Color and chemical changes in teak (Tectona grandis L. f.) and meranti (Shorea spp.) wood after thermal treatment

This paper studied the effect of thermal treatment (160 °C, 180 °C, and 210 °C), based on ThermoWood® principle, on the color and chemical properties of teak (Tectona grandis L. f.) and meranti (Shorea spp.) wood. The color of the wood was determined using the CIE L*a*b* system before and after the thermal treatment and was evaluated according to the total color change. The chemical changes were evaluated by wet chemical methods. The lightness of the wood was most affected during treatment. Meranti wood became darker (46.1%) compared with the teak wood (41.8%). The red-green and yellow-blue coordinates were higher in the teak wood, and their values decreased as the thermal treatment temperature increased in both wood species compared with untreated wood. The color change was higher in the meranti wood, and it increased steadily with increasing temperature. The extractives, cellulose, and lignin percentage contents increased in both wood species; however, the highest treatment temperature of 210 °C decreased the lignin in the meranti wood. The least stable component in both wood species was the hemicellulose. The hemicellulose content in the teak wood decreased by 67.7%, while it decreased by up to 80.5% in the meranti wood.