Characterisation of milled wood lignin from reed canary grass (Phalaris arundinacea)

Lignin samples from reed canary grass (Phalaris arundinacea) were prepared by milling in the dry state (MWL) or in toluene (TMWL). Further, enzymatically liberated lignin (EL) was prepared From the dioxane-water insoluble residue from the preparation of MWL. The NMR spectra of the lignin preparations revealed the presence of both guaincyl and syringyl units, as well as p-hydroxyphenyl structures. The most prominent side chain linkages were identified using HMQC. In the C-13 NMR and FTIR spectra signals typical for p-coumaric esters could be observed. Permanganate oxidation revealed that some of the p-hydroxyphenyl structures were incorporated in the lignin, together with guaiacyl and syringyl units. The lignin preparations had very similar molecular weight distributions and structural composition. These lignin preparations are distinguished by high amounts of beta-O-4 structures and by low amounts of phenolic hydroxyls, resinol units (beta-beta) and of condensed units (beta-5 and 5-5). This trait was even more pronounced in an ether soluble fraction of the MWL that contained almost exclusively ide chain linkages of the beta-O-4 type. This difference in distribution of structural units indicates some structural heterogeneity in reed canary grass lignin.