Thermal modification’s influence on the color of Tectona grandis L.f. sapwood to resemble heartwood

The commercial value of teak wood is associated with its heartwood, which has a naturally darker color than sapwood. To reduce this color disparity, thermal modification can be used to homogenize the color between sapwood and heartwood by minimizing color differences. This research aimed to assess the effectiveness of thermal modification in making the color of teak sapwood similar to that of heartwood. Thermal modification was carried out at 160, 180, 200, and 220 °C for 150 min. Thermal modification of teak sapwood at 180 °C ensured greater color similarity to the heartwood of a fast-growing 16-year-old plantation. The material darkened with increasing process temperature. There was a change in the content of soluble substances, and hot water extraction had greater correlations with hue angle, lightness, and yellowness. Thermal modification also reduced the number of hydroxyl groups and improved the wood’s thermal stability.