Ionic liquids as Green Solvents for Cellulose Chemistry

MSc (Chemistry ), North-West University, Mafikeng CampusCellulose is a polymer that lacks solubility in many conventional solvents and this limits its applications. Recently ionic liquids (ILs) have been reported to be good and green solvents for the cellulose processing. Therefore, the aim of this project was to provide the experimental perspective of the influence of the dimethyl formamide (DMF) on microcrystalline cellulose (MCC) dissolution process using ionic liquids (ILs) namely: 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]), 1-Butyl-3-methylpyridinium chloride ([BMPy][Cl]). The MCC dissolution process was carried out in three ionic liquids solvents namely: [BMIM][Cl], [AMIM][Cl] and [BMPy][Cl] as well as their co-solvents with (DMF). The dissolution process of ILs, and their co-solvent systems was carried out at temperature of 65 °C ± 5 °C at ambient pressure. After cellulose had been dissolved, it was then regenerated using deionized water. The regenerated cellulose fibers were characterized by various techniques: Fourier Transform Infrared Spectrometry (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Characterization results revealed that the regenerated cellulose previously dissolved in ILs [BMIM][Cl], [AMIM][Cl] and [BMPy][Cl] was similar to the regenerated cellulose previously dissolved in ILs with DMF: [BMIM][Cl]/DMF, [AMIM][Cl]/DMF and [BMPy][Cl]/DMF, respectively. Furthermore, these results were compared with the results of the pure cellulose (MCC). Properties of the regenerated cellulose were slightly different from those of the pure cellulose. The regenerated cellulose was mainly cellulose II and amorphous whereas pure cellulose was cellulose I, which showed that during regeneration process, the pure cellulose was unable to reconstruct back to its native state hence it precipitated as cellulose II having high amorphous region. Moreover, FTIR results for the regenerated cellulose showed that no new chemical bonds were formed which revealed that during the dissolution process there was no chemical reaction taking place. Using the obtained results of the regenerated cellulose fibres previously dissolved in ILs and their co-solvents, it was concluded that during the dissolution process DMF does not interact with cellulose however, it increases the ionic mobility of anion which lead to faster dissolution rate and it also increases ILs ability to dissolve more cellulose as shown in the theoretical studies [108- 119]. Thermophysical properties (density, ρ, sound velocity, u, and refractive index, nD,) measurements of cellulose mixtures at various molalities were made to confirm the dissolution process took place in the solvent system of [BMIM][Cl]/DMF or [AMIM][Cl]/DMF or [BMPy][Cl]/DMF. Thermophysical properties of cellulose with ILs was not conducted since those mixtures were not liquid at room temperature As molality increased density, ρ, sound velocity, u, and refractive index, nD, also increased which showed that cellulose were dissolved due to solvent-solute interaction.Master