Evaluation of the Mechanical Properties, Microstructure and Biological Resistance of Six Species of Wood Treated with Tannin-Boron Preservative

Tannin-boron (TB) treatment is an effective method for enhancing the biological resistance of some types of wood, although knowledge regarding its efficacy as a preservative in a wider range of wood is limited. In this study, we investigated the effects of TB treatment on the mechanical and microscopic properties, and on biological resistance of six types of wood (Pinus massoniana Lamb., Cunninghamia lanceolata (Lamb.) Hook, Pseudotsuga menziesii (Mirb.) Franco, Intsia bijuga (Colebr.) Kuntze, Tectona grandis L. f., and Quercus mongolica Fisch. ex Ledeb.). The results showed that the six types of wood exhibited different boron retention after leaching, with the highest retention rate, 21.85%, observed in P. massoniana. The TB treatment did not significantly alter the original density and compressive strength of the wood, except in the case of I. bijuga, where the compressive strength significantly decreased after treatment. Scanning electron microscopy revealed that TB preservative is attached around the tracheids of softwood, or deposited within the vessels of hardwood. No-choice feeding tests showed that the TB-treated wood exhibited high resistance to Coptotermes formosanus with a maximum weight loss of 2.5%. TB treatment significantly improved the resistance of P. massoniana, C. lanceolata, P. menziesii, and T. grandis to Trametes hirsuta. These results demonstrate the potential usefulness of TB preservatives in different wood types.