Showing papers in "Rheologica Acta in 1981"

Shear flow properties of concentrated solutions of linear and star branched polystyrenes

Abstract: The linear viscoelastic and viscometric functions have been determined for solutions of wellcharacterized monodisperse linear and star-branched polystyrenes and for commercial, polydisperse polystyrene. The value of the product c\(\bar M_w \) for these solutions was large and was obtained by using both high and low\(\bar M_w \)

An empirical equation of the relative viscosity of polymer melts filled with various inorganic fillers

Abstract: Based on Maron-Pierce's equation, an empirical equation was suggested, which relates the relative viscosity (ηr) of the polymer melt filled with various inorganic filler, such as glass fiber, carbon fiber, talc, precipitated- and natural-calcium carbonate powder, and glassy small sphere, to the volume fraction (φ) of the filler. The equation isηr = (1 −φ/A)−2, whereA is a parameter relating to the packing geometry of the filler, which is similar to the parameterφ0 in Maron-Pierce's equation. In the equationηr is defined as the ratio of the viscosity of the filledsystem to that of the medium at the same shear stress not the shear rate. The applicability of the equation is above the shear stress about 104 dyne/cm2. The equation has a simple form and is considered to have a practical utility for filled-polymer melt systems.

Elongational properties and molecular structure of polyethylene melts

Abstract: The viscosity and the recoverable strain in the steady state of elongation have been measured on several polyethylenes of different molecular structures. The elongational viscosity as a function of tensile stress runs through a more or less pronounced maximum in the nonlinear range whereas in the linear range the Trouton viscosity is reached. For low density polyethylenes it could be demonstrated that the maximum of the steady-state elongational viscosity and the elasticity expressed by the steady-state compliances in shear and tension sensitively increase if the molecular weight distribution is broadened by the addition of high molecular weight components. A variation of the weight average molecular weight does only shift the elongational viscosity curve but leaves its shape unchanged. Two of the four high density polyethylenes investigated do not show a maximum of the steady-state elongational viscosity, for the others it is less pronounced than in the case of low density polyethylenes. The influence of branching on the elongational behaviour of polyethylene melts in the steady-state and the transient region is qualitatively discussed.

Viscoelastic behaviour of wheat starch pastes

Abstract: The dynamic mechanical behaviour of starch pastes has been investigated over a frequency range of 0.02 to 5.0 radian sec−1. The influence of concentration of starch, source of starch and method of paste preparation on rheological properties have been studied. The results suggest that under the conditions examined differences in the dynamic rigidity and viscosity of pastes may be attributed to differences in the number fraction of large granules and the volume fraction of swollen starch particles they contain.

The rheology of suspensions of vinylon fibers in polymer liquids. I. Suspensions in silicone oil

Abstract: The steady shear flow properties of suspensions of vinylon fibers in silicone oil were measured by means of a cone-plate type rheometer. Three kinds of vinylon fibers used had no distributions of length and were more flexible than glass fibers and the like. The content of the fibers ranged from 0 to 7 wt.%. Shear viscosity, the first normal-stress difference, yield stress, and relative viscosity were discussed. Shear viscosity and relative viscosity increased with the fiber concentration and the aspect ratio, and depended upon the shear rate. The applicability of Ziegel's equation of viscosity for fiber suspensions was investigated. The first normal-stress difference increased with the fiber concentration, aspect ratio, and shear rate and its relative increase was much larger than for shear stress and viscosity depending on the properties of the characteristic time, $$\bar \tau $$ The yield stress could be determined by Casson plots for large aspect ratio fiber suspensions even in low concentration comparing with the suspensions of spherical particles or powder. The influence of the flexibility of the fibers for the rheological properties of the fiber suspensions can not be ignored.

Transient shear flow behavior of polymeric fluids according to the Leonov model

Abstract: The viscoelastic behavior of polymeric systems based upon the Leonov model has been examined for (i) stress growth and relaxation with intermittent shear flow, (ii) stress relaxation after a step in the shear strain and (iii) elastic recovery after shear flow. A large number of modes have been conveniently incorporated through the determination of the model parameters from conventional rheological data by using an effective least-square procedure. With a sufficient number of modes, the predictions are in very good agreement with corresponding experiments in literature, including the recent data for cases (i) and (ii) obtained by optical methods.

Dehnströmungen mit verdünnten Polymerlösungen: Ein theoretisches Modell und seine experimentelle Verifikation

Abstract: Es werden theoretische Uberlegungen zusammenfassend dargestellt, welche die Streckung und Ausrichtung von flexiblen Makromolekulen in stationaren einfachen Dehnstromungen beschreiben. Die Makromolekule werden hierbei als EDNE-(endlich dehnbare, nichtlinear elastische) Hanteln modelliert. Fur den Fall niedriger bzw. hoher Dehnungsraten werden Dehnviskositatsgleichungen fur Stromungen mit verdunnten Polymerlosungen angegeben.

On the effective viscosity of pseudoplastic suspensions

Abstract: An expression is developed that predicts the concentration dependence of the apparent viscosity of a concentrated pseudoplastic suspension. The result, which is an extension of the Frankel and Acrivos Newtonian suspension analysis, shows that the influence of particles concentration on the effective viscosity of pseudoplastic suspensions increases as the power law index of the suspension increases. Experimental data shows good agreement with the theoretical predictions.

Simultaneous measurement of transient stress and flow birefringence in one-sided compression (biaxial extension) of a polymer melt

Abstract: Investigation of time dependent behaviour of a polystyrene melt is carried out with the aid of a new apparatus for biaxial extension. Use is made of the method of two impinging fluid streams guided by lubricated trumpet shaped metal walls. The flow birefringence is measured in the plane of symmetry and, at the same time, the force is measured which tends to separate the trumpets. The linear stress-optical relation turns out to be valid in this new flow geometry. An accurate value for the stress-optical coefficient can be determined from the relaxation experiments. The stress build-up as calculated from the optical measurements, is compared with the pertinent result of the theory of linear viscoelasticity. For the desired interconversion of dynamic moduli use is made of the approximation by Schwarzl and Struik. The steady state measurements are checked by the results of the non-linear model of Acierno et al.

The stick-slip problem for a round jet

Abstract: The stick-slip problem for a round jet studied in Part I gives a good approximation for the swell of a low speed jet when the surface tension is large but it fails when the surface tension is small. In this paper a new stick-slip problem (II) is defined and solved using matched eigenfunction expansions. The new problem reduces to that solved in Part I when the surface tension is large and gives good results in the case of zero and small surface tension.

Creeping motion of spheres through Ellis model fluids

Abstract: Experimental results for creeping motion of spheres through Ellis model fluids are compared with the theory of Hopke and Slattery. For 58 data points in the required range of 1 ⩽α ⩽ 3, andEl ⩽ 10, the average of the bounds agrees with experiment with a maximum deviation of 20% and an average deviation of 9%. For smallEl, the data points are found to fall near the upper bound while for largeEl they fall near the lower bound.

Determination of turbulent pressure loss of non-newtonian oil flow in rough pipes

Abstract: A detailed theoretical analysis is carried out of the turbulent flow of non-newtonian fluids in rough pipes in which approximate assumptions are of negligible importance. A new friction-factor equation (BNS-equation) is obtained which is valid for turbulent flow of “power-law type” non-newtonian fluids in the transition region between smooth and wholly rough wall turbulence.

The rheology of suspensions of vinylon fibers in polymer liquids. II. Suspensions in polymer solutions

Abstract: The rheological properties of vinylon fiber suspensions in polymer solutions were studied in steady shear flow. Shear viscosity, first normal-stress difference, yield stress, relative viscosity, and other properties were discussed. Three kinds of flexible vinylon fibers of uniform length and three kinds of polymer solutions as mediums which exhibited remarkable non-Newtonian behaviors were employed. The shear viscosity and relative viscosity (ηr) increased with the fiber content and the aspect ratio, and depended upon the shear rate. Shear rate dependence ofηr was found only in the low shear rate region. This result was different from that of vinylon fiber suspensions in Newtonian fluids. The first normal-stress difference increased at first slightly with increasing fiber content but rather decreased and showed lower values for high content suspensions than that of the medium. A yield stress could be determined by using a modified equation of Casson type. The flow properties of the fiber suspensions depended on the viscosity of the medium in the suspensions under consideration.

A finite element computer model of the hole pressure problem

Abstract: This paper extends some earlier work in which consideration was given to the flow of a second-order visco-elastic liquid through a channel composed of two parallel plates, one plate having a rectangular slot cut into it perpendicular to the flow direction. In the present work the problem is re-solved for the case of an implicit Oldroyd-type model and solutions obtained using a numerical finite element technique. Severe numerical convergence difficulties are encountered when the elasticitiy of the liquid is increased. The relationship between the ratio of the hole pressure to first normal-stress difference and the Reynolds number is investigated for both Newtonian and elastic liquids and the results compared with a simple analytical analysis of Tanner and Pipkin and with the second-order fluid results of the previous paper. It is found that the value of this ratio falls as the Reynolds number is increased from zero up to 10 but that the rate of decay is less than for the second-order liquid. However in the present work elasticity is found to have a significant effect even at small Reynolds numbers, so that the ratio can deviate quite considerably from the Tanner-Pipkin theoretical value of 0.25. Streamline patterns plotted for various flow conditions indicate that both inertia and elasticity bring about an asymmetry in the streamlines which dip into the hole, and in the vortex contained within the hole, but that the two factors work against one another so that it is possible for an elastic liquid to see a symmetric pattern for Reynolds numbers considerably beyond the range of the Tanner-Pipkin theory.

Flow characteristics of primary and digested sewage sludge

Abstract: Rheological study of sewage sludge is useful for the design, operation and control of sewage treatment plants. The rheology is highly dependent on physical, chemical and biological characteristics of the sludge. A pipeline rheometer is described in this paper for measurement of rheological properties of the sludge. Primary sewage sludge is a complex flocculated suspension having no fixed particle dimension, shape, size distribution or surface characteristics. The information available so far on rheology of sewage sludge is not suitable for application in design because of the lack of data on physico-chemical characteristics of this sludge.

Uniaxial extension of linear flexible-chain polymers in an extremely broad range of stresses and strain rates

Abstract: This work summarizes the basic patterns of strainstrength behaviour of linear flexible-chain polymers at uniaxial extension. The boundaries of transition of non-cross-linked polymers under isothermal conditions from the fluid to the high-elastic and leathery states when an axial load is applied are defined. A relationship is established between the parameters of longitudinal and low-amplitude strains. A study is made into the effect of molecular parameters and liquid media on the deformation and rupture of non-cross-linked linear polymers.

Sulfur modified bitumen: A new binder

Abstract: Bitumen is modified after a treatment with 2% sulfur, at 160°C. It is more plastic consecutive to a variation of the nature of the interactions between asphaltene molecules.

The recovery after bending of polycarbonate sheets

Abstract: The recovery after bending has been extensively studied for metal sheets. The data presented in this work show that in the case of polymeric materials viscoelastic effects play a very important role. In particular the influence of deformation rate, the time the sample is held under load and the recovery time is analysed. A master curve is obtained by proper modification of a recent analysis developed for metal sheets.

Effect of sodium hydroxide pretreatment on the relaxation spectrum of concentrated agar-agar gels

Abstract: Stress relaxation and ultrasonic absorption measurements were made for agar-agar pretreated by various concentrations of sodium hydroxide, in order to clarify the dominating factors in its rheological properties. Stress relaxation measurements were made up to 30 hours. Relaxation spectra were obtained by the reduced variable method. Gels prepared from agar-agar pretreated by concentrated sodium hydroxide show a larger relaxation modulus than those pretreated by dilute sodium hydroxide and those without alkaline pretreatment. It is suggested that hydrogen bonds are newly created as a result of desulfation in the molecule, and then, the microcrystalline structure is stabilised.

Über die Stabilität viskometrischer Strömungen

Abstract: Die Stabilitat der ebenen Couette- und der ebenen Poiseuille-Stromung nicht-newtonscher Fluide wird fur kleine Storungen in der viskometrischen Ebene untersucht. Der Einflus der Relaxationszeit der Storungen wird vernachlassigt. Es wird gezeigt, das die ebene Couette-Stromung unabhangig von der ReZahl instabil wird, fallsd(κN)/dκ > 4ηη >d gilt. Hier bedeutenκ die Schergeschwindigkeit,N den ersten Normalspannungskoeffizienten,η die Viskositat undη d die differentielle Viskositat (η d =dτ/dκ). Das gleiche Kriterium gilt mit den Daten an der Kanalwand auch fur die Poiseuille-Stromung. In diesem Fall oszillieren die Eigenfunktionen in einer sehr dunnen, wandnahen Schicht und klingen im Flussigkeitsinnern sehr rasch ab.

Memory effects during the flow of thixotropic fluids in pipes

Abstract: The paper presents the phenomenon of thioxotropy from the point of view of the theory of fluids with fading memory. In the first part of the paper the mechanism of thixotropy was discussed in order to justify the application of the concept of structural parameter (this parameter occurs in the previously presented rheological model of thixotropic materials). In the second part of the paper an equation was derived, which enables the prediction of the mean value of the friction factor during the flow of a thixotropic fluid in a pipe. According to the obtained equation the friction factor is a function of three dimensionless numbers: the generalized Reynolds number, a modified Deborah number and a new dimensionless number which may be called a structural number. The preliminary experimental results confirmed the applicability of the obtained equation.

Rheologische Untersuchungen an Polyacrylnitril-Spinnlösungen: Erweiterung des Viskosimeters HV 6 für höhere Temperaturen

Abstract: Das Hochdruckkapillarviskosimeter HV 6 wurde fur Messungen bei hoheren Temperaturen adaptiert; dadurch konnten konzentrierte Losungen von Polyacrylnitril in Dimethylformamid bis zu 120°C vermessen werden. Die erhaltenen Resultate wurden nach der Methode Vinogradov-Malkin normiert; gewisse Abweichungen, die hierbei auftraten, konnten durch Einfuhrung eines empirischen Zusatzverschiebungsfaktors korrigiert werden.

Zur Aufstellung von Stoffgleichungen in der Kriechmechanik anisotroper Körper

Abstract: Der Aufsatz vermittelt einen kurzen Uberblick uber mogliche Darstellungsformen von Stoffgleichungen unter Einbeziehung der Anisotropie und etwaiger Kriechschaden. Bei der Aufstellung von Stoffgleichungen werden Darstellungstheoreme von Tensorfunktionen zugrunde gelegt. Fur praktische Anwendungen wird eine vereinfachte Theorie skizziert.

The site model theory and the standard linear solid

Abstract: The site model theory (SMT) is shown to lead to the same deformation behaviour as that displayed by the standard linear solid (SLS), group I, for all loading conditions. If a second deformation mechanism (inter-molecular slip) is introduced the result is the same as that obtained with the standard linear solid, group II, and models the behaviour of a polymer melt near to the solidification temperature.

Rheological studies of coal-oil mixtures

Abstract: Samples of stable coal-oil mixtures were prepared with coal concentrations ranging from 30–50% by weight. Extensive rheological data were obtained using capillary and cone-plate viscometers for samples of coal-oil mixtures and fuel-oil which served as a reference fluid. Viscosity measurements show coal-oil mixtures to be shear-thinning suspensions, i.e., the viscosity decreases moderately with increasing shear rates. In the concentration range of 30–40% coal, the coal-oil mixture shows a predominantly Newtonian behavior. For mixtures with coal concentrations higher than 40%, a yield point was observed. The study of these samples with the rotating-rod viscometer indicated a migration of coal particles away from the rotating rod with no noticeable rod climbing, thus no evidence of normal stress effects. The rheological data can be represented by any of the three two-parameter models: Power Law, Bingham Plastic, or Casson, with the last two models being more realistic and consistent with the observations.

Correlation of data concerning resistance to flow of generalized Newtonian fluids through granular beds

Abstract: The paper is concerned with the pressure drop during the flow of rheologically complex fluids through granular beds. An approach is proposed which enables the correlation of the data for any generalized Newtonian fluid. As an example, a detailed derivation of a correlation equation is presented for Carreau fluids. The applicability of the derived equation was proved experimentally in the case of flow of molten poly(ethylene terephthalate) through granular beds.

The fluidity of molten salts

Abstract: The fluidity,φ, of a molten salt is directly proportional to the relative free volume (V − V0)/V0. Although the parameterV0 is closely related to the molar volume of the solid near the melting point the proportionality constant is difficult to interpret in terms of the microscopic or thermodynamic properties of the salt.

On the measurement of normal stress differences in steady shear flow

Abstract: Compared to the similar pressure-distribution cone-and-plate apparatus of Adams and Lodge (4), the new apparatus' improvements include: temperature control of the cone (as well as the plate); increased stiffening of the frame; four (not three) pressuremeasuring holes in the cone/plate region; inclusion of a pressure-measuring hole on the axis under the cone truncation; exclusive use of a vertical free liquid boundary at the cone rim (without a “sea” of liquid). Temperature control of the rotating cone and of the fixed plate leads to acceptable temperature uniformity in the test liquid for working temperatures within 10°C or 20°C of ambient; the corresponding interval is about 1°C if the cone temperature control is abandoned. Pressure gradients measured using a Newtonian liquid agree with those calculated using Walters' eq. (3). For a viscoelastic liquid, after subtracting inertial contributions, pressure distributions measured at a given shear rate in the cone/plate region do not change when the gap angle is changed from 2° to 3°, showing that the effects of secondary flow are negligible. Values ofN 3 =N 1 + 2N 2 obtained from the gradients of these distributions are believed to be in error by not more than ±1 Pa, in favorable cases. The present most useful ranges are: 10 to 5000 Pa forN 3; 0.1 to 200 sec−1 for shear rate; up to 5 Pa s for viscosity; and 5 to 40°C for temperature. As an application, it is shown that adding 0.1% of a high molecular weight polyisobutylene to a 2% polyisobutylene solution doublesN 3 and has no detectable effect on the viscosity measured at low shear rates with a Ferranti-Shirley viscometer.

Scattered light streaming birefringence in colloidal solutions

Abstract: The light scattered from particles or molecules in a fluid flow is often used to perform local measurements in a three-dimensional flow field. The scattered light technique has been adopted by McAfee and Pih to the field of streaming birefringence. Their empirical relationship between the observed optical pattern and the state of the flow is extended here to describe more general flow situations. The new set of equations which includes all possible shear and dilatation terms is tested with a number of experiments in the flow of a colloidal solution. The range of validity of these equations is restricted to low-Reynolds number flows.