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 ionic liquid by anti-solvents (water, ethanol and acetone) were investigated by molecular simulations. Cellulose model consists of seven glucose single chains were constructed. In order to depict the regeneration mechanism, both the dissolution and regeneration processes of cellulose in [Bpy][OAc] IL were simulated. The methyl hydroxyl group of cellulose will change its conformation during dissolution and regeneration. The conformation of initial cellulose crystal is mainly the tg conformation. After dissolved in ILs, the cellulose conformation changes into the gt conformation and the gg conformation. After regenerated by anti-solvent, the proportion of the gg and gt conformation changes, and the gg conformation increased and the gt conformation decreased. Based on energy analysis, it is concluded that the energy for tg is the lowest, and the tg widely exists in cellulose I. After cellulose is dissolved in ILs, the conformation changes into two higher energy conformations, the gt and gg. In the subsequent regeneration process, with the completion of regeneration, the gg conformation increases and the gt conformation decreases.