Deep eutectic solvents (DESs) for cellulose dissolution: a mini-review

Deep eutectic solvents (DESs), which are a novel class of sustainable designer solvents, have attracted considerable attentions in the field of cellulose chemistry. Due to their low cost and analogous physico-chemical properties to ionic liquids, DESs are expected to be alternative solvents for dissolving cellulose. However, at present, the solubility of cellulose in DESs is much lower than in most ionic liquids. In this mini-review, we briefly summarize the current state of knowledge about cellulose dissolution in DESs. By comparing with similar solvents, it was found that the components of current DESs are usually involved in hydrogen bond interaction making difficult their interaction with the hydrogen bond network of cellulose. Accordingly, we propose a strategy that the components which have good hydrogen bond accepting ability, such as Cl^-, OAc^-, HCOO^-, (MeO)₂PO₂^-, morpholine and imidazole, are promising choices to form DESs for cellulose dissolution. Ultrasound-assisted treatment and adding a surfactant are effective ways to promote cellulose solubility by enhancing the permeability of DESs.