FTIR spectroscopy is a well known method for elucidating the structures of lignin samples. Determination of the ratio between the content of C=O groups and aromatic structures in lignin samples is an important aid to monitoring the degree of delignification during different pulping and bleaching procedures. In the present work a semiquantitative method is described in which calibration mixtures with eight different ratios of tartaric acid to milled wood lignin are prepared in order to account for the different responses of the aromatic band at 1510cm-1 and the C=O band at 1740cm-1. From the calibration function obtained it is possible to calculate the results in mmoles of C=O/g aromatic lignin. The method is tested on residual lignins and spent liquor lignins from pulps with different degrees of delignification.
- Carbonyl group
- IR spectroscopy