Nirundorn Matan and Buhnnum Kyokong

pp. 327 - 340

Abstract

Moisture content of rubberwood is an important factor influencing its physical and mechanical
behaviours. This research aimed at quantifying effect of moisture content on physical and mechanical
properties of juvenile rubberwood core. The specimens at various moisture contents were tested in compression and shear parallel to grain. Information was gathered to determine shrinkage, density and specific
gravity of specimens. The equilibrium moisture content determined from desorption experiment, was well
described by the Hailwood-Horrobin solution theory. Moisture content of 23±4% best represented the value
of apparent fiber saturation point, Mp, determined from physical and mechanical properties data. Above
Mp, values of all physical and mechanical properties examined were fairly constant. Maximum volumetric
shrinkage from moisture content above Mp to an oven-dry condition was 8.2±1.8%. Specific gravity and
density were 0.55±0.03 and 614±30 kg/m³ at 12% moisture content. Below Mp, ultimate compressive stress
(UCS) parallel to grain, ultimate shear stress parallel to grain, modulus of elasticity (MOE) for compression
parallel to grain, and shear modulus parallel to grain increased exponentially with decreasing moisture
content. Shear strain at fracture and work to fracture of shear parallel to grain were found to increase as moisture content decreased below Mp and attained the maximum values at 20% and 12% moisture content,
respectively. The values decreased with further lowering of the level of moisture content. Ultimate compressive
stress (UCS) parallel to grain was closely correlated with specific gravity and was more sensitive to changes
in moisture content at higher specific gravity level.