# Prediction of Mechanical Performance of Acetylated MDF at Different Humid Conditions
## 3 Results and Discussion
### Mechanical Properties
However, as expected, \(\text{MOE}_{\text{dyn}}\) values were higher than the static values approximately by 40%. Wood-based panels contain a significant number of glued interfaces, and such a difference is generally explained by the different rates of stresses applied in the dynamic and static tests [52]. The differences between the \(\text{MOE}_{\text{dyn}}\) and \(\text{MOE}_{\text{stat}}\) values were higher at a higher RH. It was 33%, 37% and 49% higher at 35%, 65% and 85% RH conditions, respectively. This is because moisture affects the stress-wave properties for wood-based panels, as they can swell considerably during moisture uptake. The swelling often leads to bond failures and to changes of their internal structure, and as a result, to a decrease of stress wave velocity with the increase in panel moisture content [26]. Acoustic tools have been used quite successfully to predict \(\text{MOE}_{\text{stat}}\) and \(\text{MOR}_{\text{stat}}\)[26; 27; 53]. Table 5 shows the multiple regression model summary results. Overall, linear and significant relationships (\(p<0.05\)) of \(\text{MOE}_{\text{stat}}\) and \(\text{MOR}_{\text{stat}}\) with \(\text{MOE}_{\text{dyn}}\) were observed at different humid conditions. It was noted that \(\text{R}^{2}\) values were slightly higher between \(\text{MOE}_{\text{dyn}}\) and \(\text{MOE}_{\text{stat}}\) than those between \(\text{MOE}_{\text{dyn}}\) and \(\text{MOR}_{\text{stat}}\). The comparison between the experimental and predicted values is shown in Figure 6. The result indicates that the predicted values are very close to the experimental values. F-values for all models (\(\text{MOE}_{\text{stat}}\) and \(\text{MOR}_{\text{stat}}\) in parallel and perpendicular samples) were highly significant at the 0.05 level (Table 5). Statistical analysis showed that \(\text{MOE}_{\text{dyn}}\) and RH can be used as predictors of \(\text{MOE}_{\text{stat}}\) and \(\text{MOR}_{\text{stat}}\) of MDF samples. The results also indicated that \(\text{MOE}_{\text{stat}}\) and \(\text{MOR}_{\text{stat}}\) have a positive relationship with \(\text{MOE}_{\text{dyn}}\). Figure 5: Dynamic modulus of elasticity (\(\text{MOE}_{\text{dyn}}\)) of Medite Tricoya® MDF samples at different relative humidity levels measured by the acoustic resonance method. Error bars represent 95% confidence intervals for the means. * Significant differences between parallel and perpendicular samples as determined by two-sample t-test at the 0.05 level. NS, non-significant. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{\(\text{MOE}_{\text{stat}}\)} & \multicolumn{2}{c}{\(\text{MOR}_{\text{stat}}\)} \\ \cline{2-5}  & **Parallel** & **Perpendicular** & **Parallel** & **Perpendicular** \\ \hline \(\text{R}^{2}\) & 0.987 & 0.969 & 0.966 & 0.925 \\ Adjusted \(\text{R}^{2}\) & 0.970 & 0.964 & 0.960 & 0.913 \\ Standard error & 99.484 & 97.717 & 1.020 & 1.175 \\ Intercept & \(-412.519\) & 883.65 & 26.822 & 28.071 \\ RH coefficient & \(-5.101\) & \(-11.624\) & \(-0.140\) & \(-0.120\) \\ \(\text{MOE}_{\text{dyn}}\) coefficient & 0.784 & 0.573 & 0.004 & 0.003 \\ F & 227.009 & 187.664 & 169.889 & 74.404 \\ Significance F * & 0.000 & 0.000 & 0.000 & 0.000 \\ \hline \hline \end{tabular}
* Significant at the 0.05 level.  
\end{table} 
Table 5: Model summary of regression statistics for \(\text{MOE}_{\text{stat}}\) and \(\text{MOR}_{\text{stat}}\) prediction.