Outdoor timbers treated with albumin borates : an environmentally friendly way of preserving wood

Boron compounds are efficient wood preservatives against fungi and insects, and are widely recognized to be safe towards both environment and mammals. Their natural water solubility allows them to easily treat timber. On the other hand, this property makes borates readily leachable from treated timber. Thus, borates provide only short term protection in outside exposure. Wood preservatives based on albumin borates have been shown to greatly reduce boron leachability, even when the treated timber is in ground contact under natural exposure. Aqueous mixtures of boric acid and albumin (albumin 1% m/m and boric acid 3% or 5% m/m) were used to treat pine small poles (1 m length, 20 cm diameter). The treatments were performed with a vacuum-pressure pilot plant system. Further to this impregnation, the poles were dried at 90°C, 70% RH in a convective wood dryer. The aim of this drying operation was to coagulate the protein, creating thus an insoluble polymer network able to retain the boron within the wood. Half of these treated poles were buried in a field test site. Retentions and distributions of boric acid and albumin in the poles were determined after the treatment and after 3 years of field testing. Observations of the degree of biological attack revealed that poles treated in this manner with only 3% boric acid were moderately durable, and the poles treated with 5% boric acid remained durable, even in ground contact. (Texte intégral