ISOLATION AND PHYSICO-CHEMICAL CHARACTERIZATION OF LIGNIN FROM HYBRID POPLAR IN DMSO/LiCl SYSTEM INDUCED BY MICROWAVE-ASSISTED IRRADIATION
نویسندگان
چکیده
In this paper, the effect of microwave-assisted heating (60, 80, 100 and 120 °C) on lignin separation from ball-milled hybrid poplar wood in dimethyl sulfoxide and lithium chloride (DMSO/LiCl) system was examined. The isolated lignin fractions were characterized by HPAEC (high-performance anion exchange chromatography), FT-IR, C NMR and 2D-HSQC NMR techniques. The results showed that extraction of lignin assisted by microwave irradiation at 60, 80, 100 and 120 °C resulted in an increase of lignin yield by 2.4, 8.8, 13.5 and 24.6% (% Klason lignin), respectively. The content of neutral sugars in these lignin fractions was relatively lower as compared with the milled wood lignin (MWL) obtained by the classical method. Structural characterization by 1D and 2D NMR demonstrated that these lignin fractions were classified as syringyl-guaiacyl lignin as they were mainly composed of syringyl units with noticeable amounts of guaiacyl units. In addition, the results of semi-quantitative NMR spectroscopy showed that these lignin fractions mainly consisted of β-aryl ether linkage (β-O-4’, 53.3-74.1%) and resinol substructure (β-β’, 15.1-28.5%) combined with small quantities of phenylcoumaran substructure (β-5’, 3.1-8.2%) and spirodienone substructure (β-1’, 3.2-8.4%).
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