Abstract:

Steam heat treatment can darken wood color remarkably. There is a highly relativity among the color change degree, heat treatment time and temperatures. The specimens of Chinese White Poplar (Populus tomentosa) was steam heat- treated in an airtight equipment with an atmosphere within comprising less than 2 percent oxygen content at temperatures from 170 to 230 ℃ for time from 1 to 5 hours, respectively. Saturated steam was used as a heating medium and a shielding gas. The results showed that the chroma difference (ΔC^* ) was decreased gradually while the color difference (ΔE^* ) and hue difference (ΔH^* ) were increased with the increase of temperature and the extension of treatment time. This indicated that the color of steam heat-treated wood became darker and darker compared with original color. Compared with treatment time, treatment temperature played a more important role to change the color of heat-treated wood during the process of heat treatment according to the results of ANOVA and multiple comparison analysis. Additionally, the regression models among the color difference, treatment temperatures and times were established. The results suggested that the better color of wood could be obtained after steam heat treatment compared with original color as well as the dimensional stability would be improved. Therefore, the value of the timber could be increased and the application fields could be extended after the steam heat treatment.

Key words: Populus tomentosa, steam heat treatment, color difference