Some wood anatomical features of Acacia mangium Willd. affect the drying process
Keywords:
Anatomy, drying defect, drying rate, moisture movement, porositAbstract
This study investigated the microscopic structure and porosity of 9-year-old Acacia mangium Willd., harvested in Ngoc Thanh commune, Phuc Yen city, Vinh Phuc province, as a fundamental information for predicting the moisture movement and phenomena during drying. Descriptions were made by observing a combination of ESEM (environmental scanning electron microscope) scans and OM (optical microscope) images taken in cross, radial and tangential sections. The results showed that the vessel diffuse pattern and the pit membrane on the cells wall with no central torus, always presented openings, eliminating the difference between the permeability of the early and late wood and that of wood components in the radial direction. The vessels were arranged in a solitary pattern or in multiples in various formations (2-3 porous). This was an ideal condition for the moisture movement in the longitudinal direction. The diameter of the vessels in the tangential direction was 88 - 200 µm, with a quantity of 5 - 8 vessels/mm². The simple and low bordered perforation plate allows moisture to be transported in the longitudinal direction easily. The ratio of fibre lumen diameter over cell wall thickness was 4.09. This was the reason for the high collapse degrade of A. mangium Willd. during drying. The structures of axial parenchyma cells and rays were identified. They did not too affect moisture movement, but they were used for explaining drying defects. The red-brown accumulations, which was seen in vessels and rays and the prismatic crystals, which was located in axial parenchyma cells obstruct the moisture flow. The calculation of the fibre and vessel porosity, which was done by the determination of the ratio of total pores area over image area using ImageJ software for the prediction of the drying rate. The fibre, vessel and total porosity was 37.06 ± 3.96%, 16.03 ± 1.23% and 47.15% respectively. This was a very important characteristic that affects the drying rate
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