Understanding the role of Dimethylformamide as co-solvents in the dissolution of cellulose in ionic liquids: Experimental and theoretical approach

Abstract Cellulose has been identified as the most abundant renewable material but however utilization of cellulose is still limited, it does not dissolve in most convectional solvents. This study focusses on cellulose dissolution using ionic liquids (ILs) namely: 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]) and 1-butyl-3-methylpyridinium chloride ([BMPy][Cl]) with N,N-dimethylformamide (DMF) co-solvent. The solubility of the cellulose was tested in pure ILs as well as in solution of ILs/DMF. Results showed that solubility of the cellulose in ILs greatly enhanced in the presence of DMF. The complete dissolution of cellulose in both the systems such as pure ILs and ILs/DMF was also evident by density (ρ), sound velocity (u) and refractive index (nD) measurements. Furthermore, COSMO-RS analysis was also performed in order to achieve a better understanding of the molecular interactions between the ILs and the co-solvent. In addition to the above theoretical chemistry tools, natural bond orbital (NBO), Fragment molecular orbital (FMO) and chemical reactivity analyses for cellulose molecule was investigated. Theoretical data obtained proved that cellulose molecule is more reactive than glucose. In addition, this study also deals with the regeneration of the cellulose from dissolved solution using deionized water. The regenerated cellulose was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. It was observed that the cellulose regenerated cellulose from both solvent systems hold excellent mechanical properties.