Color and Surface Chemistry Changes of Pine Wood Flour after Extraction and Delignification

A detailed study was undertaken to examine the color and chemistry changes of pine wood flour when its extractives are removed and when it is delignified. The solvent systems employed were toluene/ethanol (TE), acetone/water (AW), and hot-water (HW), while sodium chlorite/acetic acid were used for delignification (i.e., lignin removal (LR)). Samples were analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, Fourier transform Raman (FT-Raman) spectroscopy, and colorimetry. The study demonstrated that color parameters (i.e., CIE L * a * b * ) were only slightly affected by the removal of extractives, but changed noticeably when extractions were followed by delignification. TE extraction was more effective at removing the yellow colored substances, whereas AW mostly removed red colored substances that contained C=O groups. Inclusion of a HW extraction step after extraction with AW (AW-HW) removed components that contained conjugated C=O structures. Inclusion of a delignification step after extraction with AW followed by HW extraction (AW-HW-LR) was effective at removing yellow substances that contained non-conjugated C=O groups.