Synthesis of boric acid ammonium oleate salt for wood preservation : leachability and termite resistance test [Preprint]

A new chemical compound coupling boric acid and oleic acid through a joint of ammonium salt has been produced and its synthesis followed and validated by Fourier Transformed Infra Red (FTIR). This compound named ammonium borate oleate (BAO) combining biocidal properties of boron and water repellence of fatty acids has then been studied as a wood preservative. Synthesis of BAO involved different molar rates of oleic acid to determine the best formulation regarding boron retention and resistance to termites. Formulations including four moles of oleic acid for one of boric acid and one of ammonia (1:1:4) have shown the best efficiency compared to formulations 1:1:1, 1:1:2 and 1:1:3 with about 52% of boron remaining after weathering when other formulations retained respectively 10%, 29% and 46% of boron in the case of an impregnation of Japanese cedar sapwood specimens. Seven solutions of 1:1:4 BAO in ethanol of different concentrations were then produced and impregnated sapwood blocks of C. japonica and F. crenata exposed subterranean termites Coptotermes formosanus. Toxicity threshold around 2.0 Kg/m3 BAE for F. crenata and 2.4 Kg/m3 BAE for C. japonica are a bit lower than toxicity thresholds found in previous studies from 2.0 to 4.5 Kg/m3 BAE indicating that boron is available despite its combination with fatty acids. Extremely low mass losses indicate a positive effect of this combination, hydrophobic effect of oil reduces termite attack and boron leaching when boron provides a biocidal protection. Termite mortality rates recorded along the three weeks of exposure precised the action mechanism of BAO as an intermediate between biocidal boric acid and non toxic fatty acid. Termite mortality rates increase with BAO concentration but an inflexion occurs for highest concentrations due to high oil content. (Résumé d'auteur