Copper based wood preservative - A new approach using fixation with resin acids of rosin
C Roussel, J P Haluk, A Pizzi, M-F Thévenon
Copper soaps with carboxylic acid groups of resin acids of rosin were shown to be potential long-term wood preservatives. The principle involved is the attachment of copper to the network formed by the inorganic part of the preservative (rosin) through the -COOH groups. The mechanisms of fixation have been studied, and it has been shown that this association could be obtained : (1) by forming the salt (a mix of rosin and NaOH where CuSO4 is added), and then impregnate (with a vacuum/pressure system) the wood with this product dissolved in ethanol, or (2) by using a double impregnation system with water solutions of the mix rosin-NaOH first, and a CuSO4 solution second, the salt being then formed within the timber. The biocidal mechanisms are based on the realease of Cu2+ by hydrolysis of the -(COO - )2Cu2+ when very humid conditions occur, this being reversible when wood moisture content is decreasing. Treated wood mini-blocks have shown good performances when leached, and biological tests assessed the good durability of such treated and leached timber.