Characterization of the regenerated cellulose films in ionic liquids and rheological properties of the solutions

Highlights: → The solubility can reach 13 wt% at 90 deg. C in ionic liquid of [bmim]Cl. → Additive N-methylimidazole can minimize DP loss of the regenerated films. → A mechanism of the dissolution of cellulose in [bmim]Cl was proposed. → The ionic liquid of [bmim]Cl could be recycled. - Abstract: Dissolution and regeneration of cotton pulp using ionic liquids as solvent was investigated. The physicochemical properties of the regenerated cellulose films have been characterized by scanning electron microscopy, X-ray diffractometer, infrared spectrometric analyzer, differential scanning calorimeter, and thermogravimetric analysis instrument. The rheological properties of cotton pulp dissolved in ionic liquids have been investigated by steady shear and oscillatory shear measurements. The influences of experimental parameters, such as the reaction temperature, additives on the solubility and degree of polymerization (DP) of regenerated cellulose were also studied. The results show that 1-butyl-3-methylimidazolium chloride ([bmim]Cl) was a good solvent to dissolve cotton pulp and the solubility can reach 13 wt% at 90 deg. C, but the DP remarkably decreased from 510 to 180 within 7 h. It was found that additive N-methylimidazole can effectively minimize DP loss of the regenerated cellulose, which can attribute to the fact that in the mixture of [bmim]Cl and NMI solution, the β-1,4-glycosidic bond of the cellulose chains cannot be broken because of the relative low concentration of Cl-. In the steady shear measurement, all the solutions show a shear thinning behavior at high shear rates. In addition, a mechanism of the dissolution of cellulose in [bmim]Cl was proposed.