Ammonia/ammonium thiocyanate-cellulose system: Dissolution, viscoelastic behavior and fiber formation

The formation of high concentration and gel-free cellulose/ammonia/ammonium thiocyanate solutions with high molecular weight cellulose provided an excellent potential for forming cellulosic fibers with high mechanical properties. The range of cellulose concentrations included both the isotropic and anisotropic phases. The solvent dissolves cellulose in a wide concentration range quickly and with ease. The presence of water up to 15% of cellulose weight in the solvent did not affect the solvent effectiveness. Studies on the flow rate behavior of cellulose solutions prepared from either undried, containing 7% bound water, or pre-dried cellulose pulp revealed similar behavior.; The viscoelastic behavior of the cellulose solutions revealed the expected viscosity dependence on concentration. The zero-shear viscosity did not show the viscosity drop with concentration which can occur when the phase transition from isotropic to anisotropic is crossed. This viscosity dependence on concentration is observed only in the non-linear, high shear rate, viscoelastic region. The interesting rheological phase diagram is instructive in locating the solution concentration which allows one to spin cellulose solutions exhibiting the anisotropic phase.; The spinning of cellulose solutions showed that fibers with high mechanical properties were obtained from solutions possessing the anisotropic phase. Investigations on the method of washing the cellulose fiber exposed the effect of processing on the fiber properties. Fiber with approximately 4.65 g/den. tenacity and 212 g/den. initial modulus was obtained from anisotropic solution of 12% (w/w) cellulose concentration. This high mechanical property fiber is better than that of the commercially available solvent spun cellulose fiber, Tencel{dollar}sp{lcub}rm TM{rcub}.{dollar}; X-ray diffraction analysis revealed the highly crystalline nature of the cellulose fiber. The structural investigations by WAXS and solid-state CP/MAS {dollar}sp{lcub}13{rcub}{dollar}C NMR also showed that the cellulose fiber possessed the cellulose III polymorph conformation.; The ammonia/ammonium thiocyanate solvent has demonstrated its effectiveness in dissolving cellulose with high molecular weight to prepare solutions of high concentration. The ease and speed as well as its versatility in dissolving cellulose and the formation of fibers with high mechanical properties has demonstrated its potential commercial importance in replacing the century-old proven but environmentally destructive viscose process.