# Some of the Physical and Mechanical Properties of
## 3 Results and Discussion
### Surface Quality Analysis  
Table 3 presents the surface roughness and CAs of the test samples. The fine particleboard had a smoother surface (6.20 \(\upmu\)m (R\({}_{a}\)), 7.79 \(\upmu\)m (R\({}_{q}\)), and 30.85 \(\upmu\)m (R\({}_{z}\))) and higher CA at 0 s (104.4\({}^{\circ}\)) and k (0.011), compared with the coarse particleboard, which had a rougher surface (7.48 \(\upmu\)m (R\({}_{a}\)), 9.02 \(\upmu\)m (R\({}_{q}\)), and 32.48 \(\upmu\)m (R\({}_{z}\))), lower CA (94.13\({}^{\circ}\)), and k (0.021). The representative example for measurement of the CA of a water droplet is shown in Figure 5. Dynamic contact angle measurements were plotted to show the evolution of contact angle overtime (Figure 6). The equilibrium CA (0e) of the regression model fit found that the contact angle exhibited an exponential decay becoming fairly stable for time (t) > 30 s. The average 0e of the fine particleboard is 88.52 s, while the coarse particleboard is 63.91 s. The reducing contact angle is related to a dynamic wetting process [28,44].  
Figure 4: Screw withdrawal resistance of the sample. Values followed by the same letters are statistically not different at \(p<0.05\).  
Certain parameters including particle compaction, fine screen particles, lower extractive content, higher press time, and moisture content play an important role in increasing  
Figure 5: Representative measurement of the contact angle of a water droplet (**a**) the first time the water touches the surface of the board (t = 0 s); (**b**) as the water is absorbed (t = 60 s); (**c**) the static contact angle on fine and coarse _D. asper_ bamboo particleboard (t = 180 s).  
Figure 6: The dynamic wetting process as shown by the contact angle (\({}^{\circ}\)) with time.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Particleboard** & **R\({}_{\textbf{a}}\) (\(\mu\)m)** & **R\({}_{\textbf{q}}\) (\(\mu\)m)** & **R\({}_{\textbf{z}}\) (\(\mu\)m)** & **CA (\({}^{\circ}\)) at 0 s** & **k** \\ \hline Fine particles & 6.20 \({}^{\text{a}}\) & 7.79 \({}^{\text{a}}\) & 30.85 \({}^{\text{a}}\) & 104.04 \({}^{\text{a}}\) & 0.011 \({}^{\text{a}}\) \\  & (\(\pm\)0.17) & (\(\pm\)0.28) & (\(\pm\)1.66) & (\(\pm\)15.25) & 0.011 \({}^{\text{a}}\) \\ Coarse particles & 7.48 \({}^{\text{b}}\) & 9.02 \({}^{\text{b}}\) & 32.48 \({}^{\text{a}}\) & 94.13 \({}^{\text{b}}\) & 0.021 \({}^{\text{a}}\) \\  & (\(\pm\)0.47) & (\(\pm\)0.86) & (\(\pm\)4.18) & (\(\pm\)10.90) & 0.021 \({}^{\text{a}}\) \\ \hline \hline \end{tabular} \(\text{R}_{\text{a}}\): Arithmetical mean roughness; R\({}_{\text{q}}\): The root mean square value of the ordinate values; R\({}_{\text{g}}\): The maximum profile height; CA: Contact angle; k: Constant rate of change of the contact angle. Symbol \(\pm\) in bracket denotes standard deviation values. Numbers followed by the same letters are not significantly different.  
\end{table}
Table 3: Average surface roughness and contact angles of _D. asper_ particleboards.  
the smoothness of the surface [45; 46]. The current study found that the higher the surface roughness or the coarser the particleboard, the lower the CA. In a previous study, wood species with a porous structure was found to have a higher surface roughness [47; 48]. In terms of the coarser particleboard, the lower CA indicated perfect wetting, which means better hydrophilicity. It was also pointed by the k value, where the coarser particleboard had higher k values compared to the fine particleboard. The k corresponds to the easiness of the liquid spreads and penetrates [28; 46]. This parameter is important in a gluing and coating system. A study by [PERSON] [48] found that a surface of laminated bamboo revealed the CA was about 60\({}^{\circ}\) at 0 s and the starting table for time was more than 20 s in a wetting process. The time difference of reducing contact angle was due to the ability of water as a polar liquid to spread on the surface bamboo and be absorbed into the bamboo cellular structure [48].