Preservative Action of Bound Copper and Zinc

Lower retentions of copper and zinc are needed to protect wood from decay when these metals are supplied as sulfates or chlorides than when copper or zinc acetates are used. Binding the copper and zinc ions to the wood structure by treatment with the acetates makes them less available for toxic interactions with the fungi. Southern yellow pine sapwood cubes, 3/4 inch on each side, were impregnated with 2, 1, 0.5, 0.25, and 0.12 percent solutions of copper sulfate and zinc chloride. Control blocks were impregnated with distilled water. After drying and without leaching, the treated blocks and controls were exposed to four species of wood-destroying fungi by standard ASTM method D 1413-56T (Soil block test). For copper and zinc acetate treatments, only one impregnation was made with strong solutions to ensure maximum binding of the cations. A 7 percent copper acetate solution and a 10 percent zinc acetate solution were used. The retentions of salts, the fungi used, and the weight loss on exposure to these fungi for blocks treated with zinc chloride, zinc acetate, copper sulfate, copper acetate, and copper formate are presented in tables.

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