Study on the Spectra of Spruce Lignin with Chlorine Dioxide Oxidation

The Fourier transform infrared spectroscopy (FTIR), ultraviolet-Visible spectroscopy (UV-visible), Fourier transform Raman spectroscopy (FT-Raman), and nuclear magnetic resonance spectroscopy (H-1 NMR) were used to study the oxidation of spruce lignin by chloride dioxide. The results are as following: The selective oxidation of lignin by chlorine dioxide was obtained by spectroscopy study. FTIR showed that the characteristic absorbance peak of guaiacyl unit in the lignin structure was decreased after chloride dioxide oxidation, while the peaks of syringyl and para-hydroxyphenol disappeared after oxidation. The largely increased absorbance for the band around 1 720 cm(-1) corresponding to carbonyl stretching was achieved in the oxidized lignin. The ultraviolet-visible spectroscopy showed that the absorbance around 280 nm was largely reduced after the lignin had been oxidized. The H-1 NMR spectroscopy also showed the decrease of aromatic units and methoxyl group in the oxidized lignin. These indicated the formation of ester, or quinone derivatives when the lignin was selectively oxidized by chloride dioxide.