Structure elucidation and properties of different lignins isolated from acorn shell of Quercus variabilis Bl.

Abstract

Chemical and structure properties of Ethanol lignin (EL), alkali lignin (AL), milled wood lignin (MWL) and cellulase enzymatic lignin (CEL) extracted from acorn shell of Quercus variabilis Bl. was studied by GPC, TG, SEM, FT-IR, 13C NMR, DEPT-135 NMR, 2D-HSQC and functional groups measurement. Results indicated that AL had a lower quantity of ArOH (2.19mmol/g) in four lignin samples. TG results proved the existence of a less thermally stable domain within the lignin polymer. SEM, FT-IR, 13C NMR, DEPT-135 NMR and 2D-HSQC confirmed the lignin structural characters of the extracted samples, it was found that the relative content of β-O-4′ linkage in MWL (51.15%) was lower than that of in EL(55.83%), AL (57.93%) and CEL (64.81%), suggesting that β-O-4′ linkage was cleaved greatly during the milled wood lignin isolation process. AL had a higher S/G ratio than EL, MWL and CEL. The indentified substructures are plotted depended on the spectrogams. The differences in the composition of the lignin samples further supported that the deposition of lignin in the shell of Q. variabilis is inhomogeneous. In short, these findings will enhance our understanding of native lignin in acorn shell and theoretical foundation is laid for the further study of degradation.