The efficacy of Mimosa tannin, chemically modified tannin, and tannin-copper complexes as wood preservatives was studied. When the tannin-ammonia-CuCl2 solutions were impregnated into wood specimens in a one-step procedure, a large quantity of the tannin-copper complex was fixed in the specimens. Little of the complex was leached from specimens by a weathering treatment, and these specimens showed satisfactory decay resistance in a basidiomycete laboratory test according to the Japanese Industrial Standard (JIS) K 1571-1998. Only the tannin-treated wood had a retention of agent after treatment, in increasing order from untreated tannin (MT), resorcinolated tannin (RMT) and catecholated tannin (CMT). When RMT or CMT was mixed with ammonia¡copper, the wood retained twice as much of these solutions as the MT-ammonia-copper solution. The solutions penetrated 2~13mm from the tangential sections of the logs. Presumably, chemical modification increased the degree of retention by altering the structure of the tannin and increasing its hydrophilic properties. The degree of retention of RMT-NH3-Cu and CMT-NH3-Cu in logs with cross-sections ranged from 268 kg/m3 to 326 kg/m3. Wood decay by F. palustris was markedly suppressed by processing wood with agents made by mixing chemically modified tannins with ammonia and cupric chloride. When wood powder was treated with these agents, mycelial growth and generated protein increased to some extent. The preservative effects of the chemically modified tannins (RMT and CMT) or compound agents composed of the tannins and ammonia¡copper were considered to be due to inhibition of the activities of mannase and Cx-cellulase. In the culture medium which treated wood powder was put in with these agents, drop of pH by oxalic acid, which Fomitopsis palustris produces, is not generated. The potency of the effect was thought to be due to chelation of copper, an essential trace element for wood decay by F. palustris, by the tannin, and/or neutralization or suppression of oxalic acid production by ammonia-copper. Also, these active ingredients hindered eating-damage of wood by the termites. However, the mortality of the termites during the eating-damage test (over 21d) did not reach 100% for all active ingredients. The fact that living termites were still present suggests that tannin-ammonia-copper is not perfect for destroying termites.

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