Comparison of different treatments based on glycerol or polyglycerol additives to improve properties of thermally modified wood

Impregnation of European beech (Fagus sylvatica) with 10% w/w aqueous solution of different additives made from the reaction of glycerol or polyglycerol with glycidyl methacrylate or maleic anhydride followed by thermal modification at 150, 200 or 220 °C under inert conditions was investigated to evaluate potential synergies between chemical and thermal treatments. Treated and untreated wood were analysed to evaluate mass changes and bulking values after treatments, resistance of treatment to leaching, wettability, anti-swelling efficiency, modulus of elasticity (MOE), modulus of rupture (MOR), decay resistance against Coriolus versicolor and termite resistance against Reticulitermes flavipes. Results revealed that synergic effects between a combination of light chemical modification and thermal treatments can be observed at higher temperature treatments (200 and 220 °C), improving wood dimensional stability (approximately 80%), decay, and termite resistance properties. However, MOE and MOR values decreased by approximately 30% and 60%, respectively. Treated samples resulting from the combination of chemical and thermal treatment performed at 220 °C present improved durability against the termites R. flavipes.