Effects of polyvinyl alcohol on leachability and efficacy of boron wood preservatives against fungal decay and termites attack

In this study, the use of polyvinyl alcohol (PVA) as boron fixative agent was investigated. Two levels of PVA (2.5 and 4%) were evaluated with disodium octaborate tetrahydrate (DOT) at three concentrations (1, 2 and 4% boric acid equivalent (BAE) using a double vacuum impregnation processes on Scots pine sapwood specimens. Leaching was performed according to a laboratory leaching procedure. Boron analysis using atomic absorption spectrometer showed a significant reduction in boron leachability for the samples treated with both concentrations of PVA when compared to the stand-alone boron treatment leading to boron retentions capable to prevent wood biological degradations. Decay resistance of the leached specimens was evaluated using the brown rot fungus Poria placenta. Even if complete protection was not fully achieved, an improvement of decay resistance was observed for the samples treated with DOT in presence of PVA. This leak of efficacy was attributed to a decrease in the biological activity for the complexed boron against fungi. Durability of treated wood against termites attack, evaluated using Reticulitermes santonensis, indicated a significant enhancement for the samples treated in presence of the fixative agent comparatively with the pure boron treatment. (Résumé d'auteur