Chemical Structure Elucidation of Populus deltoides MWL and EL Lignins

The structure of Enzymatic Lignin (EL) was elucidated and compared to conventional Milled Wood Lignin (MWL). The method was based on the hydrolysis and solubilization of wood xylan and cellulose using combination of xylanase, cellulase and glycosidase, followed by lignin purification using alkaline protease and extraction of lignin with dimethylacetamide (DMAc). The chemical structure of Enzymatic Lignin (EL) was elucidated and compared to conventional Milled Wood Lignin (MWL) using wet chemical analysis, FTIR and Quantative 13C NMR, GC/MS and degradative techniques. The results indicate the less degradation during EL degradation compared to MWL. Comparing to conventional enzymatic extraction procedures, using an enzymatic sequence with reduced milling time can ensure a relatively pure lignin with small structural changes. Analytical results showed that Popolus deltoides wood has a more 4-(3-hydroxy-1-propenyl)-2-methoxy phenol units (guayacil lignin) regarding to 4-(3-hydroxy-1-propenyl)-2,6-dimethoxy phenol units (syringyl moieties). The residual lignin is mainly composed of condensed structures which often are complexed with carbohydrates. Also, the enzymatic lignin structural analysis through GPC and GC revealed the less condensation structure regarding to MWL which is due to less degradation during isolation process.