Enhanced potential of fast-growth Eucalyptus woods for construction: two-step thermal treatment under dual atmospheres

Abstract

This study evaluated the effects of one-step and two-step thermal modifications on the chemical, physical, and mechanical properties of two Eucalyptus species under different atmospheres. Specimens underwent 27 treatments involving soybean oil immersion, oven heating, and combined methods at 150, 200, and 250 °C for 2, 4, and 6 h. Oil-based treatments were performed in a laboratory oil bath, while air-based treatments used a forced-air oven. Chemical properties were analyzed via wet chemical tests and FTIR, while physical properties, such as mass loss, equilibrium moisture content, and dimensional stability, were measured. Mechanical properties were determined by static bending tests and thermogravimetric analyses. Results indicated that oil-based treatments had less impact on chemical changes compared to air-based treatments. Significant modifications in wood components (hemicelluloses, cellulose, lignin, and extractives) were observed. Treatments involving oil immersion and combined immersion/air-based methods increased bulk density, especially at temperatures above 200 °C for 4 h, with increases up to 36.51%. The greatest improvement in modulus of elasticity (MOE) occurred at 200 °C for 2 and 4 h, with increases of 2.07% for Eucalyptus grandis and 2.42% for Eucalyptus saligna. Modulus of rupture (MOR) showed no increases; however, oil immersion at 150 °C resulted in the least MOR reduction (7.18% for E. grandis, 1.74% for E. saligna). Two-step processes exhibited promising potential for industrial scaling, with Eucalyptus grandis performing best overall.