# Effect of Variable Conditions of Exposure on the Physical and Mechanical Properties of Blockboards
## 3 Results and Discussion  
### Physical Properties  
Hydrogroscopic surfaces of wood composites as blockboards which are exposed to indoor environment absorb moisture when RH increases and desorb moisture when the RH decreases. This behaviour has influence on the properties of boards. An analysis on the physical transformations of such boards must include the effect of variable environmental conditions of exposure on thickness (t), weight (w) and moisture content (MC). The environmental conditions include the variation of temperature (T) and the relative humidity of air (RH). These parameters were measured twice a day (days*2) for the entire 90-day period of testing and their variations for kitchen and bathroom conditions of exposure are presented in Figure 3.  
The relative humidity (RH) varied between 43% and 88% in the bathroom and between 25% and 64% in the kitchen. The temperature (T) fluctuated from 18.2 \({}^{\circ}\)C to 25.6 \({}^{\circ}\)C in the kitchen and from 18 \({}^{\circ}\)C to 26.4 \({}^{\circ}\)C in the bathroom. Correspondingly, the equilibrium moisture content of panels in the bathroom during exposure was far higher (9.2% to 17.5%) than in the kitchen (6.1% to 11.2%), being influenced by the sudden increases in the relative humidity caused by the activities carried out. Exposure to such a variation of climate led to changes of the thickness (t) value, moisture content (MC) and weight (w) of the boards, as presented in Table 3.  
The density before exposure varied between 387 kg/m\({}^{3}\) and 446 kg/m\({}^{3}\) for panels with veneer (V) faces and between 403 kg/m\({}^{3}\) and 573 kg/m\({}^{3}\) for those with HDF faces. Figure 2: The 15 measuring points of deflection. It can be seen that there were no sudden variations from one month to another; the changes being more evident after three months, especially MC. After three months, the thickness of panels increased by approximately 0.77% (K-V) and 0.79% (K-HDF) and the weight by 1.75% (K-V) and 3.8% (K-HDF), with slight differences between blockboards with veneer and HDF face sheets. MC increased by approximately 17% for V blockboards and by approximately 48% for HDF ones, which recorded, before exposure, the lowest MC. The blockboards with HDF faces exhibited a higher increase of MC after two months of exposure. This can probably be attributed to the moisture homogenisation in the mass of the fibres. \begin{table}
\begin{tabular}{l r r r r r r} \hline \hline  & \multicolumn{3}{c}{**K-V**} & \multicolumn{3}{c}{**K-HDF**} \\  & **t, (mm)** & **w, (g)** & **MC, (\%)** & **t, (mm)** & **w, (g)** & **MC, (\%)** \\ \hline \multirow{2}{*}{Before testing} & 18.11 & 971 & 8.07 & 17.68 & 1293 & 6.7 \\  & (0.09) & (3.5) & (0.3) & (0.09) & (2.5) & (0.02) \\ \multirow{2}{*}{1 month} & 18.13 & 986 & 8.50 & 17.75 & 1315 & 7.1 \\  & (0.06) & (1.2) & (0.4) & (0.11) & (3.9) & (0.4) \\ \multirow{2}{*}{2 month} & 18.15 & 992 & 9.20 & 17.70 & 1320 & 7.7 \\  & (0.06) & (4.4) & (0.4) & (0.09) & (5.3) & (0.3) \\ \multirow{2}{*}{3 month} & 18.25 & 988 & 9.6 & 17.82 & 1342 & 9.9 \\  & (0.09) & (3.9) & (0.5) & (0.11) & (6.0) & (0.9) \\ \hline \end{tabular} Values in the parenthesis are standard deviations.  
\end{table} 
Table 3: Variation of the blockboards’ physical parameters during their exposure in the kitchen conditions (average values recorded for each month). Figure 3: Variation of the environmental parameters: (a) in the kitchen; (b) in the bathroom. The differences between recorded values from one month to another in the case of blockboards tested in the bathroom (Table 4) were more evident than for those exposed in the kitchen. The increases in thickness and weight were 0.64 and 0.52 times higher for V blockboards and 0.9 and 0.21 times higher for HDF blockboards compared to those exposed in the kitchen after 3 months of exposure. The high values of the relative humidity of air recorded in the bathroom (between 50% and 88%) caused more rapid moisture uptake than in the kitchen, even if, after one month, slight decreases were observed in thicknesses and weights.