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Wood protection using tannin-boron associations

Tondi G., Wieland S., Wimmer T., Petutschnigg A., Leménager N., Pizzi A., Thévenon M.F.. 2012. In : eds. Stefanie Wieland, Thomas Schnabel. COST Action FP1006 Workshop Basics for Chemistry of Wood Surface Modification, Programme and book of abstracts, April 25-27, 2012, Kuch, Salzburg, Austria. Salzburg : Salzburg University of Applied Sciences, p. 81-82. COST Action FP1006 Workshop Basics for Chemistry of Wood Surface Modification, Salzburg (Autriche).

Wood, a renewable resource used for many applications, needs to be preserved against biological degradation when its natural durability can not provide sufficient protection for an expected service-life in a use-class. Amongst natural compounds, polyflavonoids (condensed tannins) are used by plants as defense against biological attack by insects, fungi and bacteria [1]. Tannins can be easily complexed to create networks fixing other molecules acting as active ingredients. These associations have already been experienced to protect wood [2, 3]. In this study, the concept is to complex boron (in the form of boric acid) with tannins and to waterproof this association by using a hardener (such as hexamine). Tannins and hexamine are already used as zero formaldehyde emission adhesives [4]. This system would allow to fix boron at much lower levels than those authorize by the EC directive 2008/58/EC in order to carry on using this biocide with many advantages [5]. Many combinations of tannins (different origins, quantities), boric acid, hexamine and other additives (phosphoric compounds, ...) have been considered and used to treat Scot pine sapwood and beech. The treated wood samples, onced dried at 103°C, were conditioned prior to leaching (EN 1250-1 or 5 days leaching). The leaching waters were analysed for their boron content showing interesting boron retention. The wood blocks were tested for resistance towards Basidiomycete fungi (brown and white rots, temperate and tropical strains, according to the guidelines of EN113), as well as termites (according to EN117) [6, 7]. Except for a few mixes, the treated and laeched wood blocks were protected against decay. The results of termite tests also showed a good protection compared to the controls. The results of the most interesting formulations will be presented with emphazise on the problems encountered when testing timber protected with a "non conventional" product/process. The treated wood also presented different surface properties, and interesting behaviour in terms of fire resistance [8].

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