Durability of tannin-boron treated timber

High performance tannin-boron wood preservatives were investigated for their resistance against outdoor agents. In this work we focused on the analysis of the causes that affect the durability of the tannin-hexamine treated samples. In particular, dimensional stability, resistance to leaching and to biological agents were investigated. Therefore, the combined effect of these deterioration agents was evaluated by subjecting the treated samples to simulated and natural weathering as well as to ground contact tests. The study of the appearance and of the color components (L*, a* and b*) according to CIELAB space of the exposed samples was monitored to assess the efficacy of the tannin-boron formulations for outdoor applications. Significant resistance against the action of water and insects has been demonstrated in specific tests. Conversely the continuous stress due to artificial and natural weathering deteriorates the color and the visible features of the treated specimens. The combined effect of moisture modifications, solar exposition and leaching cycles damages the structure of the tannin-based polymeric network and subsequently it negatively affects its preservation properties.