AbstractThermally-modified wood is not sufficiently durable for exposure to environments in which severe biological deterioration is likely. So in this study, samples of southern yellow pine sapwood were first subjected to thermal modification and then impregnated with the alkaline copper quat-type D (ACQ-D) wood preservative. Three heating temperatures (180, 200, and 220 °C) and two concentrations of ACQ-D solution (0.90% and 1.35%) were used in the experiments. The copper retention, percentage of copper leaching, and concentrations of copper ions in the leachates collected during the leaching tests were evaluated using inductively coupled atomic emission spectrometry (ICP-AES). Fourier transform infrared spectroscopy (FTIR) analysis was also used to interpret the differences in leaching performance between thermally-treated and unheated wood samples. The pseudo-second-order model of copper leaching was developed with the experimental leaching data, which could determine the amounts of copper ion leaching and predict the final percentage of copper leaching during the leaching process. As a result, compared to the control group, the copper retention of the thermally- modified wood samples was lower, while the percentage of copper leaching was higher. This observation could be explained by the lower number of copper ion fixation sites in the thermally-treated wood.