CLASSIFICATION OF LIGNINS FROM DIFFERENT BOTANICAL ORIGINS BY FT-IR SPECTROSCOPY

A classification system of lignin spectra is presented, based on FT-IR spectroscopy of more than hundred MWL's. The spectra were baseline corrected and normalized. Three main categories can be differentiated: (1) G type, (2) GS type, and (3) HGS type. The spectra within the GS category constitute a continuum, but they can be further subdivided into four groups. The classification criteria are presented as a table and illustrated by authentic FT-IR spectra obtained from MWL's. Peak-peaker lists of typical representatives of the three principal groups show the band intensities of normalized IR spectra. A triangular coordinate system displays the correlation between the spectral features on the one hand, and the possible composition of a lignin from its H, G, and S units on the other.