# Alkylimidazolic Ionic Liquids Absorption and Diffusion in Wood
## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & \multicolumn{4}{c}{**Wood-Related Properties**} \\ \cline{3-6}
**II-Related Properties** & & & \multicolumn{4}{c}{**(Dependent Variable)**} \\ \cline{3-6}
**(Independent Variable)** & **Statistical Analysis Parameters 1 ** & **Sprace** & & **Beech** \\ \cline{3-6}  & & & \(w_{IL,eq}\) & \(\Delta V\) & \(w_{IL,eq}\) & \(\Delta V\) \\ \hline  & Normality & \(p\) & 0.140 & 0.365 & 0.261 & 0.554 \\ \cline{2-6} \(\gamma\) & Correlation & \(p\) & \(-0.031\) & \(-0.258\) & \(-0.118\) & 0.017 \\ \cline{2-6}  & & \(R\) & 0.953 & 0.621 & 0.824 & 0.890 \\ \hline  & Normality & \(p\) & 0.145 & 0.332 & 0.282 & 0.483 \\ \cline{2-6} \(\eta\) & Correlation & \(p\) & 0.099 & \(-0.306\) & 0.018 & \(-0.368\) \\ \cline{2-6}  & & \(r\) & \(-0.851\) & \(-0.555\) & \(-0.729\) & \(-0.473\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Statistical analysis of the dependence between selected wood-related properties (dependent variables) and ionic liquid-related properties (independent variables). equilibrium sorption is effectively reached after 8 to 10 h (Figure 2a), while for water it can take several days. In the case of water diffusion, generally, a two-step sorption kinetic can be observed, with the first step occurring at a higher rate, related to the filling and moisture saturation of capillaries and cavities near the surface of the wood, followed by a slow ongoing uptake related to water diffusion into the wood. As diffusion proceeds, the difference in chemical potential between the sorbed water and the water from the wood cellular walls decreases, and the water uptake rate also decreases [34; 35]. Ionic liquids' high affinity for cellulose and lignin determines their high uptake rate, which remains unchanged in the diffusional step until the wood fiber saturation and the reaching of the sorption equilibrium. This high affinity is economically appealing, as wood is swollen and saturated with IL at room temperature at a higher rate than in the case of waterborne wood preservatives, despite their much higher viscosity. The permeability of both spruce (softwood) and beech (hardwood) for the ILs was observed as reasonably similar (Figure 2b,c), as is the case in the reference literature for moisture diffusion [36; 37; 38]. The diffusion in the longitudinal direction is the highest, most likely due to the more significant number of pits (spruce) or wood vessels (beech) in this direction [37]. Figure 3a,c presents the ATR-FTIR spectra of beech wood and spruce wood treated with the alkylimidazolium chloride ILs, as these ILs promote the most significant interactions within the wood matrix. Since the IR absorption bands of the ILs can overlap with those of wood, the second derivative spectra were performed to discern the effect of ILs on the lignocellulosic. Figure 3b,d represents the second derivative of the spectra from Figure 3a,c, respectively. Figure 2: (a) Sorption kinetic of 1-butyl-3-methylimidazolium chloride IL into spruce wood; (b) diffusion coefficients for various ILs in spruce wood; and (c) diffusion coefficients for various ILs in beech wood. All the studied ILs promote physical interactions with the wood components (cellulose, hemicellulose, and lignin) [39], mainly related to intermolecular hydrogen bonds breaking and restructuring in both types of wood (shifting of the -OH stretching band centered at \(\sim\)3330 cm\({}^{-1}\) to lower wavenumbers [40]. The -OH band maximum shifting is more pronounced as the length of the lateral alkyl chain of the cation increases, i.e., \(\text{HMIM}^{+}>\text{BMIM}^{+}>\text{EMIM}^{+}\) and as the hydrophilicity of the anion increases and \(\text{CI}^{-}>\text{CH}_{3}\text{COO}^{-}>\text{BF}_{4}^{-}\) (Figure 3a,c).