# Utilization of Partially Liquefied Bark for Production of Particleboards
## 3 Results and Discussion
### Performance of the Particleboard Containing PLB  
The mechanical properties (i.e., MOE, MOR, IB, and tensile strength) of the particleboard panels containing PLB in the presence of MUF or not are presented in Figure 6. The non-MUF bonded boards \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **T\({}_{\textbf{onset}}\) (\({}^{\circ}\)C)** & **T\({}_{\textbf{max1}}\) (\({}^{\circ}\)C)** & **T\({}_{\textbf{max2}}\) (\({}^{\circ}\)C)** & **T\({}_{\textbf{offset}}\) (\({}^{\circ}\)C)** \\ \hline Bark & 219 & 361 & – & 428 \\ PLB & 152 & 215 & 397 & 495 \\ Purified PLB & 148 & 218 & 403 & 495 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thermal degradation properties of bark, PLB, and purified PLB. Figure 5: (a) Equilibrium moisture content (EMC) of bark, PLB and purified PLB samples exposed to increasing water vapor from relative humidity (RH) of 0 to 95%; (b) moisture increment during adsorption of bark, PLB, and purified PLB samples. containing 4.7% and 9.1% PLB (boards I and II) did not show any cohesion, and, thus, easily decomposed during cutting as illustrated in Figure 7. The MOR, MOE, and tensile strength values of the non-MUF boards were improved by increasing the PLB content. The particleboard containing wood particles and the highest amount of PLB (board IV) exhibited the highest values. A significant increment in the MOE, MOR and tensile strength of the non-MUF boards occurred when the PLB content increased from 9.1% to 20%. At least 20% of PLB was required for the non-MUF panels to be able to perform the IB test. It should be noted that the mechanical property values of all the non-MUF boards (I, II, III, and IV) were very low and did not meet the requirement of particleboard for interior uses in dry conditions according to EN 312:2010. Figure 6: Average MOE (**a**), MOR (**b**), IB (**c**), and tensile strength (**d**) of particleboard containing partially liquefied bark, with or without MUF adhesives. Values labelled with the same letter (small for MUF boards, and capital for non-MUF boards) are not statistically different from each other (ANOVA, [PERSON]’s HSD test, \(p<0.05\)). Error bars represent standard deviations. Figure 7: Particleboard samples containing 4.7%, 9.1%, 20%, and 33.3% (I–IV in order) partially liquefied bark without using MUF adhesives. The mechanical properties of the particleboard were apparently changed by the synergistic effect of MUF adhesives and PLB. The MOE, MOR, and IB strength of the boards bonded with MUF adhesives increased by adding 4.7% and 9.1% PLB (boards VI and VII), and they were significantly higher than the reference one, board V. However, the differences between MOE, MOR, and IB values of the boards with 4.7% and 9.1% of PLB, i.e., boards VI and VII, were not statistically significant. Further, increasing the PLB content to 20% and 33.3% drastically decreases the MOE, MOR, and IB strength of the boards. This might be attributed to the decreasing proportion of the wood particles in the board content, which led to a decrease in the density (as shown in Table 1). The higher PLB amount may have also increased the inhomogeneity of the boards, and thus disturbed the equal distribution of the applied stresses during the mechanical tests. The results of mechanical properties showed that up to 20% of PLB can be used in the particleboard content to produce boards that meet the minimum requirements for interior use in dry conditions according to EN 312:2010, in terms of MOR, MOE, and IB values that are, respectively, 13, 1800, and 0.40 N/mm\({}^{2}\). The tensile strength parallel to surface was negatively affected by increasing the PLB content in the MUF-bonded boards. When over 20% PLB was applied, the tensile strength of the boards (VIII, IX) was lower than half of the strength of the reference (V). As a conclusion, 9.1% of PLB loading should be allowed for producing particleboard with good overall mechanical properties.