Effect of mechanical restraint on drying defects reduction in heat-treated okan wood

Abstract

Mechanical restraint through the use of clamps was applied as an attempt to prevent drying defects during the heat treatment of high-density wood. Boards of okan (Cylicodiscus gabunensis (Taub.) Harms) with the initial moisture content of 8.99% and 9.68% for sapwood and heartwood, respectively, were prepared. The boards were heat-treated under an oxygen atmosphere at the peak temperatures of 160 °C, 180 °C, 200 °C, and 220 °C with a residence time of 2 h. The occurrence of drying defects as checks (i.e., surface and end checks) and warps (i.e., bow, cup, and twist) were evaluated. Heat treatment stimulated the occurrence of drying defects in okan wood. The results revealed that the surface checks, end checks, and twists increased linearly with increased temperature. The occurrence of warps, such as bow and cup, after heat treatment was relatively low. Heartwood showed a higher degree of drying defects compared to the sapwood. Application of mechanical restraint by clamping efficiently decreased the occurrence of drying defects of okan wood, particularly surface checks, end checks, and twists.

Effect of a Combination of Moderate-Temperature Heat Treatment and Subsequent Wax Impregnation on Wood Hygroscopicity, Dimensional Stability, and Mechanical Properties

“…Chemical modification can obtain good results in dimensional stability and hydrophobicity; however, it can be harmful to people and the environment [17]. Above all, HT is an eco-friendly and effective approach to increase durability and dimensional stability [18,19] and to reduce wood wettability [20]. However, its disadvantages are obvious in effects such as color change, lowered of mechanical strength, and higher energy consumption [12,21].…”