Dissolving process of a cellulose bunch in ionic liquids: a molecular dynamics study

Abstract

In recent years, a variety of ionic liquids (ILs) were found to be capable of dissolving cellulose and mechanistic studies were also reported. However, there is still a lack of detailed information at the molecular level. Here, long time molecular dynamics simulations of cellulose bunch in 1-ethyl-3-methylimidazolium acetate (EmimAc), 1-ethyl-3-methylimidazolium chloride (EmimCl), 1-butyl-3-methylimidazolium chloride (BmimCl) and water were performed to analyze the inherent interaction and dissolving mechanism. Complete dissolution of the cellulose bunch was observed in EmimAc, while little change took place in EmimCl and BmimCl, and nothing significant happened in water. The deconstruction of the hydrogen bond (H-bond) network in cellulose was found and analyzed quantitatively. The synergistic effect of cations and anions was revealed by analyzing the whole dissolving process. Initially, cations bind to the side face of the cellulose bunch and anions insert into the cellulose strands to form H-bonds with hydroxyl groups. Then cations start to intercalate into cellulose chains due to their strong electrostatic interaction with the entered anions. The H-bonds formed by Cl(-) cannot effectively separate the cellulose chain and that is the reason why EmimCl and BmimCl dissolve cellulose more slowly. These findings deepen people's understanding on how ILs dissolve cellulose and would be helpful for designing new efficient ILs to dissolve cellulose.

Preparation of Nanocellulose Using Ionic Liquids: 1-Propyl-3-Methylimidazolium Chloride and 1-Ethyl-3-Methylimidazolium Chloride

“…Much greater decrystallization occurred when using [PMIM] [Cl], which proves that this ionic liquid hydrolysis was effective, caused degradation of crystal regions, and thus increased the content of amorphous phase. This is in line with the work of Li et al [42], where the hydrolysis process is caused by the breaking of hydrogen bonds present in cellulose macromolecules, which as a consequence leads to shortening of polymer chains. Therefore, our observations regarding changes in the intensity of the diffraction maximum clearly indicate a different course of the cellulose hydrolysis process depending on the type of the cation.…”

On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide: a frustrated solvent

“…The addition of water or alcohol relaxes the frustration by allowing the formation of more hydrogen bonds to acetate. The need for a system to be frustrated to be a good cellulose solvent probably applies generally to IL solvents, for instance, a similar concepts has been applied to explain the difference in cellulose-dissolving ability of EmimCl and BmimCl by (Li et al 2015), and also to amine oxides like N-Methylmorpholine-N-oxide (NMMO) (Fink et al 2001). However, in aqueous systems, where abundant opportunity generally exists to form both acceptor and donor hydrogen bonds, frustrated conditions can only be attained for extremely high solute concentrations, such as in molten salt hydrates (Heinze and Koschella 2005).…”

Alkaline Sulfite Anthraquinone and Methanol (ASAM) Pulping Process of Tropical Bamboo (Gigantochloa scortechinii)

“…The cellulose content of G. scortechinii is in the range of both soft and hardwood, 40-52% and 38-56%, respectively [23]. The cellulose molecule has numerous hydroxyl groups, which have a strong tendency toward hydrogen bonding with hydroxyl of adjacent molecules [24]. This tendency in connection with the molecular structure is responsible for increasing fiber-to-fiber bonding in final paper [25,26].…”