**) average density, (**b**) density profile. Figure 3: Appearance of the laboratory-made particleboards bonded with UF adhesive modified with ACCS. the reason was the agglomeration of the modifier's particles, which negatively affects the quality of the adhesive bonds and hinders the transfer of stresses within the bond [57]. As part of future work, it would be interesting to investigate how a chemical functionalization of the activated carbon surface by the attachment of functional groups, which can improve dispersion within the polymer matrix, could affect the recommended loading range. In the case of the variant containing 1.5% of ACCS, the effect was different from the significant improvement shown by [PERSON] et al. [29]; however, this only proves that many factors, such as, for example, the dimensional fraction of filler affecting the agglomeration [58], can influence the obtained results. The results of TS and WA, indicating the overall water resistance of the manufactured particleboard, are presented in Figure 6. It was found that the applied modification with ACCS affected only the TS results determined after 2 h of soaking (\(p<0.05\)). In the case of variants containing 0.75 and 1%, the recorded value of TS was reduced by approx. 16% compared to the reference particleboard. Considering that this phenomenon was observed only for variants characterized by the improved IB, which is a basic indicator of adhesive performance in the particleboard, the reason for the improved water resistance was most likely the reinforcement of the adhesive bonds [59; 60; 61]. However, it seems that 24 h was enough time for a hydrolytic degradation of the UF adhesive bonds to progress, which led to the average TS values at the reference board level [62; 63]. Nevertheless, the increase in swelling and water absorption observed for the variant containing 1.5% ACCS in the previous study was not observed [29]. This proves again that further research aimed at investigating the effects of factors such as the activated carbon preparation method, activated carbon characteristics, dimensional fraction, homogenization conditions, pressing conditions, and initial properties of adhesive on the expected outcome is still needed. However, it can be concluded that, in this case, the addition of ACCS delayed the degradation of UF adhesive bonds, which was shown by short-term improvement, but had no effect under long-term exposure to water. The results of the formaldehyde content analyses are shown in Figure 7. Statistical analysis showed that the modification had a significant effect on the formaldehyde content (\(p<0.05\)), but the effect varied depending on the amount of added modifier. It was found that a significant reduction was observed only for variants containing 1 and 1.5% of ACCS. Compared to the reference board, the recorded formaldehyde content was lower by approx. 16%. This effect was caused by the ability of activated carbon to adsorb formaldehyde, attributed to its high porosity and specific surface area [46]. A detailed description of the mechanism of formaldehyde adsorption by activated carbon can be found in the recent paper by [PERSON] et al. [18].