Mechanism and conformation changes for the whole regeneration process of cellulose in pyridinium-based ionic liquids

In this work, mechanism and conformation changes of cellulose regenerated from the ionic liquid by anti-solvents (water, ethanol and acetone) were investigated by molecular dynamics simulation. To explore the regeneration mechanism, a cellulose model with seven glucose chains was constructed, both the dissolution and regeneration processes of cellulose in N-butyl pyridinium acetate ([Bpy][OAc]) were simulated. Firstly, compared to the effects of the three anti-solvents on cellulose regeneration, water is the best anti-solvent. The reason is that water has a strong ability to break the hydrogen bonds between cellulose and ionic liquid. Secondly, the methyl hydroxyl group of cellulose will change its conformation during dissolution and regeneration. After the dissolution in ILs, the conformation of cellulose transforms from tg to gt and gg. After the regeneration with anti-solvents, the proportion of the gg conformation increases and gt conformation decreases. The results will provide theoretical basis for optimizing cellulose regeneration process, and help to further explore and expand the application of ionic liquids.