Lignin Structural Modifications Resulting from Ethanol Organosolv Treatment of Loblolly Pine

Milled wood lignin samples from untreated Loblolly pine, post-ethanol organosolv pretreatment, and ethanol organosolv dissolved lignin were isolated and characterized by quantitative 13 C and 31 P nuclear magnetic resonance (NMR) spectroscopy. β-O-4 linkages are the predominant substructures present in lignin from the starting material, as well as after the pretreatment. During organosolv treatment of Loblolly pine, acid-catalyzed cleavage of β-O-4 linkages and ester bonds were the major mechanisms of lignin cleavage. This degradative pathway results in the formation of a dissolved ethanol organosolv lignin, which is more condensed and has a lower molecular weight than the starting lignin. The residual lignin isolated from the solid pretreated residue was also more condensed. Results from quantitative 13 C and 31 P NMR show that the residual and dissolved lignin fractions after pretreatment have a higher abundance of phenols and carboxylic acids and lower aliphatic carbon content and may be suitable as antioxidants or other value-added lignin products.