## 3 Results and Discussion
6% [29]; however, this may depend on the properties of the carbon itself, the fraction used, etc. Besides the water absorption mentioned before, the addition of any organic or inorganic filler, even in small quantities, leads to a thickening of the UF adhesive, which usually also means an increase in viscosity [53]. Moreover, it was found that the addition of activated carbon did not significantly affect the pH of the adhesive mixtures. The appearance of the produced particleboards is shown in Figure 3. No effects from the addition of activated carbon up to 1.5% were observed. On the contrary, in the case of the greater carbon loadings, the obtained boards darken and become grayer [29]. Therefore, with no side effects compromising the aesthetics of the material, this can be considered as the advantage of smaller loadings. Density is one of the most important parameters of particleboard. It can noticeably affect the vast majority of a board's properties and can be used to control its targeted functional properties [54]. As shown in Figure 4a, the addition of activated carbon had no significant effect on the obtained density value (\(p>0.05\)). The average result for each variant was very close to the assumption, and the difference did not exceed 5 kg/m\({}^{3}\). Moreover, the most common U-shaped course of the density profile was observed for manufactured particleboards (Figure 4b). This phenomenon is highly beneficial because denser subsurface layers contribute to a more efficient transfer of both tensile and compressive stresses during bending [55]. However, the implemented adhesive modification did not affect the density profile. \begin{table}
\begin{tabular}{c c c c} \hline
**Activated Carbon** & **Gel Time (s)** & **Viscosity (mPa-s)** & **pH** \\
**Content (\%)** & & & \\ \hline
0.00 & 92 \(\pm\) 4 \({}^{\text{b}}\) & 282.7 \(\pm\) 3.5 \({}^{\text{a}}\) & 6.21 \(\pm\) 0.04 \({}^{\text{a}}\) \\
0.25 & 95 \(\pm\) 4 \({}^{\text{b}}\) & 285.0 \(\pm\) 2.6 \({}^{\text{a}}\) & 6.20 \(\pm\) 0.01 \({}^{\text{a}}\) \\
0.50 & 94 \(\pm\) 7 \({}^{\text{b}}\) & 302.3 \(\pm\) 3.5 \({}^{\text{b}}\) & 6.21 \(\pm\) 0.03 \({}^{\text{a}}\) \\
0.75 & 99 \(\pm\) 5 \({}^{\text{b}}\) & 305.0 \(\pm\) 2.6 \({}^{\text{b}}\) & 6.20 \(\pm\) 0.03 \({}^{\text{a}}\) \\
1.00 & 94 \(\pm\) 5 \({}^{\text{b}}\) & 314.0 \(\pm\) 6.2 \({}^{\text{c}}\) & 6.20 \(\pm\) 0.02 \({}^{\text{a}}\) \\
1.50 & 79 \(\pm\) 2 \({}^{\text{a}}\) & 314.3 \(\pm\) 4.0 \({}^{\text{c}}\) & 6.21 \(\pm\) 0.03 \({}^{\text{a}}\) \\ \hline \end{tabular} a, b, c...—homogeneous groups according to the Tukey test.  
\end{table} 
Table 2: Properties of UF adhesive mixtures modified with ACCS. The results of mechanical properties such as IB, MOR, and MOE are summarized in Figure 5. The outcomes of the conducted analysis have shown that the modification of UF affected each strength parameter in a statistically significant way (\(p<0.05\)). Based on the IB results, it was found that the addition of ACCS in amounts of 0.25 and 0.5% did not cause significant changes. Perhaps, in this case, the loading was too small to affect the strength of the entire board. Markedly, the increase in the ACCS content to 0.75 and 1% resulted in a statistically significant improvement. In these cases, the average value was higher by approx. 25% compared to the non-modified board. However, a further increase in the loading to 1.5% resulted in a decrease in IB to the level of the reference board. The analysis of the average MOR and MOE values revealed a similar tendency. Participants characterized by increased IB also exhibited improved MOR and MOE values, respectively. The reason was most likely the enhancement of the bonding quality caused by the introduction of ACCS.