Tannin-boron wood preservatives

Tannin-boron wood preservatives are alternative products to replace water-borne formulations based on copper. Interesting results in protection against fungus (pycnoporus sanguineus) were achieved with formulations based of 20% tannin solutions containing boric acid (Thevenon et al. 2009). In this paper two upgrades are introduced: extension of preservation properties to softwood species (scots pine) and analysis of the side-properties achieved after treatment. A detailed study on tannin penetration in beech and scots pine is presented. Microscope analysis demonstrates that impregnation in scots pine have two preferential directions: Longitudinal through tracheids and radial through parenchyma rays, while in beech the liquid penetrates the wood cell mainly longitudinally through large and easy accessible vessels. Commercialization of exterior-door wood preservative will be also dependent on the side-properties derived from the treatment. For this reason, properties such as mechanical resistance and behavior against fire have been investigated. The mechanical tests have shown a strong increasing of compression resistance and surface hardness for beech and scots pine samples. The tests against fire have been monitored considering ignition, flame and ember time. A broad positive effect on fire-repellence is shown when wood is treated with tannin-boron formulations. (Résumé d'auteur