Title
Structural characterization of lignin from native kraft and soda-AQ pulping of Pennisetum sinese Roxb. (P. sinese)
Authors
JIACHUAN CHEN FENG SHEN GAOJIN LYU GUIHUA YANG NAN LU and CHANGQING HU

Received February 23, 2017
Published Volume 52 Issue 5-6 May-June
Keywords lignin, EMAL, P. sinese, ³¹P-NMR, 2D-HSQC NMR

Abstract
Lignins isolated from native Pennisetum sinese Roxb. (P. sinese) and black liquor from kraft and soda-AQ pulping processes were characterized and compared by the analysis of alkaline nitrobenzene oxidation/HPLC, FT-IR, 31P-NMR and 2D-HSQC NMR. The purpose was to distinguish lignins’ structural differences and explore the mechanisms in the pulping process. Major functional groups and lignin linkages (β-O-4', β-β', β-5' etc.) were identified, and the structure of P. sinese lignin was described as a typical GSH-type lignin. Enzymatic mild acidolysis lignin (EMAL) contained a predominant proportion of syringyl units and guaiacyl units (syringyl/guaiacyl ratio of 1.2-1.4), along with a large amount of associated p-coumarates and ferulates. Soda-AQL and KL showed a significant decrease in β-O-4' linkages, while β-β' and β-5' linkages appeared to be especially resistant during the pulping process. In addition, an obvious decrease in aliphatic hydroxyl and a significant increase in total phenolic hydroxyl were noted after kraft and soda-AQ pulping.