Protein borates as non toxic wood preservatives

Protein borates used as wood preservatives were shown to have effectiveness against wood decay, and, to also be a good method to reduce boron leachability. Boric acid can be partially fixed to timber by formation of an association with different kind of proteins (egg albumin, gelatin, casein, soya proteins) which are insolubilized by heat-induced coagulation. Accelerated biological tests using Basidiomycetes have shown that timber treated with protein borates has durability performances comparable to those obtained with CCA, even when leached. Among the protein borates, egg albumin can particularly be classified as non-toxic, long-term, wide-spectrum wood preservative. Chemical investigations on fixation mechanisms of boric acid by egg albumin indicated that both acid-base salt formation occurs, as well as the formation of boric acid-protein complexes, depending on the boric acid/protein ratio. These mechanisms leaving at all times small amount of boron free to exercice its antifungal activities, reduce drastically its tendency to leach. Boric acid leaching as a function of time appears to tend to an equilibrium value which depends on the type of protein used, and differs in the case of treated timber from what is obtained by just leaching the protein borate coagulate alone. (Résumé d'auteur