The bidirectional regulation mechanism of NMMO concentration change on cellulose dissolution and regeneration

The dissolution and regeneration process of cellulose molecules in NMMO aqueous solution was studied by molecular dynamics (MD) simulation. The effect of the concentration of NMMO aqueous solution on the structure of cellulose was discussed. During the simulation process, the aggregation structure of cellulose molecules changed significantly, and experienced the dissolution process and regeneration process. During the dissolution of cellulose, the NMMO aqueous solution penetrates into the cellulose bundle from the cellulose O2-H2-O6 direction. NMMO around O6, O3 and O2 plays a vital role in the dissolution of cellulose. NMMO destroys the hydrogen bonds between the intra-chains of cellulose, thus making cellulose dissolved in the solvent. During the regeneration process, the concentration of NMMO aqueous solution decreased, and water molecules around the acetal oxygen atom increased, which destroyed the hydrogen bond between NMMO and cellulose, and made the cellulose single chain form aggregates. Although it eventually aggregated into cellulose bunches structure, the hydrogen bond of regenerated cellulose lacked regularity, which affected the stability of the regenerated cellulose structure.