Temperature shear viscosity

Flow processes iaside the spinneret are governed by shear viscosity and shear rate. PET is a non-Newtonian elastic fluid. Spinning filament tension and molecular orientation depend on polymer temperature and viscosity, spinneret capillary diameter and length, spin speed, rate of filament cooling, inertia, and air drag (69,70). These variables combine to attenuate the fiber and orient and sometimes crystallize the molecular chains (71). 

The Rheometric Scientific RDA II dynamic analy2er is designed for characteri2ation of polymer melts and soHds in the form of rectangular bars. It makes computer-controUed measurements of dynamic shear viscosity, elastic modulus, loss modulus, tan 5, and linear thermal expansion coefficient over a temperature range of ambient to 600°C (—150°C optional) at frequencies 10 -500 rad/s. It is particularly useful for the characteri2ation of materials that experience considerable changes in properties because of thermal transitions or chemical reactions. 

In a fluid under stress, the ratio of the shear stress, r. to the rate of strain, y, is called the shear viscosity, rj, and is analogous to the modulus of a solid. In an ideal (Newtonian) fluid the viscosity is a material constant. However, for plastics the viscosity varies depending on the stress, strain rate, temperature etc. A typical relationship between shear stress and shear rate for a plastic is shown in Fig. 5.1. 

At low shear rates, aqueous solutions of polyacrylamide are pseudoplastic. With increasing shear rates and temperature the viscosity of the solutions decrease. At high shear rates during violent mixing and pumping operations the molecular weight of polyacrylamide decreases by destruction of macromolecules. 

Kalyan et al. [56] have also studied the effect of alpha-olefin comonomers on the rheological properties and processing of LLDPE. The characteristics of the resins are shown in Table 2. It is found that 1-octene-based LLDPE has the lowest shear viscosity as compared to 1-butene- and 1-hexene-based polymers (Fig. 9). Decrease in power consumption, pressure before the die, temperature in the die, and increase in output has also been found according to shear viscosities of the polymers during tubular film extrusion. 

Shear viscosities of the twin-screw blended materials were measured at 190°C and 290°C (Fig. 6), the same temperatures as the melt temperatures during processing 190°C for the composites and 290°C for the melt blends. 

The Lewis number, Le, is that of the deficient species (fuel or oxidant) in the mixture. In their analysis, Clavin and Williams used the simplifying approximation that the shear viscosity, the Lewis number, and the Prandtl numbers are all temperature-independent. They also showed that, at least for weak flame stretch and curvature, the change in local flame speed due to stretch and curvature is described by the same Markstein number ... 

While electrical conductivity, diffusion coefficients, and shear viscosity are determined by weak perturbations of the fundamental diffu-sional motions, thermal conductivity is dominated by the vibrational motions of ions. Heat can be transmitted through material substances without any bulk flow or long-range diffusion occurring, simply by the exchange of momentum via collisions of particles. It is for this reason that in liquids in which the rate constants for viscous flow and electrical conductivity are highly temperature dependent, the thermal conductivity remains essentially the same at lower as at much higher temperatures and more fluid conditions. 

Shear viscosity is a measure of the ahihty of one layer of molecules to move over an adjacent layer. Bulk viscosity will be mentioned in Section V.2. Since viscosity usually refers to shear viscosity, the term will he used in this way unless otherwise stated. Recommended techniques for measuring the viscosity of high-temperature melt are given below. Experimental data are available from the database mentioned in Section 1.2. Data on viscosities of slags (7 single component systems, 35 two-component... 

The bulk viscosities of molten alkali nitrates measured by Ejima s group 140 are shown in Fig. 27, where the bulk viscosity decreases with increasing temperature. The ratios of /r are approximately constant over the temperature range investigated. This suggests that the activation energies of the bulk viscosity and the shear viscosity are much the same. 

It is important from a practical viewpoint to predict the shear viscosity of mixtures from those of pure melts. For alkali nitrate melts, a linear dependence has been found between the reorientational line width obtained by Raman measurements and the ratio of temperature divided by shear viscosity.For NO3 ions, the depolarized Raman scattering from 1050cm" total stretching vibrational mode (Al) has a contribution to the line width L, which is caused by the reorientational relaxation time of the Csv axis of this ion. The Stokes-Einstein-Debye(SED) relation establishes a relation between the shear viscosity r of a melt and the relaxation time for the reorientation of a particle immersed in it ... 

The viscosity level in the range of the Newtonian viscosity r 0 of the flow curve can be determined on the basis of molecular models. For this, just a single point measurement in the zero-shear viscosity range is necessary, when applying the Mark-Houwink relationship. This zero-shear viscosity, q0, depends on the concentration and molar mass of the dissolved polymer for a given solvent, pressure, temperature, molar mass distribution Mw/Mn, i.e. 

The latter point is illustrated by the surface shear viscosities of the homochiral and heterochiral films at surface pressures below the monolayer stability limits. Table 7 gives the surface shear viscosities at surface pressures of 2.5 and 5 dyn cm -1 in the temperature range given in Fig. 19 (20-40°C). Neither enantiomeric nor racemic films flow under these conditions at the lower temperature extreme, while at 30°C the racemic system is the more fluid, Newtonian film. However, in the 35-40°C temperature range, the racemic and enantiomeric film systems are both Newtonian in flow, and have surface shear viscosities that are independent of stereochemistry. These results are not surprising when one considers that (i) when the monolayer stability limit is below the surface pressure at which shear viscosity is measured, the film system does not flow, or flows in a non-Newtonian manner (ii) when the monolayer stability limit is above the surface pressure... 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

A new polymer was developed by the polymer scientists in a company. A sample has been provided to the process development laboratory to determine the viscosity of the polymer as a function of shear rate and temperature. The instrument available is an old capillary rheometer. The piston has a diameter of 9.525 mm, and a series of capillaries that fit the rheometer barrel have a diameter of 2.54 mm and lengths of 25.4, 50.8, 76.2, and 101.6 mm. The rheometer temperature was set at 270 °C. Shear viscosity data are needed to estimate process performance. 

Table 3.7 Example Viscosity Data at Two Temperatures and Two Shear Rates. Data Shows the Effect of Temperature on Viscosity...

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