From lignin subunits to aggregates: insights into lignin solubilization

A fundamental understanding of lignin solubilization offers structural information that would benefit a variety of value added applications. Small angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) spectroscopy were used to study correlations between the functional groups/substructures and solution structures of lignin in DMSO-d(6) and 0.1 N NaOD. Three types of alkaline lignins (Sigma-Aldrich kraft lignin, poplar wood kraft lignin, and corncob soda lignin), exhibiting different degrees of aggregation in 0.4 wt% solutions, were investigated to identify the major intermolecular interactions that cause lignin aggregation. Intermolecular hydrogen bonding, non-covalent pi-pi interactions between phenyl rings, lignin chain conformation and the degree of branching were discussed. Different operating forces for lignin solubilization and aggregation were found in DMSO-d(6) and NaOD solutions.