# Mechanical Properties and Formaldehyde Release of Particleboard Made with Lignin-Based Adhesives
## 3 Results and Discussions
### Mechanical Properties  
The results of the mechanical testing of the experimental panels are presented in Table 5, where the values in the parentheses represent the standard deviations. As a general remark, the mechanical properties of the particleboard panels are improved for the modified magnesium lignocellulosic oxidation and further, by adding cross-linkers, such as PMDI and glucose.  
The values of MOR and MOE are comparable with results obtained for composite panels produced from waste fibers bonded with magnesium lignocellulosic [47]. The comparison between the mechanical performances of the experimental panels and the results of the modulus of elasticity (MOE), bending strength (MOR) and internal bond, (IB) in relation with the limits imposed by EN 312: 2004 [57] for the panel P2 type (designed for the indoor application, including furniture), is presented in Figure 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Panel Type** & **MOE 1 (N/mm2)** & **MOR 1 (N/mm2)** & **IB 1 (N/mm2)** \\ \hline L 20 & 1847 (133) & 8.1 (0.94) & 0.10 (0.03) \\ LO 20 & 2783 (319) & 10.6 (0.76) & 0.12 (0.03) \\ LO 20 P1 & 2526 (185) & 11.0 (0.34) & 0.22 (0.03) \\ LO 20 P2 & 2778 (239) & 13.0 (0.47) & 0.31 (0.05) \\ LO 20 P3 & 2931(89) & 15.3 (0.73) & 0.41 (0.04) \\ LO 20 P1G & 3123 (152) & 13.3 (0.74) & 0.38 (0.06) \\ LO 20 P2G & 3320 (112) & 14.3 (0.58) & 0.48 (0.07) \\ \hline \hline \end{tabular}
\end{table}
Table 5: Experimental results on the mechanical properties of the tested panels.  
Figure 2: FTIR analysis for oxidized LIGNEX MG F and cross-linked adhesives with PMDI and glucose.  
As seen in Figure 3a, MOE increased 1.8 times for the particleboard made with oxidized lignocellulosic, 2% PMDI and glucose wt.1% of the lignocellulosic weight (LO 20 P2G), compared to the particleboard made with magnesium lignocellulosic powder as adhesive (L 20). All panels have MOE values above the limit of 1600 N/mm\({}^{2}\) imposed by the standard EN 323 [60] for the P2 type panels.  
The statistical analysis of the data using Minitab 18 software has shown the normal distribution of the MOR, MOE and IB values. All \(p\)-values resulted in the analysis were much less than 0.05, indicating that the influence of the tested lignin-based adhesives was statistically significant for all the investigated mechanical properties.  
The results of bending strength (MOR) presented in Figure 3b show increased values when modified lignocellulosic by oxidation is used as adhesive, and the values increased more with the increase of cross-linkers (PMDI and glucose) content. The MOR limit imposed by standard [57] for the P2 type panels (13 N/mm\({}^{2}\)) was met by panels made with adhesives composed of oxidized lignocellulosic and PMDI (2% and 3%, respectively) (panels LO 20 P2 and LO 20 P3, respectively), and also by panels with the addition of glucose and PMDI (1% and 2%) cross-linkers to oxidized lignocellulosic adhesive (panels LO 20 P1G and LO 20 P2G, respectively).  
The same increased trend of MOR values was observed also for the internal bond strength (IB), as seen in Figure 3b. The limit of 0.35 N/mm\({}^{2}\) imposed by standard [57] was met for this property only for panels LO 20 P3, LO 20 P1G and LO 20 P2G. The values of the internal bond strength are for these panels 3.8 to 4.8 times higher than the value for the panel made with magnesium lignocellulosic powder as adhesive.  
The results of the mechanical properties show that only the particleboards with oxidized magnesium lignocellulosic and the addition of cross-linkers, namely PMDI (3%), or PMDI (1% and 2%) and glucose (1% of the magnesium lignocellulosic content) met the requirements of the panels designed for indoor application, furniture included.