Effect of pre-hydrolysis on the dissolution of hardwood pulp in double salt ionic liquid

Abstract

Abstract Ionic liquids (ILs) are potentially alternative solvents for cellulose dissolution. In this article, effect of hemicellulose in cellulose dissolution in ILs and the regeneration process were investigated. Hardwood pulps were produced by kraft (KP) and pre-hydrolysis kraft (PHKP) processes. The α-cellulose and residual pentosan contents were 95.6 % and 4.2 % in PHKP and 84.3 % and 9.9 % in KP, respectively. Both pulps were dissolved in 1-butyl-3-methylimidazolium chloride [C4mim]Cl, 1-butyl-3-methylimidazolium acetate [C4mim]CH3CO2 and their double salt (DSIL), [C4mim](CH3CO2)0.6Cl0.4 at 90 °C. It was observed that PHKP had slightly higher solubility in both ILs and DSIL. The dissolved pulps were regenerated by water and characterized by FTIR, TGA, X-ray diffraction, and viscosity. Regenerated pulp film formed smooth and homogenous surface. The viscosity of regenerated PHKP was higher than the original PHKP, which affected the strength of the produced cellulose film. As observed in FTIR, the regenerated cellulose showed a stronger absorption band at 1,647 cm−1 corresponding to the C–O stretching vibration of C–O–H. The crystalline structures of regenerated KP and PHKP from [C4mim](CH3CO2)0.6Cl0.4 changed to cellulose II form from the original cellulose I form.