NEW INSIGHTS INTO THE MOLECULAR ARCHITECTURE OF HARDWOOD LIGNINS BY CHEMICAL DEGRADATIVE METHODS

Lignins are composed of phenylpropane units interconnected by labile and resistant bonds. A two-step degradation, thioacidolysis, provides detailed information on these network polymers. The fist step involves lignin depolymerization with ethanethiol and BF3 etherate. The determination of the recovered thioethylated monomers provides an estimation of lignin units only involved in labile ether bonds. The lignin-derived dimers, representative of resistant interunit bonds, are determined after a further desulfurization step. Results obtained for native and industrial hardwood lignins underline their structural differences. Native hardwood lignins are typified by a high proportion of linear fragments linked bifunctionally by beta-O-4 bonds.