Effect of thermal modification on the properties of narrow-leaved ash and chestnut

The concept of thermal modification has evolved from a challenging research program to commercial reality in several European countries in recent years. The aim of this study is to determine the change of various physical properties (oven-dry density, air-dry density, weight loss, swelling and anti-swelling efficiency (ASE)), compression strength parallel to grain, colour difference (ΔE), glossiness and surface roughness of narrow-leaved ash (Fraxinus angustifolia Vahl.) and chestnut (Castanea sativa Mill.) woods after heat treatment under different temperatures and durations. For this study two different temperatures (160 °C and 180 °C) and two different durations (2 h and 4 h) were considered. A stylus method was employed to evaluate the surface characteristics of the samples. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Four main roughness parameters which are mean arithmetic deviation of profile (Ra), mean peak-to-valley height (Rz), root mean square roughness (Rq), and maximum roughness (Ry) obtained from the surface of wood were used to evaluate the effect of heat treatment on the surface characteristics of the specimens. The properties studied were significantly different (p = 0.05) at two temperatures and two durations of heat treatment. Based on the findings of this study, the results showed that oven-dry density, air-dry density, swelling, compression strength parallel to grain and surface roughness decreases with increasing heat treatment temperature and time.

► The last decades developments in the arena of wood modification have accelerated considerably.
► This acceleration is due to a number of circumstances of which the environmental awareness, the increasing demand for high and constant quality and the increasing prices and availability of tropical hardwood species.
► Thermal modification is used to improve dimensional stability and durability of wood and wood-based materials.
► The thermal modification process has a significant factor influencing of the physical and mechanical properties of the wood-based materials.
► The improved characteristics of the thermally modified wood-based materials offer many potential and attractive new opportunities to wood products industry.