EFFECT OF TEMPERATURE ON THE COLOR CHANGES OF WOOD DURING THERMAL MODIFICATION

This paper deals with the determination of color change for oak, birch and pine wood. Color changes were measured on native and thermally modified wood. The thermal modification was carried out at four different temperatures: 160 degrees C, 180 degrees C, 210 degrees C and 240 degrees C. Color changes were evaluated according to CIE L*a*b* method by parameters L*, a*, b* and Delta E*. After the heat treatment, the lightness L* of wood was reduced for all wood species. The a* values had a similar character for oak and birch wood, while the values of pine showed an opposite character. Increasing the temperature resulted in a decrease in the values of the parameter b* for oak and birch wood. However, pine wood achieved the highest b* values during thermal modification at a temperature of 160 degrees C. Further increases in temperature led to a gradual lowering of these values. The overall color change Delta E* gradually grew with the increase in temperature for oak and birch, while pine had the highest value at a temperature of 160 degrees C.