Structural Characterization of Switchgrass Lignin after Ethanol Organosolv Pretreatment

Kanlow switchgrass was subjected to aqueous ethanol organosolv pretreatment, and ethanol organosolv lignin (EOL) was recovered through precipitation of pretreatment effluents. Ball-milled switchgrass lignin was also isolated from unpretreated and pretreated switchgrass. The obtained switchgrass lignins were characterized using Fourier transform infrared (FTIR) spectroscopy, P-31 nuclear magnetic resonance (NMR), two-dimensional (2D) heteronuclear single-quantum coherence (HSQC) NMR spectroscopy, and gel permeation chromatography (GPC). The results showed that the molecular weight of switchgrass EOL lignin decreased while polydispersity increased. The pretreatment resulted in an increase of free phenolic guaiacyl and syringyl units and a decrease of the beta-O-4 linkage content.