Biological resistance of FFA (furfuryl alcohol)-treated wood was investigated in relation to the rise of ASE (anti-swelling efficiency) resulting from the treatment. Sapwood blocks of Japanese red pine, cedar and beech were vacuum-impregnated with various concentrations of aqueous FFA solutions to get the target levels of% (w/w) RL (resin loading). Air-dried blocks were kept in an oven at 120°C for 8 hours to insure the resin formation submerged in water for 1 week to leach away the unpolymerized portion, re-dried, and exposed to decay fungi and termites. The treatment was more effective for pine and cedar than for beech to enhance their decay resistance. As in cases of chemical modification, the treatment was more effective against white-rot fungus Coriolus versicolor than brown-rot Tyromyces palustris. The required RL to reduce the decay by Coriolus versicolor to less than 3% weight loss was ca. 20% for both softwoods but it was ca. 30% for Tyromyces palustris. FFA-treated woods were less attacked by a destructive subterranean termites Coptotermes formosanus and caused their higher mortality with the increase of RL. The pretreatment of boric-acid impregnation yielded the higher ASE and biological resistance at the lower RL than those of sole FFA-treatment. Decay by Coriolus versicolor virtually eliminated even at 0.5% RL for the treated pine and cedar subjected to the boric acid pretreatment.

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