Preservative properties of vapor-boron-treated wood and wood-based composites

The treatability of wood (sapwood of Cryptomeria japonica D. Don) and wood- based composites (particleboard, waferboard, medium-density fiberboard, ply wood) with vapor-boron was good, and the treated materials proved to be res istant to decay fungi and subterranean termites in laboratory bioassays. No difference in effectiveness was noted between vapor-boron and liquid-boron treatment of wood. Toxic threshold values determined for solid wood were 0 %-0.24-%, 0.26%-0.51%, and 0.26%-0.51% BAE (boric acid equivalent), respect ively, against the white-rot fungus Trametes versicolor (L.: Fr.) Pilat, th e brown-rot fungus Fomitopsis palustris (Berk. et Curt.), and the subterran ean termite Coptotermes formosanus Shiraki, A concentration of less than 1% BAE seemed sufficient to control biological attacks on composites, althoug h the toxic limits could not be determined more accurately because of the t ested range of boron retention. High boron retention was needed to meet the performance requirements for slow-burning materials when a fire-retardant agent was not incorporated into the glue line.