(288e) Fractionated Lignin Rheology and Structure

Critical technological challenges remain in the development of commercially viable lignin extraction and utilization processes to yield high value commodity chemicals and novel materials such as aromatics, polymers, adhesives, and flavorings. Processing strategies need to be developed for chemical and enzymatic degradation methods, catalytic upgrading, and purification to make it feasible for commercialization. Designing strategies to process multiphase lignin slurries requires understanding the slurry characteristics, especially quantification of the rheological properties. Fractionating heterogeneous lignin structures yield relatively homogeneous sets that offer simpler processing strategies as compared to inherently heterogeneous whole lignin. The objective of this work was to characterize rheological measurements of fractionated lignin and correlate the rheology to fractionated lignin structures. Organosolv and Kraft lignins were fractionated into five fractions using solvents of increasing polarity. Rheology of lignin fractions dissolved in DMSO was characterized with a rheometer programmed to sweep a range of shear rates for non-Newtonian slurries. ¹³C nuclear magnetic resonance (NMR) analysis was performed to determine changes in structure and functional group contents of each fractional set. Non-Newtonian behavior increased with increasing lignin concentration within any fractionated group. Although structure varied, there were no obvious rheological differences across solvents or lignin types.