On the other hand, increasing the ratios of either KS or KC particles
in the middle layer of the samples decreased their stabilities.
Nonetheless, these values were significantly higher than those of
Type 7 panels. This can be ascribed to the presence of kenaf bast
particles in the Type 7 panels. In a previous study [22], kenaf bast
was reported to be having low wettability. This could have contributed
to the low water absorption of the Type 7 panels. However,
swelling and water absorption of the sample were relatively high
in Type 8 panels, which can be due to the massive amount of KC
employed in manufacturing the board owing to the low density
of KC. Accordingly, when the samples were submerged in water,
low-density wood and a high absorbant material such as KC might
have increased the TS and WU of the boards since kenaf required
large volume of particles to equate the mass and achieve the targeted
board density [21,23]. Furthermore, once immersed in water,
the UF resin, which is designed for interior applications, is not
durable under outdoor exposure conditions.
In this study, some mechanical and physical performance characteristics
of three-layer, rubberwood–kenaf particleboards were evaluated. The MOE of Type 1 panels was 56% and 79% higher than
those of the single-layer panels made from kenaf stem and core
particles, respectively. The three-layer particleboards manifested
a significant increment in elasticity. Increasing the ratios of RW
particles in the surface layer increased the strengths of the resultant
panels. Based on these findings, it is concluded that the
three-layer rubberwood–kenaf particleboards comprising up to
30% of KS with 10% UF resin are the ideal panels.