Studies On Regenerated Cellulose Fibers Using Ionic Liquids As Solvents

Ionic liquids are regarded as "green solvents" which have wide potential applications in many fields.In recent years,the researches about dissolution and regeneration of cellulose in ionic liquids,especially in imidazole-based ionic liquids, have attracted much attention.However,so far the researches on rheological properties and spinnability of the cellulose/ionic liquid solutions as well as the structure and properties of regenerated fibers are still at the preliminary stage.In this thesis,two kinds of imidazole-based ionic liquids,the 1-butyl-3-methylimidazolium chloride([BMIM]C1) and the 1-ethyl-3-methylimidazolium acetate([EMIM]Ac),were used as solvents of cellulose.The solubility of cellulose in these two ionic liquids and rheological behavior and spinnability of resultant dopes were investigated.And the regenerated cellulose fibers were prepared by a dry-wet spinning method.Moreover,the effects of the kind of ionic liquid,spinning condition and dissolving process on structures and properties of the resultant fibers were also investigated.This work is expected to give scientific basis for commercialized production of regenerated cellulose fibers using ionic liquids as solvents.In this thesis,the solubility of cellulose in[BMIM]C1 and[EMIM]Ac was investigated by using a polarizing microscope with heating stage.The results showed that cellulose could be dissolved directly in both ionic liquids under certain condition. The dissolution temperature for cellulose was lower and its dissolution rate was higher in[EMIM]Ac than in[BMIM]C1.In addition,the degree of polymerization for cellulose pulp had more important effect on its solubility in ionic liquids than a -cellulose content.Moreover,the initial water content of ionic liquid also had a significant effect on dissolution of cellulose.Although the aqueous ionic liquid resulted in poor solubility of cellulose,it accelerated cellulose to be swollen well.In this thesis,the static and dynamic rheological behaviors of cellulose/ionic liquid solutions were further studied by using a cone-plate rheometer.It was found that both cellulose/[EMIM]Ac and cellulose/[BMIM]Cl solutions were the typical shear-thinning fluids.And the former had a lower apparent viscosity than the latter under the same condition,which means the cellulose/[EMIM]Ac solution could be spun at a lower temperature.Moreover,the rheological behaviors of the solutions were affected by not only the pulp properties,cellulose concentration and temperature but also the dissolving process of cellulose.The apparent viscosity of the solution prepared by an indirect dissolving process in which aqueous ionic liquid swelled cellulose first and then dissolved cellulose by removing the water,was lower than that of solution prepared by a direct dissolving process of cellulose using pure ionic liquid as solvent.The results from dynamic rheological analysis further showed that cellulose could be fully dissolved in ionic liquid by the indirect dissolving process and the resultant solution had better homogeneity.Based on these studies,two kinds of generated cellulose fibers were prepared by a dry-wet spinning method and using[BMIM]Cl and[EMIM]Ac as solvent, respectively.GPC results showed that during the dissolution and spinning process of cellulose,its degradation was greater in[BMIM]Cl than in[EMIM]Ac.The results from WAXD and SEM etc.showed that both fibers had smooth surface,round cross section and compact structure.Compared with the cellulose fiber from[EMIM]Ac system,the fiber from[BMIM]Cl system had higher crystallinity and orientation at the same draw ratio so that it had better mechanical properties.With the increase of cellulose concentration and draw ratio,the mechanical properties of regenerated cellulose fiber were improved.In addition,the dissolving process of cellulose also had great influence on the spinnability of dope and the mechanical properties of resultant fiber.The dope prepared by the indirect dissolving process of cellulose had a better spinnability and the mechanical properties of resultant fiber were improved. Moreover,it was found both generated cellulose fibers(using[EMIM]Ac and [BMIM]Cl as solvent,respectively) showed obvious fibrillation characteristic.