Chemically Modified Tannin and Tannin-Copper Complexes as Wood Preservatives

The efficacy of mimosa tannin, chemically modified tannin, and tannin-copper complexes as wood preservatives was studied. When the tannin-CuCl 2 -ammonia 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) A 9302-1976. However, the treatment of wood specimens with the copper-ammonia complex was also effective in preventing decay, and therefore it could not be said categorically that the tannin contributed significantly to the biocidal effects of tannin-copper-ammonia complexes. When aqueous solutions of mimosa and chemically modified tannins were impregnated into samples of wood, in comparison with unmodified tannin, the resorcinolated and catecholated tannins were more effective in preventing fungal decay. Chemically modified tannins were also effective in inhibiting the growth of a white rot fungus (C. versicolor) and a brown rot fungus (T. palustris) in a static liquid medium. The growth of T. palustris was also inhibited by the resorcinolated and catecholated tannins from which the low molecular weight component were removed by dialysis. Since the weight loss of the wood, which was impregnated with the unmodified tannin and had not undergone the weathering test, during the decay test by C. versicolor was low, it appears that the unmodified tannin had unsatisfactory antidecay properties. However, in the decay test in which T. palustris was used, the antidecay properties of the unmodified tannin were also inadequate. When the unmodified tannin was added to the liquid medium and then the fungi were incubated in the same medium, the growth of C. versicolor was inhibited, but the growth of T. palustris increased by a 1% (w/w) concentration of tannin in the medium.