Showing papers on "Rheometer published in 1977"

Self-diffusion of particles in shear flow of a suspension

Abstract: Self-diffusion coefficients were determined experimentally for lateral dispersion of spherical and disk-like particles in linear shear flow of a slurry at very low Reynolds number. Using a concentric-cylinder Couette apparatus, recurrent observations were made of the lateral position of a particular radioactively labelled particle. The self-diffusion coefficient D was calculated by means of random-walk theory, using the ergodic hypothesis. Owing to great experimental difficulties, the calculated values of D are not of high accuracy, but are correct to within a factor of two. In the range 0 < ϕ < 0·2, D/a2ω increases from zero linearly with ϕ up to D/a2ω ≅ 0·02 (where ϕ = volumetric concentration of particles, a = particle radius, ω = mean shear rate of suspending fluid). In the range 0·2 < 0·5, the trend of D/a2ω is not clear because of experimental scatter, but in this range D/a2ω ≅ 0·025 to within a factor of two. Within the experimental accuracy, spheres and disks have the same value of D/a2ω.

Glass bead-filled polypropylene part I: Rheological and mechanical properties

Abstract: Five glass bead-filled polypropylene composites were rheologically characterized at 240°C using two rotational rheometers to obtain low shear-rate data and a capillary rheometer to obtain high shear-rate data. Both steady and dynamic properties were measured at low shear rates. Each composite was also injection molded into tensile and flexural test bars for a mechanical properties profile at 25°C. The tensile modulus was determined from a simple extensional deformation whereas the flexural modulus was determined from a three-point-bend test. The relative shear viscosity and relative loss modulus are different nonlinear functions of the volume fraction of beads at a constant shear rate, while the relative storage modulus appears to be a linear function of bead fraction. The relative viscosity decreases with increasing shear rate and the zero shear-rate data are in very good agreement with the Guth-Gold equation. The relative tensile modulus and relative flexural modulus are each linear functions of bead fraction over the entire range of filler concentration, 0-29 vol percent. From these data it is concluded that a simple correspondence between slow viscous flow and small strain elasticity does not exist for these composites.

Separation of Elastic and Shear Thinning Effects in the Capillary Rheometer

Abstract: The influence of elasticity in the absence of shear thinning on the total extra losses (end correction) in a capillary rheometer is investigated. Fluids with the unusual characteristic of being elastic but not shear thinning are used. Independent property measurements made with an R16 Weissenberg rheogoniometer are used to quantify the behavior of these fluids. The end correction in the absence of shear thinning is found to be constant with shear rate in the lower shear rate region and to decrease slightly at higher shear rates. The intercept of the end correction shear rate plot is significantly higher than the Newtonian fluid value and is shown to be directly related to the fundamental elastic properties of the fluid. The end correction is measured for a material which exhibits the properties of a second‐order fluid in steady shear. The influence of shear thinning in the presence of fluid elasticity is found to increase the end correction. A method for correlating end correction data is proposed which is consistent with the results obtained by other investigators.

Experimental tests of constitutive relations for polymers undergoing uniaxial shear flows

Abstract: Stress development at the onset of steady shear flow and stress relaxation from steady state were measured in a stiffened Weissenberg Rheogoniometer over wide ranges of shear rate for three polystyrene solutions. Time dependent shear stressσ and first normal stress differenceN 1 were obtained from the torque and axial thrust. From extensive auxiliary tests we believe these data to be free of spurious effects associated with instrument compliance. The solutions have zero shear viscosities of 890, 3900 and 67 000 poise. Tests for consistency with strain rate constitutive models were made using thevan Es-Christensen relation and with relative strain models using theKearsley-Zapas relations. Substantial deviations were found in both cases. TheMarrucci model was also examined. As in theCarreau model B, the predicted start-up curves from theMarrucci model are in general qualitative accord with observations, but some systematic quantitative discrepancies remain.

Barus effect in polymer flows through cylindrical and flat dies

Abstract: The determination of the swell factor of a polymer jet extruded from a cylindrical or flat die is examined. Relations are obtained for the dependence of the swell factor on shear rate and shear stress, expressed in terms of the constants of the rheological model.

Capillary flow of poly(vinyl chloride) compounds. A comparison with viscometric flow data measured in continuous shear

Abstract: An investigation of the flow curves for rigid and plasticized compounds of PVC has shown that capillary rheometry on “fused” compounds is in accordance with data obtained in continuous shear. It is further concluded that the S-shaped flow curves (log shear stress against log shear rate) that can be observed are caused by the existence of stable crystallite aggregates at low temperatures and shear rates and nonisothermal conditions at high shear stresses and high shear rates.

Lubricant rheology applied to elastohydrodynamic lubrication

Abstract: Viscosity measurements in a high pressure rheometer, elastohydrodynamic simulator studies (including the development of a temperature measuring technique), and analytical fluid modeling for elastohydrodynamic contacts are described. The more recent research which is described concerns infrared temperature measurements in elastohydrodynamic contacts and the exploration of the glassy state of lubricants. A correlation, of engineering significance, was made between transient surface temperature measurements and surface roughness profiles. Measurements of glass transitions of lubricants and the study of the effect of rate processes on materials lead to the conclusion that typical lubricants go into the glassy state as they pass through the contact region of typical elastohydrodynamic contacts.

Viscoelastic Characterization of Ethylene-Propylene-Diene Terpolymer Elastomers

Abstract: A practical range of frequency with the Rheometric mechanical spectrometer for the determination of G′ and G″ was shown to be from 2.5×10−2 to 2.5×102s−1, but one decade lower frequency may be reached routinely. The values G′ and G″ may be calculated from the steady-state viscosity curve obtained with the variable-speed Mooney rheometer. However, with samples having long-chain branching, the calculated G′ and G″ are somewhat higher, the difference being close in magnitude to the error of the measurements. With the variable-speed Mooney rheometer, the highest available shear rate is 16 s−1, about one decade less than that with the Rheometrics instrument. With high-molecular-weight rubbers, the range is further reduced, because of “slipping” or “fracturing” of the polymer. On the other hand, the Mooney rheometer enables one to extend the low-frequency range to 2×10−3s−1 very conveniently. The degree of long-chain branching may be estimated from the viscoelastic behavior by comparing complex viscosi...

Apparatus for concurrent measurement of polymer melt

Abstract: a polymer melt's rheological properties are comprehensively described by defining the constants K and n in the rheological equation: T= KGn where T= shear stress and G= shear rate. The constants are determined by a rheometer which divides a molten polymer sample into two streams pumped by positive displacement pumps having identical speed-displacement characteristics past pressure transducers and finally through dissimilar capillaries to atmosphere. The pressure in each line is regulated at a predetermined level. Pressure and tachometer readings are used to compute the constants K and n.

Falling coaxial cylinder viscometer with wide shear rate range

Abstract: A novel viscometer was devised to measure flow curves of polymer melts over a wide range of shear rates. The apparatus comprises a concentric cylinder viscometer with the inner moving piston driven axially at set speeds. Immersion depth of the moving piston increases continuously during the course of an experiment. An Instron or similar piston-operated capillary viscometer can be easily modified for this purpose.

Viscous Dissipation in the Flow Between Eccentric Rotating Disks (Orthogonal Rheometer)

Abstract: The orthogonal rheometer has become increasingly popular for determination of the viscoelastic properties of fluids. Here we present an analytical solution for the steady‐state temperature distribution arising from the dissipation due to flow between infinite, isothermal eccentric rotating disks. This information is necessary to experimentalists concerned with obtaining accurate rheological characterizations for materials whose properties are temperature dependent, e.g., polymer melts. The results, temperature profiles and the maximum temperature rise, are presented using two dimensionless parameters which indicate the effects of inertia and fluid elasticity. Thus, the results can be easily used by practitioners to estimate the importance of dissipation in their experiments. For conditions of practical interest, temperature rises large enough to be of concern may be encountered.

Effect on flow properties of tin-stabilized rigid PVC by PE paraffins having different degrees of branching

Abstract: The processing properties of a rigid PVC compound with various amounts of different lubricants were studied with a torque rheometer. The plasticizing behavior was measured in a mixer and recorded as torque versus time. The fusion time and the torque at fusion and of the molten material were evaluated. The compounds were extruded with a laboratory extruder and a capillary die. The torque of the screw, the melt pressure, and temperature in the barrel and the die and the output were measured. The shear stress and shear rate were calculated from these results. The lubricants, one paraffin and five polyethylenes, had molecular weights of 700 to 3500. The dependence of the processing behavior on the molecular weight of the lubricants is discussed. There is no single value which can be given but numerous interdependent parameters can be used to obtain a prediction of the processing properties of the material.

Low temperature rheology of asphalt cements: stiffness and viscosity

Abstract: Stiffness, as a material characteristic of asphalt cements, is attracting more attention in asphalt technology. This paper shows the quantitative relations between viscosity and stiffness and explains how the shear modulus and viscosity found by a constant stress rheometer can be used to evaluate stiffness. Experimental data from creep curve studies are given for a number of asphalt cements. The shear modulus is shown as the limiting asymptote that intersects the viscosity term asymptote at a stiffness limit time. These two asymptotes delineate the complete stiffness curve. Characteristic stiffness is shown to be a material property, but knowledge of the system is prerequisite to its use in design, if the absolute deformation is to be considered. Variations in stiffness with shear rate (stress), temperature, and time are illustrated by data on absolute measurments for eight different types of asphalts at temperatures from 25 down to -5 deg C (77 to 23 deg F). The addition of vicosity and stiffness data at 5 deg C (41 deg F) to the usual viscosity data at 25 and 60 deg C (77 and 140 deg F) provides a better rheological profile for asphalt cements at low ambient temperatures than has previously been reported. /Author/

Extrusion rheometer for characterizing thixotropic materials

Abstract: A special form of extrusion rheometer has been developed for characterizing thixotropic pastes and high viscosity materials. It consists of a cylinder with an orifice situated halfway along, and has a piston at each end. In use, a sample plug of material is forced through the orifice at a uniform rate by one of the pistons, and the load required is recorded. After a given recovery period the material is forced back through the orifice by the other piston, and the load again recorded. If the material is thixotropic, it will have a reduced viscosity on the second ’’pass,’’ and the percentage reduction in load will be related to the thixotropy of the sample. This rheometer was developed for testing resin adhesive pastes, but other possible applications might include the testing of paints, foodstuffs, cosmetics, toothpaste, printing inks, and greases.