Changes in chemical, physical and mechanical characteristics of three kinds of solid wood after one-sided surface charring

Surface charring is a wood modification process in which wood is charred by applying heat at high temperatures. Several tropical species from forest plantations have been widely studied for different wood modification processes in Costa Rica. This study aimed to investigate the effect of one-sided surface charring by using a heating plate at three different temperatures and determine the changes in the physical, mechanical, and chemical composition of Cupressus lusitanica, Gmelina arborea and Tectona grandis wood. The samples were placed between two metal plates and the bottom plate was heated at three target temperatures of 300 °C, 350 °C and 400 °C for 10 min, with a weight of 10 kg placed on the top plate to avoid deformations in the wood. The results demonstrated that the cellulose and lignin were not modified at 300 °C and 350°. FTIR spectrum showed a decrease in the peak associated with lignin (1434 and 810 cm^{− 1}), cellulose (1700 − 1600, 1206, 1032, 1111 and 780 cm^{− 1}) and hydroxyl groups of water (3400 and 2900 cm^{− 1}) and a slight difference in relation to the parent wood. These chemical changes increased ash content, carbon content, charring thickness and transition thickness, but decreased moisture content, density, oxygen content and volatile matter. The strain (MOE) in bending is governed by the charring thickness of the surface-charred wood, but the stress (MOR) in bending depends on the charring temperature and density.