Changes of Moisture Content and Chemical Composition of Wood Chips during the Steaming Process in the Production of Medium Density Fiberboard

Abstract

Changes of moisture content and chemical composition of wood were evaluated to determine the optimum conditions for the steaming process in the production of medium density fiberboard. Wood chips with specific moisture contents (10, 30, 60 and 90%) were cooked in a small pressure vessel under a pressure of 0.70 MPa for 1 to 18 minutes. Species used were Acacia mangium (Acacia mangium Willd.) and sugi (Japanese cedar, Cryptomeria japonica D.Don). Changes of moisture content (MC) and chemical composition of the chips were evaluated after the cooking process. The specimens with lower initial MC (10, 30 and 60%) absorbed water during the process. Thickness of the chips did not affect the water absorption per unit area; therefore it is presumed that water diffusion occurred evenly through cell wall, pit membrane and lumen. On the other hand, the specimens with higher initial MC (90%) temporarily released a small amount of water at the beginning of the process, and then absorbed water again to the initial MC. For the chemical composition of Acacia, holocellulose decreased by 10% in 12 minutes of steaming regardless of the initial MC of the specimens. This was attributed to degradation of the hemicellulose.