Physical and Mechanical Properties of Fast-Growing Wood Subjected to Freeze-Heat Treatments

Abstract

The physical and mechanical performance of wood from the rose gum (Eucalyptus grandis) and the Gympie messmate (Eucalyptus cloeziana) species were investigated. The wood samples were treated with a two-stage freeze-heat thermal process. Fast-growing trees were used for preparing test samples, which were subjected to thermal treatments. The freezing stage had the treatment temperature fixed at -22 °C for 72 h, while the temperature of the heat stage ranged from 180 to 200 °C for 3.5 h. The measurements of mass loss, density, and equilibrium moisture content were determined to better understand the mechanical properties. Static bending, compression parallel to grain, Janka hardness, and impact tests were applied to reveal changes in the mechanical behavior of the treated wood. In general, the freezing stage decreased the mass loss and increased the moisture content of wood (when combined with the heating stage), which showed the opposite trend for the heating stage. Modulus of elasticity and compression strength were increased only after the heating stage, while decrements were found for modulus of rupture, impact strength, and Janka hardness. The two-stage treatments did not prevent a decrease in the mechanical properties; however, they were helpful in preventing higher mechanical resistance losses in hardness (the Gympie messmate) and impact resistance (the rose gum).