Potentialities of protein borates as low-toxic, long-term wood preservatives - Preliminary trials
M-F Thévenon, A Pizzi, J P Haluk
Boron compounds are efficient wood preservatives, as well as safe for the mammals and environmentally acceptable. Their natural solubility allows them to treat almost any wood species, but is also the cause of their high depletion from treated timber in outside exposure. In order to reduce this leachability, potentialities of proteinic polymer networks retaining boron within the wood have been investigated. Several mixtures of boric acid and proteins (including ovalbumin, collagen, casein, soya flour) have been used to treat pine sapwood miniblocks. The insoluble networks were obtained by protein gelation or coagulation, induced by a physical and/or a chemical factor. These systems appeared to retard boron leaching, the decrease of the leachability rate depending on the protein and the denaturing agent involved in the network creation. The best results have generally been observed for the irreversible heat-induced protein gels. These associations are also able to conserve some boron mobility and activity. Accelerated biological tests of leached wood samples showed good durability performances against Basidiomycetes. The use of protein borates seems to be an interesting basis for low-toxic wood preservatives. Furthermore, in some cases, proteins could add their anti-nutritional factors to boron efficacy to enhance wood protection.