Thermal modification is an attractive alternative to improve the decay durability and dimensional stability of wood. However, thermally modified wood is generally not resistant to termite attacks, limiting the field of application of such materials. One way to overcome this drawback is to combine thermal modification treatment with an additional treatment. One such treatment is the impregnation of a boron derivative associated with appropriate vinylic monomers, which takes advantage of the thermal treatment to polymerise these monomers for boron fixation. Using this strategy, we recently showed that an impregnation of borax (2 or 4% boric acid equivalent) dissolved in a 10% aqueous solution of polyglycerolmethacrylate followed by thermal treatment under nitrogen at 220°C protects wood from both termite and decay degradations, even after leaching. Additionally, wood samples treated with a 10% polyglycerolmethacrylate aqueous solution and subjected to thermal treatment at 220°C presented improved resistance to termites while avoiding boron utilization. Based on these results, we investigate the effect of impregnation with two types of vinylic monomers, which are already used in the presence of boron, followed by thermal treatments at different temperatures. We evaluate termite and decay durability of wood to evaluate if thermal modification associated with light chemical modification could be a solution for utilization of thermally modified materials in termite-infested areas. (Résumé d'auteur

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Environmental pressures in France and in most European countries during the last decade have led to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment is one of the most investigated alternative methods. Important chemical modifications resulting from thermo-degradation reactions confer new properties to wood, like increased decay resistance or higher dimensional stability, while mechanical properties like tensile strength decrease after treatment. However, the improved durability of heat treated wood is not sufficient to allow its utilization in ground contact, where it is subjected to insect and fungi attacks. Impregnation with borax before thermal treatment could be an interesting method to improve the properties of thermally modified wood. Boron is a relatively harmless biocide that improves resistance to fungi and insects like termites. Additionally, borax can also improve wood fire resistance due to its fire retardant effect. To reduce boron leachability, two additives previously developed in the laboratory corresponding to water soluble polymerizable polyglycerol derivatives were added to the borax solution, taking advantage of thermal treatment to fix the latter through polymerization within the wood structure limiting boron leachability. (Résumé d'auteur

Wood-plastic composites (WPC) have many applications as structural and non-structural material. As their outdoor application becomes more widespread, their resistance against weathering, particularly ultraviolet light and biodegradation becomes of more concern. In the present study, natural fiber composites (NFPC) made of bagasse and high density polyethylene, with and without pigments, were prepared by extrusion and subjected to accelerated weathering for 1440 h; then weathered and un-weathered samples were exposed to fungal and termite resistance tests. The chemical and surface qualities of samples were studied by ATR-FTIR spectroscopy, colorimetry, contact angle, and roughness tests before and after weathering. Using bagasse as filler does reduce the discoloration of weathered samples. Adding pigments may reduce the effect of weathering on lignin degradation, although it favors polymer oxidation, but it increases the weight loss caused by fungi. Despite the high resistance of samples against biological attack, weathering triggers attack by termites and fungi on the surface and causes surface quality loss.

Wood preservatives based on protein borates and in particular albumin borate greatly retarded the leaching of boron from treated timber. Accelerated biological tests indicated that boric acid partially fixed to timber by formation of a salt with albumin and other proteins which are then insolubilised by heat-induced coagulation can yield durability comparable to that obtained with CCA wood preservatives. The results of the biological tests show that protein borates, and particularly albumin borate, can be classified as long-term, wide-spectrum, ground-contact, heavy-duty wood preservatives, and are only composed of boric acid, a non-toxic to mammals biocide and of a non-toxic, natural, sometimes waste material, namely a protein. Investigation of the chemical mechanisms of boric acid fixation by the protein indicated that both acid-base salt formation occurs, as well as the further formation at increasing boric acid proportions of additional boric acid/protein complexes. The mechanism is hence only one of partially reversible rather than totally irreversible fixation of boron, leaving at all times small amounts of boron free to exercise its antifungal activity, but drastically diminishing its tendency to leach and greatly retarding its leaching. Boric acid leaching as a function of exposure time appears to tend to an equilibrium value which is different for each type of protein used and differs in the case of treated timber from that obtained by just leaching of the protein borate coagulum.