ALKALINE DELIGNIFICATION OF HARDWOODS IN A FLOW-THROUGH REACTOR WORKING AT A LOW RESIDENCE TIME .5. CHARACTERIZATION OF SODA LIGNINS BY C-13 NMR

Fractions of Poplar lignin resulting from the soda process are characterized qualitatively and quantitatively by C-13 NMR. They result from two cooks carried out with the assistance of a fixed bed reactor working at a low residence time and, using, solutions 1 N and 0. 125 N. After extraction, the lignins arc fractioned according to cooking time, precipitated and recovered. In the case of lignin extracted using a soda solution 1 N, nine fractions of lignin are characterized by C-13 NMR. For the other series of lignin; only the representative fractions of the main stages of the delignification are analysed. The qualitative and quantitative analysis of the spectra shows an evolution in the signals of the carbons corresponding to the alkyl-aryl ether units of the lignins. and allows to establish a good correlation between beta-aryl-ether cleavages and delignification kinetics.