The crystallization and melting behavior of the system N‐methylmorpholine‐N‐oxide (MMNO)–H2O–cellulose has been studied by differential scanning calorimetry, optical and electron microscopy, and x‐ray scattering. The phase diagram of the MMNO–H2O solvent system is reported up to a water content of 28% w/w. MMNO forms two crystalline hydrates, namely a monohydrate (13,3% w/w H2O) and a hydrate comprising five molecules of crystal water per two MMNO molecules (28% w/w H2O), which melts at 78°C and 39°C, respectively. The melting points of the various diluent crystals are strongly depressed in the presence of cellulose. For example, the solvent liquidus curve in the quasibinary system MMNO.1H2O–cellulose can be described very well using the simple Flory–Huggins expression with an interaction parameter χ = −3. Finally, the MMNO‐rich part of the melting point/composition diagram of the quasiternary MMNO–H2O–cellulose system is constructed and discussed.

SynopsisCellulose mesophases were obtained by preparing concentrated solutions of cellulose (20-5570) in a mixture of N-methyl-morpholine N-oxide (MMNO) and water. The anisotropy depends on four interconnected parameters: the temperature of the solution which, in general, must be lower than 90°C; the concentration of cellulose which must exceed 20%; a water content such that the mole ratio water/anhydrous MMNO is smaller than unity; and the degree of polymerization of the dissolved cellulose. The anisotropic cellulose solutions can readily be oriented during extrusion or casting thus giving fibers or films which upon regeneration exhibit high orientation.

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SYNOPSISThe influence of a n air gap on the formation of a filament spun from a solution of cellulose in N-methylmorpholine N-oxide was studied. A number of parameters were investigated, principally, air-gap length, temperature, and humidity and the water content in the polymer solution. Their effect on the draw-down profile and orientation of the filament in the air gap was determined and compared to the structure and properties of the resulting fibers. It is shown that all these parameters have a strong influence on the structure formation process. Depending on the combination of parameters used, the phenomenon of draw resonance may or may not be observed. The results indicate that the cooling of the filament is driven by two simultaneous processes. Modifying the parameters studied also causes significant changes to the resulting fiber properties, but the fiber structures, measured by birefringence and wide-angle X-ray diffraction, appear almost identical. 0 1996 John Wiley & Sons, Inc. I NTRO DUCT10 NIn previous publications,ls2 we showed how the structure of a Lyocell fiber is built up during the spinning process and how physical parameters such as the spinning speed and the draw ratio affect this structure. We were able to verify that the predicted filament profile in the air gap fits well with measurements made in our laboratory, which show that the profile is unaffected by the draw ratio. We found that the draw length was controlled by the volumetric flow rate Q of the cellulose solution. The birefringence in the air gap (which is a measure of orientation) was measured and found to be proportional to the stress, except for the narrowest filament, for which some chain slippage was indicated. In the coagulation bath, the precipitation of the cellulose was diffusion-driven. The birefringence of the dry fiber depended only slightly on the prebath birefringence, except for highly unoriented fibers. We showed that a highly fibrillar structure is obtained, along with good mechanical properties, above a certain draw ratio. This limit was as low as five with a 100 pm spinneret. Other work has been done in this field. Dub6 and Blackwel13 studied the effect of precipitation conditions, solution composition, and drying conditions on the structure of the fibers. Navard and Haudin4 looked mainly at the effect of draw ratio (DR), showing the presence of draw resonance above a DR of 55. Quenin5 looked a t various parameters such as the type of amine oxide used as a solvent. The patent literature6-8 covers the fact that an air gap must be used in the process. Other work has been done by Taeger et al.' and Simon." None of this work has looked in detail a t how the air gap affects the formation of the fiber. The air gap is an important part of the process because it allows the drawing of the fiber to the desired linear density (dtex) and the orientation of the polymer to impart it with good mechanical properties, which makes poststretching unnecessary. It also allows the simultaneous use of a spinneret above 90°C and a coagu...