Albumin borate: A new non-toxic, wide-spectrum, long-term wood preservative
M-F Thévenon, A Pizzi, J-P Haluk
Boron, widely recognized for its broad range of activity towards both fungi and insects and for its low mammalian toxicity, can not provide long term protection to treated timber due to its high leachability.
Boron, in the form of boric acid, can be partially fixed to timber by the formation of an association with egg albumin, which is insolubilized by heat-induced coagulation. 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-albumin complexes, depending on the boric acid/protein ratio. In treated timber, a chance in protein conformation in presence of boric acid, has been shown by scanning electron microscopy.
These mechanisms, partly reversible, while greatly retarding its leaching, leave small amounts of boron free to exercice its activity when needed. Boron leaching as a function of time, appears to tend to an equilibrium value, which one differs in the case of an albumin coagulum alone from what is obtained by leaching treated wood samples. Accelerated biolocical tests using such treated timber have shown that albumin borate used as wood preservative has effectiveness against wood decay, and have durability performances comparable to those obtained with CCA.