Environmental pressures appeared in most European countries during the last decade has lead to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment has been one of the most investigated alternative methods during the last years. Treated at temperatures ranging between 180 and 220°C, wood components undergo more or less important chemical modifications conferring to the material new properties like increased decay resistance or higher dimensional stability. However, even if some of the wood properties are improved, the overall durability of the material is not sufficient to envisage use class 4 applications, where the wood is in direct contact with soil. Impregnation of borax before thermal treatment could be an attractive way to improve properties of thermally modified wood. Indeed, boron is known as biocide allowing not only improving decay durability but also resistance to insects like termites. The main drawback of boron is its poor retention in wood due to its high leachability with water. To reduce boron leachability, polyglycerol methacrylate was added to the borax solution taking advantage of thermal treatment to initiate polymerization within the wood structure in order to limit boron mobility. Samples were the subjected to leaching before evaluation of their durability using different white rot and brown rot fungi. Results indicated a significant improvement of wood durability of treated samples even after leaching. Such treatments may be valuable alternative to extend the scope of utilization of thermally modified wood in outdoor conditions.

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