Color and surface chemistry changes of extracted wood flour after heating at 120 °C

To investigate the effect of heat on color and surface chemistry of wood flour (WF), unextracted, extracted and delignified samples of commercial WF were heated at 120 °C for 24 h and analyzed by colorimetry, diffuse reflectance visible (DRV), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Fourier transform Raman (FT-Raman) spectroscopies. Unextracted samples showed a slight increase in CIEL^*a^*b^* color coordinates, a ^* and b ^*. Compared with unextracted samples, color changes of the extracted samples varied with composition of the extraction solvents with generally smaller increases in a ^* and larger decreases in b ^* values. Delignified samples were marked by even larger increases in both a ^* and b ^* values. The color changes could be explained by analysis of the respective DRV, FTIR and FT-Raman spectra of the samples before and after heating. Heating of the extracted WF at 120 °C resulted in a red shift of the absorption at 430 nm and increase in absorption in the violet-blue spectral region of visible light. Delignified samples showed even more pronounced absorption in this spectral region after heating.