Impact of thermal modification on properties of tropical and temperate timber species

Abstract

Climate change is putting a lot of pressure on some of the most used production species in Wallonia. To compete against concrete and steel that are not sustainable in the climate change context, wood’s natural durability against fungi and insects is important to consider for outdoor use. More durable tropical species are imported in Wallonia but tropical forest’s suffer from overexploitation of a couple timber species. Chemical treatments are found to make wood more durable but regulations and people mentality make chemical treatments hard to employed. To face those problems, it is important to find a way to add values and start using more Lesser Used Species (LUS). To make them more durable against fungi and insects and environmentally friendly when treated, thermal treatment has been developed. Four LUS (Scyphocephalium manii. Acer pseudoplatanus L., Carpinus betulus L. and Alnus glutinosa (L.) Gaertn) have been thermal treated (twice at 215 °C for 3 hours) with a VACWOOD® process. Sorro present some heartwood colour differentiation, the impact of this trait is studied in this paper. The modulus of elasticity (MOE), the modulus of rupture (MOR) and the impact bending strength (IBS) have been tested in addition to their durability against fungi (Coniphora puteanaa and Trametes versicolor) and termites (Reticulitermes flavipes). The results show a global diminution of their physico-mechanical properties after treatment. The level of diminution can be correlated with the intensity of the treatment (time and temperature). C. betulus seems to be less impacted. An important increase of fungal durability has been noticed. Durability against termites’ attacks decreased after thermal treatment for all species. Future studies should be focused on the intensity of the treatment to find a compromise between physico-mechanical properties loss and fungal durability increase. Sorro heartwood colour impact its MOE and MOR properties probably due to heartwood streaks.