Molecular Origins of Lignin–Cellulose Interactions: Entropic Driving Forces, Surface Dependence, and Solvent Effects

Abstract

Lignin–cellulose interactions affect biomass strength and the efficiency of biorefinery fractionation. All-atom molecular dynamics simulations and umbrella sampling were used to quantify the adsorption free energies of three lignin dimers (β-O-4, β-5, β-β), three hexamers of varied linkage composition, and a xylan-based hemicellulose onto the hydrophilic (110) and hydrophobic (200) surfaces of crystalline cellulose Iβ in water and in 80% (v/v) acetone–water. In water, both lignin and hemicellulose adsorb preferentially onto the (200) surface through an entropy-driven mechanism arising from the release of ordered interfacial water. Adding acetone lowers adsorption free energies on both surfaces and largely equalizes their thermodynamic contrast by averaging the entropic and enthalpic contributions. Hexamers absorb more strongly than dimers owing to a greater number of aromatic ring contacts, independent of linkage sequence. These results offer molecular-level guidance for organosolv fractionation and lignin nanoparticle formation.