Decay and termite resistance of pine blocks impregnated with different additives and subjected to heat treatment

Environmental pressures in France and in most European countries during the last decade have considerably changed the practises for wood protection. In this context, legislation and regulations, among which the Biocidal Products Directive (BPD) and Biocidal Products Regulations (BPR), are more and more constraining leading to the development of more environmentally acceptable preservation formulations and to an increasing interest in non-biocidal alternatives like thermal or chemical modifications. Wood heat treatment has been one of the most investigated alternative methods during the last years. However, even if some of the wood properties, like its decay resistance or and dimensional stability, are improved, the overall durability of the material is not sufficient to envisage use class 3 and 4 applications, where the wood is in direct contact with soil and termites. Impregnation of borax associated to polyglycerolmethacrylate (PGMA) before thermal treatment could be an attractive alternative to improve the performance of thermally modified wood in ground contact and especially its resistance to termites taking advantage of thermal treatment to initiate polymerization of PGMA within the wood structure to limit boron mobility. Thermo-modification with or without combination of boron impregnation and PGMA improved the durability of all wood samples. Thermal treatment alone or after boron impregnation and leaching was unable to effectively protect wood blocks against termites after leaching, while bocks treated with boron and PGMA were shown to be fully resistant to termites. More surprisingly, association of thermal treatment and PGMA impregnation without boron impregnation also produced protection against termite attack. Such treatments may be valuable alternatives to extend the scope of utilization of thermally modified wood in outdoor conditions.