# Prediction of Mechanical Performance of Acetylated MDF at Different Humid Conditions
## 2 Materials and Methods
### Experimental  
#### 2.2.1 Dimensional Changes  
The relative changes in length and thickness of the samples were determined in between two equilibrium conditions. The increases in length and thickness due to swelling were measured from 65% to 85% RH in adsorption (first regime), while the reductions in length and thickness due to shrinkage  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **Properties Measured** & \begin{tabular}{c} **Dimensions** \\ **[mm\({}^{3}\)]** \\ \end{tabular} & \begin{tabular}{c} **Sample** \\ **Number** \\ \end{tabular} & \
\begin{tabular}{c} **Standard** \\ **Followed** \\ \end{tabular} \\ \hline \multirow{4}{*}{Physical properties} & Moisture content & \(50\times 50\times 18\) & 15 & EN 322 [33] \\  & Density & \(50\times 50\times 18\) & 15 & EN 323 [34] \\  & Dimensional changes & \(300\times 50\times 18\) & 10 & EN 318 [35] \\  & Thickness swelling & \(50\times 50\times 18\) & 5 & EN 317 [36] \\  & Accelerated aging & \(300\times 70\times 18\) & 5 & \\ \hline \hline
\begin{tabular}{c} Mechanical \\ properties \\ \end{tabular} & Internal bonding & \(50\times 50\times 18\) & 15 & EN 319 [37] \\  & Three-point bending & \(300\times 36\times 18\) & 15 & EN 310 [38] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Dimensions (length \(\times\) width \(\times\) thickness) of samples used for measuring different physical and mechanical properties of Medite Tricoya® medium density fiberboard (MDF) samples.  
were measured from 65% to 35% RH in desorption (second regime), according to the standard EN 318 [35]. The samples were exposed to different RH levels until acclimatized at two regimes. The first regime consisted of dimensional changes among consecutive RHs 35%, 65% and 85% at 20 \({}^{\circ}\)C constant temperature, whilst the second regime consisted of consecutive RHs in the reverse order, i.e., 85%, 65% and 35%, at 20 \({}^{\circ}\)C constant temperature.  
Relative expansion and contraction sample's length were calculated using the formulae below:  
\[\delta l_{65,85}\ (\text{mm/m})=1000\times(l_{85}-l_{65})/l_{65} \tag{1}\]  
\[\delta l_{65,35}\ (\text{mm/m})=1000\times(l_{35}-l_{65})/l_{65} \tag{2}\]  
where \(\delta l_{65,85}\ (\text{mm/m})\) is the relative increase in length due to swelling of sample's length after RH change from 65% to 85%, based on the length \(l\ (\text{mm})\) measured at 65% RH and 85% RH; \(\delta l_{65,35}\ (\text{mm/m})\) is the relative reduction in thickness due to the shrinkage sample's length after RH change from 65% to 35%, based on the length \(l\ (\text{mm})\) measured at 65% RH and 35% RH.  
Similar to the calculations of relative change in the sample's length, thickness swelling and shrinkage properties were calculated as follows:  
\[\delta t_{65,85}\ (\%)=100\times(t_{85}-t_{65})/t_{65} \tag{3}\]  
\[\delta t_{65,35}\ (\%)=100\times(t_{35}-t_{65})/t_{65} \tag{4}\]  
where \(\delta t_{65,85}\ (\%)\) is the relative increase in sample's thickness due to swelling after RH change from 65% to 85%, based on the thickness \(t\ (\text{mm})\) measured at 65% RH and 85% RH; \(\delta t_{65,35}\ (\%)\) is the reduction of the sample's thickness due to shrinkage after RH change from 65% to 35%, based on the thickness \(t\ (\text{mm})\) measured at 65% RH and 35% RH.