PHENOLIC OH GROUP ESTIMATION BY FTIR AND UV SPECTROSCOPY. APPLICATION TO ORGANOSOLV LIGNINS

Abstract

The phenolic hydroxyl group content of 34 acetylated organosolv lignins, obtained by ethanol or methanol autocatalyzed pulping of Eucalyptus globulus was measured by FTIR spectroscopy. The absorbance of aromatic IR ester bands of acetylated lignins at 1765 cm⁻¹ was employed to estimate the lignin phenolic hydroxyl group content. To compare different samples the spectra recorded were baseline corrected and normalized with the bands around 1500, 1600 and 1423 cm⁻¹. Partial least-squares (PLS) and multiple linear regression (MLR) calibrations were carried out to establish a mathematical correlation between UV data sets and FTIR spectra. The best results were shown by the models obtained by PLS regression. In these models the band at 1766 cm⁻¹ was normalized using the band at 1744 cm⁻¹ and the baseline corrections were performed with the bands at 1423 cm⁻¹ (ethanol lignin) and 1507 cm⁻¹ (methanol lignin).

Acknowledgments