Temperature spinning bath

An example of the first type is the use of low-acid, low-salt, and low-temperature spin-baths, which slow down the cellulose regeneration sufficiently to yield HWM polynosic rayon [190]. Another example is the Lilienfeld process for which the viscose, made from unaged alkali cellulose with excess carbon disulfide and only a short ripening, is spun into a cold spin-bath containing 50-85% of sulfuric acid. This is a case of stabilizing the xanthic acid. Rayon produced in this way has tenacities greater than 5 g/den. 

There are great opportunities to improve this property during the development stage of the discussed method. It is well known that several parameters including spin additives, coagulation time and temperature, spin bath chemicals, spinneret type, jet draw, finishing and stretch have significant effect on the fibre properties. These parameters have not been developed sufficiently yet. 

Process conditions that favor chemical crimp formation are similar to those used for improved tenacity staple (2inc/modifier route). However, spin bath temperature should be as high as possible (ca 60°C) and the spin-bath acid as low as possible (ca 7%). Attempts have been made to overcome some of the leanness of high strength rayons by increasing the crimp levels. ITT Rayonier developed the Prim a crimped HWM fiber (36) and made the process available to their customers. Avtex developed Avdl 111. Neither remain in production. 

The Courtaulds semicommercial production system is iUustrated in Figure 8. Dissolving-grade woodpulp is mixed into a paste with NMMO and passes through a high temperature dissolving unit to yield a clear viscous solution. This is filtered and spun into dilute NMMO whereupon the ceUulose fibers precipitate. These are washed and dried, and finally baled as staple or tow products as required by the market. The spin bath and wash Uquors are passed to solvent recovery systems which concentrate the NMMO to the level required for reuse in dissolution. 

Before reviewing existing examples, a very brief explanation on the mechanisms of decoherence for molecular spin qubits is necessary more details are available elsewhere [67]. Broadly speaking, the three decoherence sources for these systems are spin bath decoherence, oscillator bath decoherence and pairwise dipolar decoherence, and can be regulated by a combination of temperature, magnetic field and chemical design of the system [70]. The spin bath mainly consists of nuclear spins, but in general it also includes any localized excitations that can couple to the... 

For any reservoir in equilibrium the fluctuation-dissipation theorem provides the relation between the symmetrized and antisymmetrized correlators of the noise Sx(x) = Ax(x) coth(w/2T). Yet, the temperature dependence of Sx and Ax may vary depending on the type of the environment. For an oscillator bath, Ax (also called the spectral density Jx(x)) is temperature-independent, so that Sx(x) = Jx(x)coth(x/2T). On the other hand, for a spin bath Sx is temperature-independent and is related to the spins density of states, while Ax([Pg.14]

Such obvious benefits have stimulated solid-state MAS experiments at cryogenic temperatures in several research laboratories. In the most successful and reproducible case, a sealed sample with a liquid-nitrogen temperature spinning module was cooled in a helium bath, but rotation speeds did not exceed 2 kHz at 40 K and 1 kHz at 5 K [ 15]. This is a serious limitation for practical applications. 

Boil whole cell lysate place screw cap tube containing the thawed lysate sample in a boiling water bath or heat block at 100 °C for 5 min. Remove tubes from heat and allow tubes to cool to room temperature. Spin briefly in a microcentrifuge. 

Capone [219] has summarized more recent analysis of the diffusion behavior, and an example is the work by Baojin et al. [249]. The rate of diffusion is modeled from cylindrical coordinates again based on Pick s law. The composition of actual filaments from the spin bath was analyzed, and the coagulant was a DMP water system. Correlations are presented for diffusion coefficients and flux ratios as functions of jet stretch, polymer solution concentration, and coagulation temperature. The flux ratios, they reported, are similar to those reported in Paul s data, 20 years earlier. The diffusion coefficients are in the same range of 4-10 X lO cm /s that Paul found for DMAC-H2O systems. 

The structure of the fiber formed in the spin bath strongly influences the tensile properties of the final product. Knudsen [268] has demonstrated that the influence of the coagulation bath variables on the fiber tensile properties can be rationalized in terms of the uncollapsed fiber structure. As the spin-bath temperature is lowered and a denser and finer structure is... 

The dimensions of the fibrils and microvoids seen in the uncollapsed drawn fiber can be traced back to the structure of the freshly coagulated fiber. Knudsen [268] has shown that the reduction of the spin-bath temperature gives a denser and finer structure in both the first roll and drawn uncollapsed fiber, and furthermore, the tensile properties are improved. In Figure 12.32, the breaking tenacity and elongation are shown as a function of the draw ratio for different spin-bath temperatures. The lower spin-bath temperature produces a stronger and stiffer fiber. The lateral properties of the finished fiber are also improved by having the denser structure. The number of cycles-to-fail in a multifilament flex-abrasion test increases by a factor of 2-3 x when the spin-bath temperature is lowered from 55 to 0°C. This is attributed to an increase in the number of lateral interconnections between fibrils in the drawn fiber as the bath temperature is reduced. 

FIGURE 12.32 Dependence of fiber-breaking tenacity (top) and elongation (bottom) on orientation stretch ratio for different spin-bath temperatures. (From Knudsen, J.P., Text. Res. J. 33, 13, 1963.)... 

At a fixed distance from the spinneret, F(tot) is observed to increase with the jet stretch. (Recall that the jet stretch is the ratio of the speed at which the fiber leaves the spin bath to the theoretical speed of the dope within the spinneret capillary.) Furthermore, at constant jet stretch F(tot) will also increase as the distance from the spinneret is increased. Extrapolation to x = 0 gives /(rheo). In Figure 12.34, F(rheo) is plotted against the jet stretch for different coagulation bath conditions. It is seen that F(rheo) increases as the temperature is decreased from 40 to 0°C, and also as the bath concentration is decreased from 20 to 10%. The change in area of the filament as a function of the distance from the spinneret is A(x), and it can be measured by photographic determination of the filament diameter. 

FIGURE 12.34 Rheological force versus jet stretch at different spin-bath conditions. Spinneret diameter was 0.0127 cm (5 mils) and the plug flow velocity within the spinneret was 16.62cm/s. The concentration of sodium thiocyanate (NaSCN) in the bath and the bath temperature are given. (From Han, C.D. and Segal, L., /. Afip/. Polym. Sci. 14, 2973, 1970.)... 

Fig. 5. The spin-bath relaxation rates for Ce in LaMN, fitted to an Orbach process, 2.7 X 10 exp( —34/D, combined with R cotanh (ho)/2kT) at lower temperatures, where the lower rate for the higher concentration shows that it is limited by the phonon-bottleneck between spins and bath. (After Ruby et al. 1962.)...

The dope is pumped with a gear pump, at the required temperature (25 120°Q, through a spinneret with a multiplicity of holes, a total of 50-500,000 depending on the application and usually arranged in segments to improve the distribution of the spin bath (0 50°Q across the jet face. The jet is made from a material (e.g., 70 Au, 29.5 Pt, 0.5Rh) that will withstand the chemical environment and the holes (0.05-0.25 mm diameter) with a conical inlet and cylindrical capillary outlet formed by laser drilling. Cleanliness of the jet is most important, since blocked holes will introduce poor cosmetics. 

The sulfonate concentration in the microemulsion was determined from the equilibrated microemulsion phase volume and the known weight of sulfonate in the system the assumption that the microemulsion phase contained all of the sulfonate was justified for all microemulsions. The volume fractions of oil and brine in the microemulsion were determined from the excess volumes of oil and brine, respectively. The microemulsion density and index of refraction needed to calculate the specific refraction (Eq. (1)) were measured on a Mettler-Paar DMA 40 digital density meter with accuracy of 0.0001 g/cm and a Zeiss Abbe refractometer ( 0.0001), respectively the temperature was controlled with an Exacal 100 and Endocal 150 constant temperature circulator-baths connected in series. Interfacial tensions between the microemulsion and equilibrated excess phases were measured on a University of Texas Spinning Drop Tensiometer or a Spinning Drop Tensiometer from S S Instrument Mfg. measurements were carried out until equilibrium values were obtained as indicated by constant readings over a period of at least 1 hour. 

Finally, the spin thermodynamics picture assumes that the inverse temperature in the abundant spin bath is the same at any given point in time. That assumption is valid as long as these spins are strongly connected, i.e., as long as spin diffusion happens sufficiently fast. For protons, that is often the case at low/intermediate MAS frequencies. 

The basic chemistry of fiber formation is however independent of the hardware. Spin-bath liquors are mixtures of sulfuric acid (5-15%), zinc sulfate (0.05-7%), and sodium sulfate (10-28%) controlled at temperatures ranging from... 

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