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An investigation of the diffusion competition between solvent and nonsolvent in a coagulation bath is presented for the formation of a new cellulosic fiber by wet‐spinning. The system consisted of the spinnable cellulose solution with a mixture of liquid ammonia/ammonia thiocynate as the solvent and low‐molecular‐weight alcohols as the nonsolvents. The diffusion competition between solvent and nonsolvent was quantitatively characterized in terms of their mass transfer rate differences. The measurements of this rate difference were performed on the model filament shaped from gelled cellulose solutions. Results revealed that an increase in molecular size of coagulant, bath temperature, and coagulant concentration in the bath enhanced preferential diffusion of solvent from cellulose solution. Fiber spinning experiments showed that a higher value of the initial modulus of the fiber was attained with a coagulation condition providing a lower value of mass transfer rate difference. The importance of mass transfer rate difference was also shown in the influence of the fiber cross‐sectional shapes.

An extensive study of the coagulation of cellulose from cellulose/ammonia/ammonium thiocyanate solutions is presented. The effect of major variables upon the coagulation process for cellulose solutions is reported. Microscopic observations of the moving boundary associated with the coagulation were performed on gelled cellulose solutions to determine the coagulation rate as a function of molecular volumes of coagulant, bath temperatures, bath compositions, and cellulose concentrations. The data were analyzed by means of a one‐dimensional linear diffusion model based on Fick's law, thereby depicting the mechanism of the coagulation process, and obtaining the diffusion coefficients of mobile components involved in the coagulation.

SYNOPSISFiber melt spinning of poly( ethylene terephthalate) (PET) was studied via modification of threadline dynamics. Several techniques were implemented in the high-speed spinning process for the judicious control of threadline dynamics. This included a thermal conditioning zone (TCZ) for controlling the threadline temperature profile and a hydraulic drag bath ( HDB ) for controlling the threadline spinning stress. Through controlled threadline dynamics, key factors affecting the structure development-namely, temperature, tensile stress, and crystallization time-were manipulated to favor formation of a highly oriented and transversely uniform structure in the spun fibers. This carries the implication that optimum or near-optimum processing conditions are being applied during the structure development period. More specifically, tensile stress in the threadline, independent of temperature, is substantially increased to many orders higher than that ordinarily attained in the normal high-speed spinning process. Concurrently, the temperature crucial to the structure development is being independently optimized and its duration extended to attain a highly oriented structural order. Properties of the spun fibers were found to be correlated with the threadline parameters including cooling profile, tension profile, and strain rate. PET fibers spun via the one-step process with the introduction of the TCZ and HDB possess superior mechanical performance. Structural characterization suggests that the spun fibers have a high amorphous orientation factor and a uniform radial structure distribution. Further on-line studies indicate that structure development in the threadline is completely different from that of the traditional high-speed spinning process. The attenuation profile of the threadline is observed to be dependent on TCZ temperature, residence time in the HDB, temperature of the HDB, and take-up speed. It is believed that for the melt spinning process with the 'TCZ and the HDB, the threadline dynamics is changed from one controlled by inertia and air drag forces to one controlled by the imposed hydraulic drag.

Ammonia/ammonium thiocyanate (NH3/NH4SCN) is an excellent swelling agent and solvent for cellulose, even at a high degree of polymerization. Because polymorphic conversion in cellulose has been a long‐standing, perplexing, troublesome problem, we have undertaken to study that mechanism. Solid state CP/MAS 13C‐NMR and X‐ray analysis proved to be very useful analytical techniques for the task. It appears that during temperature cycling, specific cellulosic inter‐ and intramolecular hydrogen‐bonds are broken as polymorphic conversion proceeds sequentially from the polymorph I to III, and finally at total solvation to amorphous. This proceeds correspondingly via transformation of the polymorph conformations of CH2OH from trans‐gauche, “tg,” to gauche‐trans, “gt,” to gauche‐gauche, “gg.” © 1994 John Wiley & Sons, Inc.

The hydrazine/thiocyanate system was found to be an excellent solvent for cellulose. The solubility and solution properties were investigated. Even at room temperature, the combinations of hydrazine and lithium, sodium, and potassium thiocyanate had high dissolution power for cellulose, up to an 18% (w/w) maximum, unrelated to the polymorph, whereas a combination with ammonium thiocyanate exhibited a solubility difference among celluloses I, II, and III. The effect of the temperature cycling of the system for the rapid dissolution of cellulose was investigated thermodynamically. In these systems, a high concentration of salts was necessary to effect the cellulose dissolution; this suggested that an undissociated salt-solvent complex played an important role in the cellulose dissolution as implied by electroconductivity measurements of the hydrazine/salt system. Gel and liquid-crystal formation was observed in all systems above 4 and 6% (w/w) cellulose concentrations, respectively. The values of both critical concentrations were quite similar to those observed in the ammonia/ammonium thiocyanate system studied earlier in our laboratories. The gelation temperature was between approximately 10 and 50°C, depending on the salt and cellulose concentration. The dependence of the cellulose solubility on the degree of polymerization was also examined. It is suggested that these solvent systems have great potential for the fiber and film formation of cellulose.

ABSTRACT:The ethylenediamine/thiocyanate salt system was found to be a new solvent for cellulose. The solubility, dissolution behavior, solution properties, and cellulose recovered from the solutions were investigated. The dissolution took place at room temperature, and the maximum solubility achieved was 16 % (w/w) for cellulose of DP210 in the ethylenediamine/sodium thiocyanate 54/46 (w/w). The dependence of cellulose solubility on DP is also described. Tracing the dissolution behavior of the cellulose by CP/MAS 13 C NMR measurements revealed the polymorphic conversion of cellulose I to III to amorphous structure during the dissolution process. The cellulose dissolved was stable for 30 days storage at room temperature. Microscopic observations and steady-shear viscosity measurements of the solutions indicated mesophase formation of cellulose in the ethylenediamine/sodium thiocyanate system. This anisotrpoic phase appeared from ca. 10 % (w/w) cellulose with DP210 and greatly depended on the cellulose concentrations. Coagulation studies disclosed that cellulose II and amorphous cellulose were recovered from the cellulose/ethylenediamine/thiocyanate salt solutions when water and alcohol were used as a coagulant, respectively. It was suggested that this solvent system has high potential for cellulosic fiber and film formations.KEY WORDS Cellulose / Cellulose Solvent / Cellulose Solution / Amine / Thiocyanate / Dissolution Mechanism / Regenerated Cellulose / Cellulose is a linear and high molecular weight polymer as well as a natural, renewable, and biodegradable material. However, due to its considerable inter-and intramolecular hydrogen bonds, cellulose neither melts nor dissolves readily in common solvents. The complicated crystalline and amorphous morphology has also been preventing cellulose from being exploited to its fullest potential. Any process which simplifies or hastens the dissolution of cellulose represents a significant step forward in the development of cellulose as a viable, ecologically favorable polymer source. Furthermore, the ability of cellulose and cellulose derivatives to form mesophase in certain solvents has resulted in attempts to develop high-performance cellulosic fibers and membrane. At present, there are a few solvents that can directly dissolve cellulose without heavy metal complexation and any chemical derivatization, which are lithium chloride/dimethyl acetamide (LiCl/DMAc), 3 N-methylmorpholine-N-oxide/water (NMMO/H 2 O), 4 calcium thiocyanate/water (Ca(SCN) 2 /H 2 O), 5 etc. Quite recently, ionic liquids containing 1-butyl-3-methylimidazolium cations were discovered to dissolve high M w pulp (DP % 1000) with 10 % (w/w) at elevated temperatures. 6 However, almost known solvents still have some undesirable points, for example, chemical safety, environmental concern, degradation of cellulose, requirements of high temperatures and/or pretreatment of cellulose, poor mechanical properties of the cellulose recovered, and high cost for commercial use.We have been studied new solvent for ...