Tannin-boron preservatives for wood buildings: mechanical and fire properties

The remarkable biological properties of tannin-boron wood preservatives for outdoor applications have been investigated recently (Thevenon et al. in Eur. J. Wood Prod. 67:89, 2009). In the present paper mechanical and fire-proofing attributes of these formulations are determined. Mechanical properties of Scots pine and beech specimens treated with tannin-based formulations were examined in compression and bending strength tests and surface hardness was determined. The tannin-hexamine formulations reticulated into the wood structure improve the strength of the treated specimens. The treated samples which underwent compression, bending, hardness and gluing tests showed improvements of on average 20%. Fire tests have been monitored regarding short and long flame exposure time. Short tests such as ignition, flame and ember time have allowed the ignition of the fire to be simulated, while the weight loss tests have provided a good overview of the behavior of the specimens during prolonged fire. A positive effect on fire-resistance is shown when wood is treated with tannin formulations. The fire-proofing properties of the resin have been upgraded adding boron and phosphorus. The ember time of the pieces treated using this method can be reduced by up to ten times.