Light-scattering studies on solutions of cellulose in the ammonia/ammonium thiocyanate solvent system. I. Classical light-scattering

This article reports the use of classical light scattering to study cellulose in the NH3/NH4SCN solvent system. Three solvent compositions were used, 27.01 73.0,25.5/ 74.5, and 24.51 75.5 weight ammonia/weight ammonium thiocyanate. The coefficient, (dn/dc)_υ, was determined by back calculating using the molecular weight determined by solution viscometry in the solvent system cupriethylenediamine and the classical light-scattering results. Second virial coefficients were found to be similar to those values measured for cellulose in the FeTNa and LiCl/DMAC solvent systems. The characteristic ratios were found to vary with solvent composition with the highest values being at a composition of 25.5/74.5 weight ammonia/ weight ammonium thiocyanate. Persistence lengths were also found to vary with solvent composition with the highest value being 264 × 10^?8 cm at solvent composition 25.5/74.5.     

Rheology and gelation of cellulose/ammonia/ammonium thiocyanate solutions

Liquid crystalline solutions of cellulose in an ammonia/ammonium thiocyanate solvent will form thermoreversible gels at temperatures below 30°C. These gels are of interest both for processing the cellulose/ammonia/ammonium thiocyanate system and because they have an unusual structure, containing neither crystalline nor covalently bonded crosslinks. Although these gels contain neither crystalline nor covalently bonded crosslinks, the dynamic rheological behavior of the system at the gel point was found to be the same as for gels with covalent or crystalline crosslinks with a loss tangent, tan δ, independent of frequency. The kinetics of the gelation process was monitored via dynamic elastic modulus, G′. All samples revealed an exponential increase in G′ with time during gelation, very different from that observed in covalently bonded or crystalline crosslinked systems. Measurements of the loss tangent enabled precise determination of the gelation time for these systems as a function of cellulose concentration and temperature. We found the gel time to be inversely related to cellulose concentration and directly related to temperature. The strong dependence of gel time on these parameters offers a windows of spinnability that can be tailored for processing high modulus cellulose fibers. © 1996 John Wiley & Sons, Inc.     

Lyotropic mesophases of cellulose in the ammonia/ammonium thiocyanate solvent system: Phase relationships

Mesophase formation of the cellulose/NH₃/NH₄SCN system has been studied as a function of system composition at 25°C. Compositions for incipience of mesophase formation and for wholly anisotropic phase formation have been determined and relevant phase diagrams constructed. The biphasic gap narrowed when the solvent composition approached 75.5 weight percent NH₄SCN and as the cellulose concentration decreased. As solvent composition was changed, the minimum cellulose volume fraction for mesophase formation ranged between 0.02 to 0.045.     

Coagulation studies for cellulose in the ammonia/ammonium thiocyanate (NH3/NH4SCN) direct solvent system

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.     

Fiber formation via solution spinning of the cellulose/ammonia/ammonium thiocyanate system

Fiber formation via the cellulose/ammonia/ammonium thiocyanate system by wet spinning has been investigated. This report presents a characterization of the structure and tensile properties of fibers spun under various coagulation conditions. Microscopic observations showed that the molecular size of coagulant was the dominant factor governing the crosssectional shape of the fibers. Density, birefringence, and crystallinity data indicated that a higher cellulose concentration and lower coagulation temperature favored development of a fiber with a denser and more oriented structure. Under optimum conditions, a welldefined fibrillar structure was obtained. Fiber tensile property measurements suggested the existence of a linear relationship between the fiber breaking tenacity and the product of the square of the Hermans' orientation factor and the infrared crystallinity index.     

Lyotropic mesophase of cellulose in ammonia/ammonium thiocyanate solution

Solutions of cellulose in a mixture of 27:73 (w/w) of liquid ammonia and ammonium thiocyanate become liquid crystalline at room temperature above a certain critical concentration which depends on the degree of polymerization of the dissolved cellulose. The high optical rotations of the solution suggest that the cellulose mesophase is cholesteric in nature. In the two-phase region, the cellulose solutions exhibit negatively birefringent spherulites that possess both ringed and nonringed internal structures. The anisotropic solutions can be oriented by shear, indicating high potential for spinning them into useful fibers.     

The solubility of cellulose in liquid ammonia/ammonium thiocyanate solutions: Thermoreversible gelation and a preliminary report on fiber formation

The melting temperatures of thermoreversible gels formed from solutions of cellulose in liquid ammonia/ammonium thiocyanate mixtures were measured over a volume fraction range of .01–.004. Three samples of cellulose with M_w ranging from 1 × 10⁵ to 1.64 × 10⁵ were used. The findings show that the structural makeup of the gels is strongly reflected in their time-dependent behavior. The reciprocal of their melting temperature is a nearly linear function of the logarithm of the cellulose concentration. The relation between the logarithm of M_w and the reciprocal temperature of gel melting was also nearly linear. Exothermic heats of reaction ranging from 150 to 460 kcal/mol were calculated from the Ferry-Eldridge relationship (? ln C/?) = ΔH_x/R for the formation of cross-links, assuming that they result from a binary association of chains. It is inferred that the cross-linking loci in the gel were crystallites that consisted of glucose units. In addition, an initial study is reported of the fiber-forming potential of the liquid ammonia/ammonium thiocyanate system. Rudimentary fiber extrusion from a modified syringe was readily demonstrated. Operable coagulation systems involved proton-donating agents as well as methanol. Tenacities of these unstretched, as spun fibers, ranged as high as 0.89 g/d.     

Calculated phase diagrams for cellulose/ammonia/ammonium thiocyanate solutions in comparison to experimental results

Flory's lattice theory for rigid rod molecules and Kuhn chains is used to calculate phase diagrams for cellulose/ammonia/ammonium thiocyanate solutions. Persistence length values measured by light scattering and reported previously are used as rod length values. Variations in the phase diagram based on varying rod length/solvent composition and cellulose molecular weight are explored. Spinodal curves are calculated in a region of the phase diagram predicting phase separation between two anisotropic solutions. Finally, calculated phase diagrams are compared to published data for the system. Discrepancies between theory and data may be accounted for by soft interactions between cellulose molecules and solvent which are not incorporated into the lattice theory.     

The solubility of cellulose in liquid ammonia/salt solutions

The dissolution of cellulose in solutions of liquid ammonia and ammonium thiocyanate is discussed. Viscosity measurements on dilute solutions of cellulose in this solvent over a range of shear rates and shear stresses are reported. A four-bulb Ubbelohde suspended level viscometer was used for the measurements. Plots of log [η] versus log M gave Mark-Houwink coefficients of a = 0.95 and K = 6.686 × 10^?5 at 25°C for [η] as dl/g. The Bloomfield equation was used to calculate effective bond lengths (b) from limiting viscosity numbers of cellulose in solutions of ammonia/ammonium thiocyanate and Cuene, respectively. Results indicate that cellulose may have similar configurations in both solvents and also that the ammonia solutions are true cellulose solutions. Miscibility of the cell- ulose/ammonia/ammonium thiocyanate solutions with organic solvents, such as glycerol, is also reported. Further, a few interesting characteristics of the liquid ammonia/ammonium salt solutions, discussed briefly, are the convenient boiling point, the rheological behavior, and the relatively high concentration of cellulose obtainable.     

The solubility of cellulose in liquid ammonia/ammonium thiocyanate solution: The effect of composition and temperature on dissolution and solution properties

The dissolution process and some solution properties of cellulose in mixtures of liquid ammonia (NH₃) and ammonium thiocyanate (NH₄SCN) are discussed. The mole fraction ratio of NH₃, NH₄SCN, and H₂O which dissolve cellulose were determined. The effect of temperature on several solution properties was also examined. The temperature coefficient d In [n]/dT for the limiting viscosity number [n] has a value of ?1.58 × 10^?2 °C^?1. This is considered to be rather large but is, in fact, a common occurrence for almost all cellulose derivatives in solution. The values for the Huggins constant K′ showed no systematic trends with temperature. They did, however, suggest the presence of considerable association of the cellulose in solution. Miscibility results of adding the cellulose solutions to organic liquids are also reported.     

Effects of ammonia/ammonium thiocyanate on cotton fabric

The effect of ammonia/ammonium thiocyanate (NH₃/NH₄SCN) treatment of the swelling behavior, structural changes, and physical properties of cotton sheeting was compared with that of sodium hydroxide and liquid ammonia mercerization. Increased percent shrinkage, accessibility to a large dye molecule, dyestuff absorption, swelling with water, and water imbibition showed that NH₃/NH₄SCN had improved the accessibility of the cotton fabric. X-ray diffractograms showed the characteristic Cellulose I crystal lattice. X-ray diffraction and infrared absorption spectroscopy indicated that the crystallite size was unchanged and the swelling from the NH₃/NH₄SCN treatment occurred in the amorphous regions of the cellulose since the observed crystal structure was unchanged. Moisture regain determinations and barium hydroxide absorption suggested that some recrystallization of the cellulose may have occurred from the NH₃/NH₄SCN treatment. Fibers treated with NH₃/NH₄SCN showed a cross sectional shape similar to that of the origianl fibers but with reduced lumen area.     

Diffusion competition between solvent and nonsolvent during the coagulation process of cellulose / ammonia / ammonium thiocynate fiber spinning system

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.     

Quasielastic light-scattering studies of micellar sodium dodecyl sulfate solutions at the low concentration limit

Correlation functions of scattered light intensity of carefully purified sodium dodecyl sulfate (SDS) solutions were measured as a function of tenside concentration and NaCl concentration of the aqueous phase. The correlation functions were analyzed by taking into account the influence of the Coulomb interaction between the micelle (macroion) and small electrolyte ions on the diffusion coefficient. Values of the hydrodynamic radius, the aggregation number, and the effective surface charges were obtained. The aggregation number increases from N = 27 to N = 95 upon increasing the NaCl concentration from 0 to 0.05 mole per liter, while it remains constant when the salt concentration increases further up to 0.2 mole per liter. The effective charge of the micelles decreases with increasing NaCl content in the whole concentration region studied. These results could be interpreted qualitatively in terms of a model which relates the existence of an equilibrium size of the micelles to the balance between hydrophobic and Coulomb interactions. Our results lead to the conclusion that at least up to an NaCl concentration of 0.2 mole per liter the SDS-micelles exhibit an oblate spherical shape rather than a cylindrical form.     

Rheological measurements and light-scattering experiments of dilute solutions of high molecular polystyrene. Light-scattering of flowing polymer solutions

We describe the behavior of dilute polymer solutions by means of light-scattering under shear flow. Solution properties of polystyrene in benzene over a wide range of molecular weight has been studied to determine the coefficientsa andK of the Mark-Houwink relationship and to estimate the rheological conditions with regard to light-scattering experiments of flowing polymer solutions. The investigations were carried out to measure the shear-rate dependence of macromolecules in solution, e.g., to observe an orientation and changing of the mean-square radius of gyration.     

Rheological behavior of cellulose/silk fibroin blend solutions with ionic liquid as solvent

The rheological behavior of cellulose and silk fibroin blend in 1-butyl-3-methylimidazolium chloride was studied. The data from the rheological results was analyzed to understand the microstructure of the blend solutions. The viscosity and dynamic modulus of the blend solution decreased with increasing ratio of silk fibroin. While comparing the experimental results with the calculated data from the log-additivity rule, it is revealed that zero-shear viscosity, dynamic modulus show positive–negative deviations and a typical continuous–discrete type of morphology could be imaged. At lower shear rate, the change of phase morphology took place at the ratio of about 0.5 volume fraction of cellulose. However, the blend solution showed positive deviations for all cellulose/silk fibroin blend ratios at high shear rate, which indicates that the dispersion of cellulose and silk fibroin was improved under shear stress. The properties of cellulose/silk fibroin blends observed by Fourier transform infrared spectroscopy and scanning electron microcopy agreed with the result from rheology.     

High-resolution 13C NMR studies of cellulose and cellulose oligomers in ionic liquid solutions

High-resolution 13C NMR studies of cellulose and cellulose oligomers dissolved in the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) show that the beta-(1-->4)-linked glucose oligomers are disordered in this medium and have a conformational behavior which parallels the one observed in water, and thus, reveal that the polymer is disordered in IL solution as well.     

14N NMR studies of thallium nitrate solutions in liquid ammonia

¹⁴N chemical shifts and linewidths were determined for NO ₃ ^– and NH₃ in liquid ammonia solutions of thallium nitrate at concentrations between 0.07 and 10 M. The concentration dependences of the¹⁴NO ₃ ^– shift and linewidth are consistent with the presence of C_2v ion pairs at a 2:1 mole ratio of NH₃ to TINO₃ and C_3v ion pairs at mole ratios of 3:1 or higher. Previous studies had indicated the formation of ion pairs at low concentrations. The small value of the¹⁴NO ₃ ^– linewidth below 1 M suggests that these are contact ion pairs. Studies of the¹⁴NH₃ linewidth as a function of thallium salt concentration indicate slow solvent exchange at very high concentrations.¹⁴NH₃ exhibits a downfield shift upon incorporation into the solvation sphere of the Tl⁺NO ₃ ^– ion pair, in constrast to upfield shifts reported for complexation with transition metal cations.     

The coagulation of cellulose from anisotropic solutions in the NH3/NH4SCN solvent system

Coagulation of cellulose has been studied in cellulose/ammonia/ammonium thiocyanate anisotropic solutions. The effect of coagulation variables such as coagulant, bath temperature, and cellulose concentration on the coagulation process is reported. The coagulation rate was measured by microscopic observation of the moving boundary associated with coagulation. Results indicate that the coagulation rate increases with increasing cellulose concentration and bath temperature. Methanol has the highest coagulation power among the coagulants employed. Mass transfer rate difference and equilibrium swelling were also measured. The results on the mass transfer rate differences show that the mass transfer rate of NH₃/NH₄SCN is greater than those of the respective coagulants under all coagulation conditions. The equilibrium swelling decreases with increasing bath temperature and cellulose concentration.     

Studies on the solvent extraction of technetium from thiocyanate solutions in mineral acids

Technetium-99m, separated from fission molybdenum-99, has been studied as a component of liquid-liquid phase distribution equilibria. 5-(4-Pyridyl)nonane in a carrier diluent, benzene, has been used to study the distribution of the nuclide from thermodynamically suitable aqueous phases of electrolytes with and without sterically receptive thiocyanate ions. Efficient extraction of the metal can be accomplished in a variety of aqueous phase compositions. The separation factors with respect to molybdenum, under certain experimental conditions, are fairly high. The data have been utilized to effect clean separations of technetium from molybdenum.     

Morphological studies of liquid-crystalline cellulose derivatives. II. Hydroxypropyl cellulose films prepared from liquid-crystalline aqueous solutions

A morphological study of hydroxypropyl cellulose (HPC) was performed on solid films prepared by casting from a liquid-crystalline aqueous solution at rest or under shear. Electron microscopic observations reveal that many round particles composed of stacked disks are densely packed in the interior of a quiescently cast HPC film, while on the film surface formation of fibrous textures is also noted. Shear-deformed HPC films exhibit some interesting morphological features according to the shearing conditions. It is found by electron microscopy that the originally round particles become more and more elongated as shear stress increases. The resulting rodlike fibrillar entities are considerably aligned in the shear direction (SD), but form a banded structure with periodic discontinuities of molecular orientation distribution along the SD. A new mechanism of structural transformation is proposed in order to interpret these results.