Color Change and Consumer Preferences towards Color of Heat-Treated Korean White Pine and Royal Paulownia Woods

Heat treatment of wood is an attractive alternative environmentally-friendly treatment to add value of less valuable woods by improving color, dimensional stability, and natural durability. To improve the color properties of Korean white pine (Pinus koraiensis) and royal paulownia (Pauwlonia tomentosa), we treated the woods at $160^{\circ}C$, $180^{\circ}C$, $200^{\circ}C$, and $220^{\circ}C$ for 2 hours. Color change after heat treatment was evaluated using the CIE-Lab color system and survey was conducted to determine the consumer preferences towards color of heat-treated wood. Lightness ($L^*$) decreased with increasing temperature and the higher degree of change was obtained in royal paulownia. The red/green chromaticity ($a^*$) in both wood decreased after heat treatment at $160^{\circ}C$, and constantly increased after heat treatment at $180^{\circ}C$ to $220^{\circ}C$. Yellow/blue chromaticity ($b^*$) in Korean white pine tended to increase after heat treatment at $160^{\circ}C$, then decreased gradually afterwards. In royal paulownia, $b^*$ values linearly increased with increasing temperature. Overall color change (${\Delta}E^*$) increased with increasing temperature with higher degree obtained in royal paulownia. Samples with the clamps in both wood species showed lower degree of the change in $L^*$, $a^*$, b and ${\Delta}E^*$. The results of the consumer preferences test showed that the darker colors of heat-treated woods were more preferred by consumers compared to the lighter colors of untreated woods. Consequently, heat treatment could enhance the color properties of Korean white pine and royal paulownia woods for value added products.