Structure and Reactivity of Spruce Mechanical Pulp Lignins. IV: ¹³C-NMR Spectral Studies of Isolated Lignins

Abstract

¹³C-NMR spectroscopy has been used to characterize the lignins extracted by an organosolv flow-through process from spruce TMP, bleached TMP (BTMP) and yellowed BTMP (YBTMP). In general, the ¹³C-NMR spectra of these lignins are similar to that of spruce MWL, indicating that the lignins underwent limited structural changes. Thus they may be an acceptable substrate for lignin structural study. However, these lignins appear to have a significant amount of condensed aromatic carbons assigned mainly to β-5, 5-5 and diarylmethane structures. These were likely formed during the organosolv cook, or initially present in TMP and extracted with this organosolv process. On the other hand, the hydrogen peroxide bleaching causes little change in the lignin overall structure. As a favorable effect, elimination of the coniferaldehyde structures can clearly be seen. The photoyellowing appears to result in the creation of aromatic carbonyl and carboxyl groups. This suggests that oxidative cleavage of Cα, Cβb bonds is one of the important photodegradation reactions of lignin.

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Danielle Robert

Affiliated with the Universite Joseph Fourier, Grenoble, France