Influence of Isolation Condition on Structure of Milled Wood Lignin Characterized by Quantitative 13C Nuclear Magnetic Resonance Spectroscopy

Milled wood lignin (MWL) was widely characterized to demonstrate the structure of native lignin by liquid state C-13 NMR. As an isolated lignin, the structure of MWL was influenced by the isolation procedure performed. In this article, hardwood (sweetgum) and softwood (loblolly pine) were subjected to various isolation conditions to elucidate the effect of extracting temperature and milling time on the structure of MWL. Purification was also carried out on the crude MWL. The structure of the crude MWL and the purified MWL was identified and quantified by C-13 NMR. Based on the yield and the lignin content of the crude MWL, the optimal isolation was achieved with 8 h milling and 20 degrees C extracting for hardwood. For softwood, the optimal isolation condition for crude MWL was 12 h milling and 20 degrees C extracting.