# Prediction of Mechanical Performance of Acetylated MDF at Different Humid Conditions
## 3 Results and Discussion
### Mechanical Properties  
Table 4 shows MOEstat, MORstat and IB properties of parallel and perpendicular samples from Medite Tricoya(r) MDF conditioned at dry, standard and wet conditions. With the increase of RH from 35 to 65%, the average MOEstat and MORstat reduction of Medite Tricoya(r) samples was 8% and 10%, respectively. When the RH was further raised from 65% to 85%, reduction of those properties was respectively 37% and 20%. Higher humidity environment had a detrimental effect on the MOEstat and MORstat and IB strength values for both sample types. Mechanical properties like MOEstat and MORstat measure the elastic behavior and resistance to bending, respectively, and are important properties when MDF is placed under load. Aforementioned properties determine largely the applicability of MDF as a structural component in furniture or other constructions. Those properties also depend on the sample properties, i.e., sanding direction (parallel or perpendicular), density, moisture content and type of MDF [2; 5; 43]. Dimensional stability is a good indication of the acetylation effect. However, moisture content had a great influence on the strength properties of both types of MDF samples. Significant reductions in MOEstat, MORstat and IB strength values were observed with an increase in RH (Table 4). These findings are in agreement with the  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Dry, 35\% RH**} & \multicolumn{3}{c}{**Standard, 65\% RH**} & \multicolumn{3}{c}{**Wet, 85\% RH**} \\ \cline{2-10}  
results found in previous studies [2; 43]. The decrease in such properties at increasing RH level can be attributed to the separation of fibers resulting from the thickness swell of the panel materials [44]. Differences in the static bending properties were also found between parallel and perpendicular samples, and especially at the dry condition these differences were statistically significant. In general, MOEstat and MORstat values were higher in parallel samples compared to perpendicular samples (see Table 4). Lower bending strength and stiffness values of perpendicular samples in MDF and other wood-based panels have been reported previously [26]. Figure 2 shows the linear regressions that determine how well the MORstat are related with MOEstat values in parallel and perpendicular samples at different humid conditions. Statistical analysis showed strong positive and significant relationships (\(p<0.05\)) for both sample directions (parallel and perpendicular) at varying humidity levels. Strong correlation between bending strength and modulus of elasticity is known for wood-based panels [45]. When linear regression analyses were performed by separating humid condition, very poor and insignificant relationships were observed. In the parallel samples, the coefficients of determination (R\({}^{2}\)) were 0.08 and 0.39 at 65% and 85% RH, respectively; whilst in the perpendicular samples, those values were, respectively, 0.20 and 0.25. However, in a dry condition (35% RH), significant relationships (\(p<0.05\)) were observed, and R\({}^{2}\) values were 0.85 and 0.88 in parallel and perpendicular samples, respectively. Previous findings also showed higher correlation coefficients at lower moisture content levels for wood-based panels [46; 47]. A positive and significant relationship (\(p<0.05\)) between MORstat and IB was also observed (Figure 3). As shown in Table 4, Medite Tricoya(r) samples had the highest IB strength at 35% RH. With the increase of RH from 35 to 65%, the average IB strength reduction of Medite Tricoya(r) samples was 20%. When the RH was further raised from 65% to 85%, reduction of IB strength was 27%. UV radiation causes photochemical degradation mainly in lignin polymers of the cell walls. UV light in combination with water plays a major role in such type of weathering. When lignin is degraded, water washes away degraded products and subsequently loosens the surface fibers to erode.