CHARACTERIZATION OF HEARTWOOD LIGNIN FRACTIONS FROM QUERCUS-ROBUR L. AND QUERCUS-PETRAEA (MATT) LIEBL., THE MAIN OAK SPECIES USED FOR BARREL MAKING

Various methods were used to characterize three kinds of lignin fracti ons from the heartwood of Quercus robur and Q. petraea. UV analysis an d determination of the mean molecular mass showed that the first fract ion, soluble in a hydroalcoholic medium and extractable with dichlorom ethane, is a mixture of oligomer lignins with a mass below 800 Da, hig hly enriched with free phenol aldehyde and lyoniresinol. The LE and LD fractions, extractable with ethanol and dioxane, respectively, are re latively pure lignins. LE and LD thioacidolysis products, and LE sine contains ellagic acid. IR and GC-MS analysis of their thioacidolysis p roducts enabled us to demonstrate the heterogeneity of these two ligni ns. LE is characterized by an S/G close to I,while LD has an S/G ratio between 1.41 and 1.67, characteristic of lignins rich in syringyl uni ts.