Biological resistance of wood treated with zinc and copper metaborates

Insoluble metaborates were formed by impregnating wood with borax and metallic salts, and the biological resistance of samples treated with metaborates was evaluated. The double-diffusion process was carried out to form metaborate precipitates in sapwood specimens of Japanese cedar ( Cryptomeria japonica ). Water-saturated wood specimens were first impregnated by a saturated borax solution and then diffusion-penetrated with solutions of zinc sulfate or copper sulfate of different concentrations. In laboratory-scale termite tests of wood specimens treated with zinc and copper metaborates at five concentrations from 3% to 20% using a virulent subterranean termite ( Coptotermes formosanus ), metaborate-treated wood showed negligible weight loss, with high termite mortality at the lowest concentration of 3%. An additional termite test for treatments at lower concentrations of 1% and 2% revealed good termite resistance even with small weight gains of 2.3–6.7%. In field termite tests using a tropical dominant termite ( Macrotermes gilvus ) in Serpong, Indonesia, wood specimens of 2 cm (r)×2 cm (t)×10 cm (l) treated with metaborates at 5% and 20% showed little weight loss against termite attack for 2 months or more. In addition, in a decay test using a white-rot fungus ( Trametes versicolor ) and a brown-rot fungus ( Fomitopsis palustris ), metaborate-treated woods showed enhanced decay resistance. This superb enhancement of biological resistance against termite and decay attacks is considered to be attributable to the presence of metaborates containing effective components such as boron, zinc or copper in the cell walls, which were detected by EPMA observations.