Colorimetric and thermochromic properties of reversible thermochromic wood
To endow wood materials with a thermochromic function, an organic thermochromic agent consisting of thermochromic dye, bisphenol A (BPA) and long-chain alcohols (1-tetradecanol (TD), or 1-hexadecanol (HD)) was used as a dye to prepare reversible thermochromic wood (RTCW). The colorimetric properties, including total color difference (ΔE*ab), lightness index (L*), red-green index (a*), and yellow-blue index (b*), were investigated at different temperatures. The color change temperature range and color hysteresis of RTCW were also analyzed. The color difference unit of National Bureau of Standards (NBS) was used to determine the color change temperature range and the achromic (chromic) temperature. In the decolorization process, with the temperature increasing, the values of ΔE*ab, L* and b* of the RTCW samples increased, and the values of a* decreased, but the values of ΔE*ab, L*, a*, and b* were just opposite in the colorization process. Meanwhile, the color of the RTCW with TD or HD could repeatedly change between red and light brown (wood colore) within a color temperature range of 25-35°C or 37-49°C respectively, presenting a “color hysteresis” phenomenon over a heating (decolorization) and cooling (colorization) cycle. The achromic and chromic temperature of the RTCW samples with TD was 31°C and 25°C respectively while RTCW samples with HD was 43°C and 37°C.