Study on ionic liquid/cellulose/coagulator phase diagram and its application in green spinning process

In this work, the cellulose phase separation behavior was investigated by using ionic liquids (ILs) as novel solvents to acquire a green process for cellulose fiber spinning. The cloud point titration method combined with the turbidity correlation equation was used to obtain the ternary diagram of IL/cellulose/coagulator throughout the whole compositional range. The effects of the type of ILs, the cellulose materials, the kind of coagulators and the regeneration temperatures for cellulose fiber manufacturing process on the phase separation behavior were studied systematically. It was found that the linearized cloud point (LCP) curve correlation fits to experimental data well and can be used to quantify the optimized coagulator, and among the studied cases, the system of [EMIM]DEP, cotton pulp and water with the regeneration temperature at 298.15 K is the best. Meanwhile, COSMO-RS was used to predict the interaction between solvent, cellulose and coagulator, and the comparison with the LCP correlation shows good agreement. The crystal structure of the regenerated cotton pulp was determined with XRD, and the result evidences that the crystal structure of the regenerated cellulose transforms from cellulose I to cellulose II. The crystallinity decreases from 96.0% (raw cotton pulp) to 85.6% after 24 h dissolution in [EMIM]DEP at 363.15 K, and it has a slight deviation from 24 h to 72 h, which illustrates that the spinning process can run continuously at 363.15 K when using [EMIM]DEP as the solvent. (C) 2019 Published by Elsevier B.V.