Thermal modification is an effective method to improve the dimensional stability of wood by reducing its hygroscopicity. In this study, the effects of thermal treatment on the moisture sorption behavior and dimensional stability of pine wood were investigated. Specimens were treated at 170°C and 200°C for 1, 3, and 5 h, and adsorption isotherms were obtained at 20°C over a relative humidity (RH) range of 40–95%. The equilibrium moisture content (EMC) of thermally treated specimens decreased across the entire RH range compared to the control, with the reduction becoming more pronounced at higher RH levels. The GAB model successfully described the adsorption behavior, and the monolayer moisture content () and constant decreased with increasing treatment severity, indicating a reduction in the number and strength of moisture sorption sites. Radial and tangential swelling also decreased significantly after thermal treatment. At 95% RH, EMC decreased by up to 35.2%, while radial and tangential swelling decreased by 37.0% and 37.7%, respectively. The reduction in swelling was comparable to or slightly greater than that in EMC. A strong positive relationship between ΔEMC and ΔSwelling was observed, confirming that dimensional changes are primarily governed by moisture content. These results demonstrate that thermal modification enhances the dimensional stability of pine wood mainly through reduced hygroscopicity, with an additional contribution from structural changes in the cell wall.

Abstract
Introduction
Materials and Methods
    1. Specimen preparation
    2. Thermal treatment
    3. Adsorption experiment
    4. Moisture content measurement
    5. Swelling measurement
    6. Reduction in equilibrium moisture content (ΔEMC)
    7. Reduction in swelling (ΔSwelling)
    8. Application of the GAB model
Results and Discussion
    1. Adsorption isotherms
    2. GAB model analysis
    3. Radial and tangential swelling behavior
    4. Reduction in EMC and swelling
    5. Mechanism: combined hygroscopic and structuraleffects
References

• Jong Bum Ra(Professor, Department of Interior Materials Engineering, Gyeongsang National University, Jinju, Gyeongnam, 52725, Korea) Corresponding author