# Physico-Mechanical Properties of Particleboards Produced from Macadamia Nutshell and Gum Arabic
## 3 Results
### Physical Properties  
The one-way ANOVA analysis shown in Table 4 depicted that the density presented a significant level of difference between the four treatments (F3,8 = 347.97; \(p\) < 0.05). Density values ranged between 817 kg/m\({}^{3}\) for T1 and 1219 kg/m\({}^{3}\) for T4. It showed that increasing the proportion of gum Arabic-adhesive in the mixture increased particleboard density. The highest density in T4 can be also explained by the high specific gravity of gum Arabic and macadamia nutshell and the balanced proportion of the two materials in the mixing design. On the other hand, the presence of voids in treatment T1 and T2 can explain the low-density values compared to T3 and T4.  
A similar result was found by [PERSON] et al. [13] by mixing 80% of macadamia nutshell and 20% castor oil, which obtained a density value of 987 kg/m\({}^{3}\), and this was due to the high density of macadamia nutshell. Moreover, [PERSON] et al. [36] mixed gum Arabic with mahogany leaf particles with a proportion of gum Arabic-adhesive in the mixture  
Figure 7: SEM analysis of particleboard (**a**) T1, (**b**) T2, (**c**) T3, and (**d**) T4.  
ranging between 67% and 78%, and obtained densities ranging between 1188 kg/m\({}^{3}\) and 1678 kg/m\({}^{3}\). The high-density panel could be the high specific gravity of the gum Arabic adhesive reported in that study.  
According to ANSI/A208.1-1999, the particleboard made of macadamia nutshell and gum Arabic can be classified as high-density boards (H) since all treatments were above 800 kg/m\({}^{3}\).  
The moisture content values ranged from 7% for treatment T1 to 13% for treatment T4. The high moisture content observed in the treatment T4 could be explained by the weight of the moisture coming from the gum Arabic adhesive used. The moisture content increased with the increase of the density, and one-way ANOVA analysis indicated that there was a significant difference between the four treatment particleboards at a 5% level of significance (F\({}_{3.8}\) = 58.23; \(p\) < 0.05).  
Test results showed that water absorption values ranged from 8% to 25% and 9% to 39% at 2 and 24 h, respectively. On the other hand, the highest thickness swelling, after 2 h and 24 h of submerging samples in water, was found in treatment T1 (6% and 28%, respectively), while the lowest was found in the treatment T4 (0% and 9%, respectively). One-way ANOVA analysis showed that there was a significant level of difference for the four treatments. The percentage of thickness swelling and water absorption increased with the increase in voids as depicted in the scanning electron microscopic analysis of the four treatment panels. The presence of voids in the treatment T1 and T2 particleboards affected the thickness swelling in the same way as water absorption, as these spaces increased the absorption of water of the boards and caused internal swelling [35]. [PERSON] et al. [36] and [PERSON] [35] reported that the presence of many voids in the boards allowed internal swelling. Moreover, the elevated percentage of water absorption and thickness swelling after 24 h could be explained by the fact that gum Arabic is dissolvable in water and thus, the reaction affected the dimensional stability of the boards.  
Finally, the density value increased while the percentage of water absorption and thickness swelling decreased. The lower the density, the more the material swelled and could absorb a high amount of water in proportion with time. This is in line with the findings by [PERSON] et al. [36] who reported that the swelling rate increased linearly with decreasing particleboard density.  
The results of this investigation showed that the particleboard did not satisfy the recommended maximum requirement value of 8% of thickness swelling after 24 h provided by ANSI/A208.1-1999 for general-purse particleboards, except for treatment T4. The particleboard could not function effectively in particularly humid settings or when it came into contact with water or moisture.