Properties of heat-treated ash wood

Ash wood is characterised by high mechanical and technological properties and has a beautiful texture, which leads to a high demand for furniture and joinery products made from it. However, the widespread and rapid spread of the fungal disease Hymenoscyphus fraxineus (chalar necrosis) and the invasive beetle Agrilus planipennis caused massive dieback of ash trees. All of this led to the transformation of healthy wood during one year into low-quality “deadwood” and limited its use in industry. The objective of the research was to investigate specific properties of ash deadwood subjected to sterilisation through high-temperature treatment using various thermal regimes. To renew its use, it is proposed to use sterilisation without the addition of chemicals by thermal modification at temperatures of 185 °C (schedule 1) and 195 °C (schedule 2), which does not impair the environmental properties of wood.  The physical, mechanical, and technological properties of heat-treated ‘deadwood’ ash and healthy wood dried at a temperature of t ≤ 70 °C were studied. It has been determined that the equilibrium moisture content of heat-treated ‘deadwood’ ash wood decreased by 3.5-4.0% compared to healthy wood; the density at actual moisture and in a completely dry state decreased by 8-12% and by 4-9%, shrinkage in the transverse direction by 53-67%; the bending strength decreased by only 6 % in the case of schedule 1 and by 20% in the case of schedule 2. The static hardness in both the tangential and radial directions had an unexpected trend – an increase of 9-12% when using schedule 1 and a decrease of 1.7-13% when treated by schedule 2. The weight loss of samples of heat-treated ‘deadwood’ ash wood was 60-90% less than the weight loss of healthy wood. The accuracy factor of all experimental studies did not exceed 5%. The results obtained make it possible to effectively choose the use of heat-treated ‘deadwood’ ash wood under schedule 1 in joinery and furniture products, and treated under schedule 2 in furniture products such as tabletops, as there is a decrease in the relevant mechanical properties. The use of both treatment modes allows the use of low-cost ash wood in products that are used outdoors