A New Boron Fixation Mechanism for Environment Friendly Wood Preservatives

A boron fixation mechanism based on a novel reaction in which boric acid induces autocondensation of flavonoid tannins is described. The boric acid is partly fixed to the network by the autocondensed tannin in the wood but conserves sufficient mobilitiy to mantain its preservative action. The system is based on slowing down the potential leaching of boron from the wood without completely stopping its mobility. Apparent reaction rate constants with very simple model compounds are presented as well as results of accelerated termite field tests. The results indicate that this low toxicity, environment friendly treatment using a natural material increases permanence of boron in the wood with consequent preservative durability between three and six times. It does not appear suited then, at the low retentions used experimentally, for ground contact applications but only for aerial, non-ground contact ones. A double treatment procedure was used at laboratory level in order to confirm the mechanism action, but both treatments were water-borne.