Structural analysis of residual and technical lignins by H-1-C-13 correlation 2D NMR-spectroscopy

Structural analysis was conducted on residual lignin from pine Kraft AQ pul p, Eucalyptus Kraft lignin from Eucalyptus globulus and Repap Organosolv li gnin by 2D C-13-H-1 correlation NMR spectroscopic techniques such as HMQC s equence. These lignins contain a rather wide variety of saturated aliphatic groups. The HMQC NMR spectra of the lignins do not verify the presence of diarylmethane moieties in any lignin investigated. The type and amount of o ther condensed structures depend on the nature of lignin preparation. All t he lignins investigated still contained beta -O-4', pino- and syringayresin ol (beta-beta') and phenylcoumarane (beta -5') structures. Stilbene structu res were also identified. Vinyl ether structures were present only in Eucal yptus Kraft lignin. All the lignins contain a-carbonyl groups conjugated to aromatic moieties as terminal side chains rather than involving beta -O-4' structures. No coniferyl alcohol and coniferyl aldehyde type structures ar e detected in the lignins after pulping. The spectra of kraft lignins show some new signals, the origin of which is discussed.