Effect of alkyl chain length in anion on dissolution of cellulose in 1-butyl-3-methylimidazolium carboxylate ionic liquids

In recent years, 1-butyl-3-methylimidazolium carboxylate ionic liquids (ILs) have been reported to be powerful solvents for cellulose. However, little is known for the influence of the chain length in carboxylate anion on the solubility of cellulose. Therefore, in this work, we have synthesized 1-butyl-3-methylimidazolium carboxylate ILs including 1-butyl-3-methylimidazolium formate ([C4mim][HCOO]), acetate ([C4mim][CH3COO]), propionate ([C4mim][CH3CH2COO]) and butyrate ([C4mim][CH3(CH2)2COO]), in which the alkyl chain length in the carboxylate anion is being varied. Solubilities of cellulose in the ILs have been determined experimentally at 70 °C. The effect of the chain length in carboxylate anion on the solubility of cellulose has been estimated and investigated by 1H NMR. Meanwhile, the regenerated cellulose from the ILs were investigated by scanning electron micrograph (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. Such knowledge would enhance our understanding of the design of novel ILs for cellulose.