Tuesday, April 30, 2013
Exhibit Hall
Lignin and the hemicelluloses in biomass are natural barriers that prevent cellulases from accessing cellulose and hydrolyzing it into glucose. The role of lignin in affecting enzymatic cell wall hydrolysis after pretreatment is still unclear. In general, lignin removal correlates with increased digestibility; however, some reports indicate that too much lignin removal causes a decrease in digestibility, presumably due to collapse of the cellulose macrofibers. We have previously shown a clear correlation between thermochemical pretreatment severity and the degree of surface and intra-cell wall lignin coalescence. It has also been shown that removing redeposited (surface) lignin after pretreatment by 1,4-dioxane increases enzymatic digestion of the cellulose. It is logical to now ask; does an increase in the removal of the intra-cell wall lignin also correlate with an increase in the enzymatic cellulose conversion? Methods were developed to selectively extract the surface fraction and intra-cell wall fractions of lignin from dilute acid pretreated biomass. The mass balances of these extracted lignin fractions obtained gravimetrically appear to be very reproducible. Variations in the fractionated lignin structures characterized by NMR indicated minor chemical bond linkage differences; however GPC analysis has clearly shown a difference in the extracted fraction’s molecular weights.