LAUSR

Abstract Wood is commonly used for making musical instruments. During the process it is often subjected to treatments, that either modify its volume or its surface properties. Spruce wood specimens were treated under mild temperatures 130 °C and 150 °C and different relative humidity from 0% to 25%. Longitudinal (L = 150 × R = 12 × T = 2.5 mm) and radial Spruce specimens (R = 120 × L = 12 × T = 2.5 mm) were treated in reactors maintained at a temperature of 130 or 150 °C, and a relative humidity (RH) of 0% or varying between 0% and 25%. Weight loss (WL), equilibrium moisture content (EMC), density (□) and vibration properties in bending (E/□, tan□), were measured before and after treatment, while color parameters were recorded also at intermediate steps. After treatments, reconditioning was applied to indicate the irreversible effects of treatments. Reconditioning was done with applying a cycle of different humidity from the first point after treatments to the same point after applying a complete cycle of humidity. EMC reduced significantly for all the treatments. Weight loss (WL) increased insignificantly while the colour parameter, L*, decreased dramatically. Tanδ reduced significantly while the E/d has increased. After reconditioning, the partially reversibility has been achieved for EMC, tanδ and E/d. But, still an irreversible changes remains, which suggested being due to the chemical changes in wood polymers. While reversible changes has been resulted from the annealing of amorphous polymers. Since, the mild hygrothermal treatment applied to the specimens coincided with no significant WL, there was no obvious damage in wood structure while the irreversible changes present an improvement in vibrational properties by decrease in damping (tanδ), which could be due to the intermediate relative humidity of the treatment.