Purification, Structural Characterization, and Modification of Organosolv Wheat Straw Lignin
journal contributionposted on 2015-06-03, 00:00 authored by Laurie Mbotchak, Clara Le Morvan, Khanh Linh Duong, Brigitte Rousseau, Martine Tessier, Alain Fradet
Biolignin, a wheat straw lignin produced by acetic acid/formic acid/water hydrolysis, was characterized by 31P and 13C–1H 2D NMR spectroscopy and by size-exclusion chromatography. Biolignin is a mixture of low molar mass compounds (Mn = 1660 g/mol) made up of S, G, and H units and of coumaric and ferulic acid units. β-5 and β-O-4 interunit linkages are partially acylated in the γ-position by acetate and p-coumarate groups. Deacylated samples with a low content of contaminants were obtained by combining alkaline hydrolysis and solvent extraction. The high phenolic OH content found by 31P NMR reflects the presence of condensed aromatic units, such as 5–5 units. Reaction of purified lignin with ethanol and ethane-1,2-diol yielded esterified lignins much more soluble than Biolignin in common organic solvents. During this reaction, the secondary OH of β-O-4 linkages was simultaneously etherified. Phenol hydroxyethylation by 2-chloroethanol yielded samples containing only aliphatic hydroxyl groups.