No abstract

No abstract

Summary Residual lignins of Eucalyptus globulus kraft pulp were shown to be structurally different depending upon the type of extraction chosen. Enzymatic hydrolysis releases a residual lignin with a well preserved etherified structure but substantially contaminated by protein and carbohydrate moieties coming from the enzyme. Moreover, the extraction yield is poor and obviously it does not work as well as in the case of softwood kraft pulp. The residual lignin extracted by acid hydrolysis has less etherified units and more free phenolic functions than that of the enzymatic hydrolysis. It contains some unsaturated structures but no carbohydrate contaminants. Comparison with Milled Wood Lignin (MWL) treated under the acid hydrolysis conditions shows that ether splitting occurs during this extraction. The different residual lignin fractions were characterised by HPSEC, FT-IR, 13C NMR and sugar analysis.

Summary The amount of carbonyl groups in an organosolv lignin was determined by 19F NMR spectroscopy after different derivatizations: derivatization with trifluoromethylphenylhydrazine, fluorobenzoylation of alcohol groups formed after NaBH4 reduction of lignin, fluorobenzoylation of phenolic hydroxyl groups after catalytic hydrogenation of lignin. Oximation was also used for comparison. Carbonyl group contents determined by 19F NMR after trifluoromethylphenylhydrazine derivatization were in good correlation with results from other methods. Trifluoromethylphenylhydrazine derivatization is a fast and easy technique, which provides a distinct quantification of aldehyde, ketone and quinone groups. Some round robin lignins (Milne et al. 1992), using trifluoromethylphenylhydrazine derivatization and modified oximation (Zakis 1994) provided significantly higher carbonyl group contents than the round robin test data, which had been measured either by classical oximation or by reduction-UV methods. Other recently reported carbonyl group estimations on round robin lignins (Faix et al. 1998; Ahvazi et al. 1999) were either in agreement or in disagreement with the herein-presented results. This indicates that carbonyl group analysis in lignins is difficult and that care must be taken when selecting an appropriate method.