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As a substitute for high-cost copper azole (CuAz) and alkaline copper quaternary (ACQ) wood preservatives, alternative wood preservatives were formulated with okara, which is an organic waste from the production of tofu, and copper chloride and/or borax. Each preservative was used in treatment of wood blocks in a reduced-pressure method to measure its treatability. The treated wood blocks were placed in hot water for 3 days to examine the stability of the preservatives against hot-water leaching. The preservatives successfully penetrated into wood blocks, probably due to the use of ammonium hydroxide as a dissociating agent. However, the stability of okara-based preservatives dropped as the concentration of acid in the solutions used for hydrolysis of okara increased. The treatability and leachability of the preservatives were not affected by hydrolysis temperature but were negatively affected by the addition of borax. Leached wood blocks treated with okara-based preservatives and exposed to decay fungi Gloeophyllum trabeum and Postia placenta over 12 weeks showed good decay resistance. Okara-based wood preservatives can protect wood against fungal attack as effectively as CuAz, and have potential for use as environmentally friendly wood preservatives.

Larch (LAR) and yellow poplar (YP) cubes were torrefied at 180, 220, and 260 °C for 50 min to determine the alterations in their structural and hydrophobic properties. Through microscopic observations, several cracks and crevices were found on the radial-and tangential-sectioned areas of the 260 °C-torrefied YP cubes. On the tangential-sectioned areas, horizontal resin canal for LAR and ray cells for YP were darker than vertical cells. Moisture absorptivity (MA) measured for investigating the hydrophobicity of the torrefied LAR and YP cubes decreased with the increase of torrefaction temperature. However, no obvious differences were observed between the colors of the surface and internal parts or between the internal parts of the cubes visually at each torrefaction temperature. In addition, MA of the LAR and YP cubes was not significantly influenced by the depth of the cubes. Accordingly, it can be concluded that the carbonization level of the LAR or YP cubes is affected more by torrefaction temperature than by the cube depth. On the other hand, pelletization of the torrefied LAR and YP cubes using a piston-type single pelletizer was conducted to investigate the durability of torrefied pellets. Results showed that pellets made with torrefied YP cubes were more durable than those with torrefied LAR cubes at each torrefaction temperature. Durability of the torrefied LAR and YP pellets decreased with the increase of torrefaction temperature. Therefore, torrefaction temperature of 260 °C and above might be not an effective treatment to produce strong torrefied pellets.