Effects of coagulation conditions on structure and properties of cellulose-based fibers from aqueous NaOH solvent

Hydroxyethyl cellulose (HEC) fibers with low degree of substitution were prepared by wet spinning of solutions in 8 wt% NaOH solvent, and H2SO4/Na2SO4/ZnSO4 solution was chosen as coagulants. The influence of coagulation temperature and H2SO4 concentration on structure and mechanical properties of resultant HEC fibers was examined by synchrotron X-ray measurements, scanning electron microscope and tensile tests. The results were analyzed from the perspective of coagulation kinetics by determining coagulation rate and mass transfer rate difference. It is shown that the increase of either coagulation temperature or H2SO4 concentration would accelerate the diffusion and coagulation process. The lowest coagulation temperature of 20 °C or moderate H2SO4 concentration around 10-15 wt%, which provided a gentle solidification process, favored the development of regular crystal and oriented structure, uniform and dense inner structure as well as cross sections closer to circular, resulting in HEC fibers with better tensile properties.