Molecular origin of high-concentration cellulose dissolution in organic acid media: a combined experimental and computational study

Abstract

High-molecular-weight cellulose (CL) is generally insoluble in most common solvents due to its dense hydrogen-bonding network. In this study, we investigate the molecular origin of cellulose dissolution in two simple organic acids, formic acid (FA) and pyruvic acid (PA), which enable unusually high CL solubility, using a combination of experimental (infrared (IR) spectroscopy and high-energy X-ray total scattering (HEXTS)) and computational (density functional theory (DFT) calculations and all-atom molecular dynamics (MD) simulations) approaches. IR and DFT results reveal that FA and PA react with hydroxyl groups on the cellulose backbone, forming formyl and ester derivatives, primarily at the C6 and C2 (or C3) positions. These covalent modifications disrupt the native hydrogen-bonding network and alter the solute–solvent interaction landscape. HEXTS experiments, aided by MD simulations, further demonstrate that the modified cellulose chains are thermodynamically stabilized through directional hydrogen bonding with unreacted solvent molecules. These results provide molecular-level insights into the dual role of FA and PA as both reactive solvents (via chemical modification) and stabilizing solvents (via solvation), offering a new physicochemical perspective on cellulose dissolution in nontraditional media.