Rheological models for gypsum plaster pastes

Shear stress and shear rate data obtained for gypsum plaster pastes were correlated by means of different rheological models. The pastes were prepared from a commercial calcium sulfate hemihydrate at various water/plaster ratios ranging from 100/150 to 100/190. The tests were performed at 25°C using a rotating coaxial cylinder viscosimeter. The measurements were accomplished by applying a step-wise decreasing shear rate sequence. Discrimination among the models was made: (1) on the basis of the fitting goodness; (2) by checking the physical meaning of the calculated parameters; (3) on the basis of the stability of the parameters and of their prediction capacity beyond the limits of the experimental data. In the light of above, the Casson model seemed to be most effective for application to gypsum plaster pastes. K Consistency - n Power-law index - N Number of experimental data - P Number of parameters - Shear rate (s^–1) - ₀ Viscosity (Pa · s) - _d Dispersing medium viscosity (Pa · s) - _p Plastic viscosity (Pa · s) - Viscosity at zero shear rate (Pa · s) - Viscosity at infinite shear rate (Pa · s) - [] Intrinsic viscosity - ² Variance - Shear stress (Pa) - ₀ Yield stress (Pa) - Solid volume fraction - _m Maximum solid volume fraction     

Rheological behavior of water-creosote and creosote-water emulsions

The effect of temperature on the steady-shear viscosity of two base emulsions (water-in-creosote (w/o) and creosote-in-water (o/w)) and a pigment emulsified creosote (PEC) was investigated. The PEC is a water-in-creosote emulsion which contains also a solid, micronised pigment, and is used industrially as a wood preservative. All three emulsions exhibited shear thinning characteristics at different temperatures. The viscosity-shear rate relationships follow a modified Quemada model. A temperature-superposition method using the reduced variables / and t _c was applied to yield a master plot for each of these emulsions at different temperatures. The effect of creosote concentration on the viscosity of four other o/w emulsions at different temperatures was also studied. The same reduced variables were able to produce a temperature-concentration superposition plot for all of the o/w emulsion results.The effective (average) radius of the globules (dispersed phase) was found to increase with increasing temperature for the base w/o and the PEC emulsion. The collision theory could be used to explain the increase in the droplet size. However, while little overall variation in globule size was observed for the o/w emulsions, microscopic observation indicated an increase in the proportion of large diameter droplets with temperature at the highest creosote concentration (60%). A creaming effect (phase concentration) was observed with these emulsions at higher temperatures, precluding an accurate estimate of droplet size based on collision theory.Seconded from Koppers Coal Tar Products, Newcastle, N.S.W., Australia.     

Rheological characterization of highly branched poly(ethyleneterephthalate)

Linear and highly branched poly(ethyleneterephthalate) samples were synthesized and characterized in terms of intrinsic viscosity, molecular weight and melt viscosity over a wide range of shear rates at several temperatures, in the range from 265° to 295 °C. Linear samples exhibited Newtonian behavior over a wide range of shear rates, while the branched ones became shear thinning at relatively low shear rates. Our experimental data, as well as data previously reported, were found to be described by a proposed correlation between the melt viscosity ratio and a branching index. Moreover, the activation energy for melt flow was found for the highly branched samples to be a little higher than that of the linear samples.     

Rheological properties of lightly crosslinked carboxy copolymers in aqueous solutions

The rheological properties of a series of lightly crosslinked carboxy copolymers in aqueous solutions have been evaluated in steady shear and dynamic oscillatory modes. Viscosity profiles and the behavior of storage modulus are related to the chemical composition of the copolymers and their crosslinking density. A maximum in viscosity and in storage modulus which depends on the type of crosslinking agent used is explained by a combination of a chain entanglement mechanism and a closely-packed spheres model. The recovery of viscosity and storage modulus after shearing is very fast and is related to the very fast rearrangement of the microgel structure as a function of time.     

Rheological properties of fresh cement pastes and clinker reactivity

This paper presents research results concerning the influence of clinker reactivity on rheological properties of cement pastes at early stages of hydration (lasting less than one hour). The research was carried out on clinkers synthesized in a laboratory, on non-alkaline cements and cements containing in-built alkalis (sodium, potassium) in the clinker phase.The clinker reactivity was estimated from the flow curves and stress changes in time occurring in clinker pastes while maintaining constant measurement parameters. It was found that the effectiveness of gypsum as a setting controller depends on clinker reactivity. Increased clinker reactivity is accompanied by a decreased consistency of a cement paste.The research results indicate that decreased reactivity of clinkers containing inbuilt alkalis is connected with decreased setting controlling effectiveness of added gypsum. This is manifested by a consistency increase of such system at early stages of hydration.     

Rheological characteristics of glass-fibre-filled polypropylene melts

The rheological properties of glass fibre-filled polypropylene melts have been investigated. A high pressure capillary rheometer has been used for the experimental study. The effect of shear rate, temperature, and fibre concentration on the melt viscosity and viscoelastic properties have been studied. An equation has been proposed to correlate the melt viscosity with shear rate, temperature and fibre content. A master curve relation on this basis has been brought out using the shift factora _T . a _T shift factor (=/ _r ) - A _i coefficients of the polynomical of eq. (1) (i = 0, 1, 2, ,n) - B constant in the AFE equation (eq. (2)) (Pa s) - B constant in eq. (3) - D extrudate diameter - d capillary diameter - activation energy at constant shear rate (kcal/mole) - E activation energy at constant shear stress (kcal/mole) - T melt temperature (K) - X fraction glass fibre by weight - shear rate (s^–1) - shear viscosity (Pa s) - normal stress coefficient (Pa s²) - ₁ – ₂ first normal-stress difference (Pa) - shear stress (Pa) - r at reference temperature     

Rheological material functions of polymer solutions using a generalized Maxwell model with slip functions Part I: Theory

A generalization of the Maxwell model for polymer systems is derived that replaces the velocity gradient in the Eulerian expression for the upper convected derivative by a tensorial kinematic function. Applying the principle of objectivity this tensorial function is reduced to two scalar slip functions. In shear flows, only one of the two occurs. Material functions are calculated in closed form, and asymptotic conditions are formulated that guarantee isotropic behaviour of the material in sudden strains.Presented at the second conference Recent Developments in Structured Continua, May 23–25, 1990, in Sherbrooke, Québec, Canada.     

Der elektroviskose Effekt als Folge elektrostatischer Kraft

Zusammenfassung Die Viskosität vieler Flüssigkeiten ändert sich als Folge elektrischer Felder. Die größten elektroviskosen Effekte findet man unter äußerem Feld bei Suspensionen aus dielektrischen Flüssigkeiten und feinen Festkörperteilchen.Die Flüssigkeiten zeigen ausgeprägtes Bingham-Verhalten. Solange die auf die Wand ausgeübte Scherspannung kleiner als die von der Feldstärke abhängige Haftspannung ist, verhalten sich die Materialien wie Festkörper. Man beobachtet, daß Elektroviskosität proportional zur Feldstärke im Quadrat und umgekehrt proportional zur Schergeschwindigkeit ist, und daß sich die Teilchen der Flüssigkeiten in Richtung der Feldstärke orientieren und faserige Strukturen bilden. In dieser Arbeit erklären wir diese Eigenschaften durch ein einfaches Modell. In diesem Modell resultiert die Scherkraftzunahme aus der elektrostatischen Kraft, die sich als Gradient der im Feld abgespeicherten Energie ergibt.The electroviscosity effect following electrostatic force

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Apparent viscosity of many fluids changes under an electric field. The largest effects are found with dispersions of fine particles in dielectric liquids subjected to an externally applied field. The large effect is apparently due to induced fibration when the particles align themselves as fibers in field direction. The dispersions exhibit Bingham-behavior, i.e., as long as the shear stress is smaller than the field-dependent yield stress, the material behaves as a solid, a behavior which can be made plausible as the electrodes are mechanically linked together by the fibers (Winslow 1949). In this paper arguments are put forward that the induced fibration is the consequence of electrostatic forces acting on the particles and pulling them into regions of higher field strength. The resulting configuration is an equilibrium configuration and it is postulated that even under shear load, the electric field tends to maintain this configuration such that only the particles close to the electrodes are sheared off, which then form a suspension near the electrode surfaces. A phenomenological theory based on the assumption that the fibers are columns of rectangular particles gives quantitative results for the electroviscosity and the yield stress which agree with experimental observations.

     

Rheological properties of service weathered road bitumens

A study was carried out of the rheological properties of service weathered bitumens and their properties were compared with road performance. Bitumen from 39 test sites was recovered from the uppermost layer of stone particles covering the road surfacing and tested under dynamic and transient loading. Dynamic testing was carried out under forced sinusoidal loading. Testing under transient loading was mainly with a viscosity test conducted at 45°C, but some creep testing in compression was conducted at 0°C. From the results of dynamic testing, master curves of modulus and loss angle were constructed, spanning over ten decades in loading frequency. The hyperbolic expressions of Dickinson and Witt successfully described the frequency dependence of bitumen modulus and loss angle. The Williams, Landel and Ferry (WLF) equation, with newly derived coefficients, described the temperature dependence of the shift factor (or Newtonian viscosity) for the temperature range –10 to 60°C. Attempts were made to compare the measured transient response with that calculated from dynamic results. The result of the viscosity test conducted at 45°C as an indicator of modulus at low temperatures was assessed. Surfacing distress increased as the bitumen viscosity or modulus increased, however service performance of the bitumens was best correlated with the modulus calculated at conditions representative of traffic stressing and lowest site temperature. The changes in the rheological properties of bitumens induced by weathering is discussed.     

Rheological properties of network models with configuration-dependent creation and loss rates

A numerical stochastic approach allows the exact solution of the convection equation arising in network theories. We now want to show the flexibility and the limits of this approach by studying the rheological properties of different kinds of models.     

Experimentelle Bestimmung Binghamscher Stoffparameter

An experiment is described to determine the two Bingham material constants (yield stress _f and differential viscosity ) of viscoplastic fluids. The principle of the experiment is based on the falling-ball technique, where the stationary velocities of balls with different diameters and densities are measured. The required theory to calculate the Bingham material constants is illustrated. Experimental results of aqueous Carbopol 941-solutions are reported. These are listed in dependence of concentration in tables and diagrams.

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Zusammenfassung Es wird ein Versuchsaufbau beschrieben, der es ermöglicht, die beiden Binghamschen Stoffparameter (Fließspannung _f und differentielle Viskosität ) einer viskoplastischen Flüssigkeit zu bestimmen. Der Versuch basiert auf dem Kugelfallprinzip, bei dem in einem Zylinder die stationäre Sinkgeschwindigkeit von Kugeln im Schwerefeld gemessen werden. Neben der Geschwindigkeit gehen das spezifische Gewicht der Flüssigkeit sowie die Geometrie und das spezifische Gewicht verschieden großer Kugeln in die Berechnung der Stoffparameter ein. Die zugehörige Theorie wird kurz erläutert. Im experimentellen Teil werden wäßrige Carbopol 941-Lösungen untersucht. Die Ergebnisse sind in Abhängigkeit der Konzentration tabellarisch angegeben und graphisch dargestellt.

     

Peristaltic transport of a power-law fluid: Application to the ductus efferentes of the reproductive tract

The problem of peristaltic transport of a non-Newtonian (power-law) fluid in uniform and non-uniform two-dimensional channels has been investigated under zero Reynolds number with long wavelength approximation. A comparison of the results with those for a Newtonian fluid model shows that the magnitude of pressure rise, under a given set of conditions, is smaller in the case of the non-Newtonian fluid (power-law indexn < 1) at zero flow rate. Further, the pressure rise is smaller asn decreases from 1 at zero flow rate, is independent ofn at a certain value of flow rate and becomes greater if flow rate increases further. Also, at a given flow rate, an increase in wavelength leads to a decrease in pressure rise and increase in the influence of non-Newtonian behaviour. Pressure rise in the case of non-uniform geometry, is found to be much smaller than the corresponding value in the case of uniform geometry. Finally, the analysis is applied and compared with observed flow rates in the ductus efferentes of the male reproductive tract.     

Rheological properties of dilute polymer solutions: An extended thermodynamic approach

It is shown that extended irreversible thermodynamics can be used to account for the shear rate and frequency dependences of several material functions like shear viscosity, first and second normal stress coefficients, dynamic viscosity and storage modulus. Comparison with experimental data on steady shearing and small oscillatory shearing flows is performed. A good agreement between the model and experiment is reached in a wide scale of variation of the shear rate and the frequency of oscillations. The relation between the present model which includes quadratic terms in the pressure tensor and the Giesekus model is also examined.     

Prediction of the non-linear rheological properties of polymer solutions by means of the Rouse-Zimm model with slippage

The non-affine deformation of macromolecules and the slippage function are discussed. In case of polymer solutions with moderate concentration the slippage function is determined by means of the Cox-Merz rule. The non-linear viscoelasticity of these solutions is described with the aid of the Rouse-Zimm model with slippage function. The theoretical predictions show good agreement with published experimental data.     

Rheological characteristics of sewage sludge: A granuloviscous material

Problems have been experienced in the screw conveying of a centrifuge dewatered sewage sludge, at about 66% by weight water content. The rheology of the sludge was therefore tested in a viscometer in which the normal stress between the platens could be controlled. Rough platens were used to measure internal shear strengths while smooth steel platens were used to study wall slip.The sludge displayed a number of the characteristics of a granuloviscous material. It was found to possess high initial shear strength, but rapidly softened with shear to lower steady-state strengths. The initial shear strength increased with increasing normal stress, indicating that the sludge was frictional. The initial strength was lower against the smooth platen.The steady-state shear strengths were both rate and stress dependent using the rough platen, and this internal shear strength could be described by a frictional pseudoplastic equation. Using the smooth platen the material was nearly rate independent, and was best described by a Coulomb friction equation. At the higher rates the wall shear strengths were lower than the internal shear strengths.The strengths (both initial and steady-state) were characterised by a high degree of variability from sample to sample, and also showed marked hysteresis with the rough platen. They did not show any consistent variation with moisture content.In terms of screw conveying, the major conclusion is that smooth walls to the flights of the screw and barrel of the conveyor are desirable.     

Viscometric flows of polymeric melts treated according to the rational theory of Eckart's continuum. I. General theory

The purely rational theory of Eckart continua (i.e. elastic bodies with a variable relaxed state) is applied to viscometric flows of polymeric melts. The main assumptions are thermodynamic non-interaction of inelastic behaviour and of non-elastic stress, as well as elastic isotropy. After establishing the time-dependent differential equations of viscometric flow, these equations are simplified to a set of algebraic equations describing steady-state flow. From this we deduce two general equations connecting the three elastic steady-state viscometric functions which do not depend upon the elastic behaviour. The law of rubber elasticity used in this paper is described in the Appendix.     

Representation of the rheological properties of polymer melts in terms of complex fluidity

In dynamic rheological experiments melt behavior is usually expressed in terms of complex viscosity ^* () or complex modulusG ^* (). In contrast, we attempted to use the complex fluidity ^* () = 1/µ ^* () to represent this behavior. The main interest is to simplify the complex-plane diagram and to simplify the determination of fundamental parameters such as the Newtonian viscosity or the parameter of relaxation-time distribution when a Cole-Cole type distribution can be applied. ^* () complex shear viscosity - () real part of the complex viscosity - () imaginary part of the complex viscosity - G ^* () complex shear modulus - G() storage modulus in shear - G() loss modulus in shear - J ^* () complex shear compliance - J() storage compliance in shear - J() loss compliance in shear - shear strain - rate of strain - angular frequency (rad/s) - shear stress - loss angle - ^* () complex shear fluidity - () real part of the complex fluidity - () imaginary part of the complex fluidity - ₀ zero-viscosity - ₀ average relaxation time - h parameter of relaxation-time distribution     

Evaluating Herschel-Bulkley fluids with the back extrusion (annular pumping) technique

A mathematical model was developed to describe the behavior of Herschel-Bulkley fluids in a back extrusion (annular pumping) device. A technique was also developed to determine the rheological properties (yield stress, flow behavior index, and consistency coefficient) of these fluids. Mathematical terms were expressed in four dimensionless terms, and graphical aids and tables were prepared to facilitate the handling of the expressions.Nomenclature a radius of the plunger, m - dv/dr shear rate, s^–1 - F force applied to the plunger, N - F _b buoyancy force, N - F _cb force corrected for buoyancy, N - F _T recorded force just before the plunger is stopped, N - F _Te recorded force after the plunger is stopped, N - g acceleration due to gravity, m/s² - H(t) momentary height between plunger and container bottom, m - K a/R, dimensionless - L length of annular region, m - L(t) depth of plunger penetration, m - n flow behavior index, dimensionless - p static pressure, Pa - P _L pressure in excess of hydrostatic pressure at the plunger base, Pa - p ₀ pressure at entrance to annulus, Pa - P pressure drop per unit of length, Pa/m - Q total volumetric flow rate through the annulus, m³/s - r radial coordinate, measured from common axis of cylinder forming annulus, m - R radius of outer cylinder of annulus, m - s reciprocal of n, dimensionless - t time, s - T dimensionless shear stress, defined in Eq. (3) - T ₀ dimensionless yield stress, defined in Eq. (4) - T _w dimensionless shear stress at the plunger wall - _p velocity of plunger, m/s - velocity, m/s - mass density of fluid, kg/m³ - Newtonian viscosity, Pa s - P p ₀ –p _L , Pa - consistency coefficient, Pa sⁿ - value of where shear stress is zero - _–, ₊ limits of the plug flow region (Fig. 1) - r/R - shear stress, Pa - _y yield stress, Pa - _w shear stress at the plunger wall, Pa - dimensionless flow rate defined in Eq. (24) - dimensionless velocity defined by Eq. (5) - _–, ₊ dimensionless velocity outside the plug flow region - _max dimensionless maximum velocity in the plug flow region - _p dimensionless velocity at the plunger wall     

Rheological and drag reduction characteristics of xanthan gum solutions

The rheological and turbulent drag reducing characteristics of commercial and purified xanthan gum solutions of concentrations 50–500 ppm have been studied with and without addition of 100 ppm NaCl. The purification by soxlet extraction of xanthan gum using 95% ethanol is effective in removing low-molecular-weight impurities from xanthan. The increased content of higher molecular-weight xanthan in purified xanthan is evident from rheological and drag reduction behavior. The addition of 100 ppm salt to dilute solutions introduces semi-flexibility in xanthan gum solution without occurrence of self-association. The change in molecular behavior in the presence of salt is evident from rheological normal-stress and turbulent drag reduction behaviors.