An investigation of antifungal properties of tannins as a potential wood preservative

The aim of this study was to improve biological resistance of Scots pine wood against wood destroying fungi with tannins. In the first part of the study, wood samples were impregnated with 5 and 10% concentrations of gallnut powders, sumac, quebracho, mimosa and valex tannins, and then were exposed to 7 different microorganisms belong to family of Basidiomycetes and Ascomycetes- Fungi imperfecti. In the first part, wood samples impregnated with tannin solutions exhibited high biological resistance against brown rot fungi however they had a poor protection against T. versicolor attacks. Tannins did not have a sufficient protection against microorganisms belong to Ascomycetes-Fungi imperfecti. Quebracho tannin was determined as the best tannin type for protection. Tannins leached from wood during the leaching test. In the second part of the study, tannin fixation into wood was aimed. For this purpose, samples were impregnated with 0.5, 1, 2, 3 and 5% concentrations of quebracho tannin and then were impregnated with 0.25, 0.5, 1, 1.5 and 2.5% copper II sulfate, zinc chloride, nano ZnO and CeO2. Leached and unleached samples exposed to brown and white rot fungi attacks, and fixation of tannin+chemicals were evaluated. The results showed that, combination of tannin with nano ZnO and CeO2 had a synergistic efficieny against T. versicolor attacks while tannin and copper II sulfate and nano CeO2 combinations were found to better efficieny against C. puteana attacks. In the tannin and metal combinations, the required chemical concentrations for a proper protection were reduced and good decay resistance was ensured.