Physical and mechanical properties of Robinia pseudoacacia wood in artificial forests

ObjectiveRobinia pseudoacacia, as an important fast-growing timber tree species in China, is widely used in plantation in northern China. In order to provide a scientific basis for the construction and management of Robinia pseudoacacia plantation and efficient and meticulous utilization of wood, it is very necessary to further study the physical and mechanical properties of Robinia pseudoacacia wood.

MethodIn this paper, 4 different tree-age plantations of Robinia pseudoacacia collected from the coastal forest farm of Dongying, Shandong Province of eastern China were divided into 0.65 m long segments along the tree trunk and numbered in sequence. The physical properties (air-dry density, absolute-dry density and basic density) and mechanical properties (compressive strength parallel to grain, radial compression entire strength perpendicular to grain, the tangential compression entire strength perpendicular to grain, bending strength, bending elastic modulus) and chemical components (cellulose, hemicellulose and lignin) content of wood in different ages and varied heights were measured and analyzed.The microscopic structure of each section of wood was compared and analyzed by scanning electron microscope.

ResultThe results showed that wood air-dry density, absolute-dry density, basic density, compressive strength parallel to grain and compression (entire) strength perpendicular to grain(radial and tangential), bending strength, bending elastic modulus all increased with tree age increasing, and with the increase of trunk height position, the above variables increased first and then decreased. The wood air-dry density was fitted by linear and power functions fitting to the compressive strength, the transverse compressive strength, the bending strength and the bending modulus of elasticity. It was found that the two models can fit the experimental results well, and the fitting R² was 0.865-0.895. The changing rules of cellulose content in chemical components of each wood segment with tree age and trunk height position were similar to those of each mechanical property of wood. In the microstructure of wood, the ratio of duct decreased with the increase of tree age, and showed a rule of decreased first and then increased with the increase of trunk height position.

ConclusionThe results show that the air-dry density, compressive strength parallel to grain, bending strength, bending elastic modulus of 10 years old, 15 years old, 20 years old and 25 years old Robinia pseudoacacia wood were all above intermediate level and these are good furniture and building wood. The difference in varied tree age and varied trunk height position should be taken into full consideration when utilizing wood. As a direct factor influencing the mechanical properties of wood, density can be used to estimate partial mechanical properties of Robinia pseudoacacia wood according to the relevant equations. The cellulose content of Robinia pseudoacacia wood is highly correlated with the macro mechanical properties of wood, while the difference of wood duct occupation ratio reveals the intrinsic reason of wood density change from microscopic structure.