Showing papers on "Rheometer published in 1986"

Prediction of Elastic Strains of Polymer Melts in Shear and Elongation

Abstract: Transient and steady‐state recoverable strains in shear and uniaxial elongation were measured with rheometers of different type. Results on melts of linear and branched polyethylenes, polypropylene, polystyrene, polyamide 6, and a PIB solution are reported. To represent the linear viscoelastic behavior, the essential basis of the theoretical treatment, discrete relaxation time spectra have been determined from the dynamic moduli in oscillatory shear. Calculations of the primary normal stress and of the shear and elongational viscosities in the non‐Newtonian range are based on a single integral constitutive equation with strain‐dependent memory function. Recoverable strains observed after unloading the samples from steady‐state flow are calculated by means of a quasilinear treatment of the materials, making use of deformation rate dependent effective relaxation strengths. The agreement of predicted and measured recoverable strains over a very wide range of shear and elongation rates strongly supports this new concept, which does not involve an inversion of the integral constitutive equation. In addition, the applicability of two empirical equations that relate the primary normal stress coefficient and the recoverable strain in steady shear flow to the dynamic moduli are checked on the same materials.

Some Rheological Measurements on Magnetic Iron Oxide Suspensions in Silicone Oil

Abstract: A model magnetic suspension was formulated with acicular γ‐Fe2O3 particles dispersed in silicone oil Four volume fractions (24, 53, 87, and 129%) were studied in steady shearing over a wide range in rate (10−5 to 10+3 s−1) using a Rheometric System Four Rheometer At medium rates instabilities in both cone and plate and parallel plate were observed At low rates (<10−1 s−1) the stress became independent of rate indicating yield behavior Yield stresses of 025, 4, 5, and 20 Pa were estimated for the four samples On the 129% sample a yield stress of 20 Pa was also found using small amplitude sinusoidal oscillations and with a constant stress rheometer Below this yield value, solid‐like elastic behavior was observed

The Significance of Aggregate Properties to Transport Processes

Abstract: Aggregates of cohesive suspended particles in estuarial waters are formed by Brownian motion, differential settling, and velocity gradients. Aggregates formed by Brownian motion and differential settling are weak and have low densities, compared to those formed in moderate velocity gradients. The densities and shear strengths of aggregates formed in a range of velocity gradients were measured using a capillary viscometer and a concentric cylinder viscometer. It was found that different aggregate structures could exist over short ranges of velocity gradients, and that the structures stable at lower ranges of velocity gradients had lower shear strengths and lower densities. The structures can be described as aggregates of aggregates, with successively higher orders at successively lower ranges of velocity gradients.

Shear-wave speeds and elastic moduli for different liquids. Part 2. Experiments

Abstract: Tables of values of shear-wave speeds, shear moduli and relaxation times for 18 new liquids are presented, supplementing the tables for 51 liquids given in Part 2. A brief discussion of errors and analysis of the oscilloscope traces is presented. The relation of the effective moduli measured on the wave-speed meter to independent measurements using phase-modulated birefringence and delayed die swell is discussed. A method of measuring wave speeds and rigidities for sheared media is proposed.

Steady Shear Rheology and Fluid Mechanics of Four Semi‐Solid Foods

Abstract: The steady shear rheology of four semi-solid food materials (ketchup, mustard, apple sauce and tomato paste) was studied by generating and comparing flow data using cone and plate, parallel plate and capillary measurements over the shear rate range of 0.05–1600 see−1. Super-position of flow data was demonstrated and correlations obtained; using the power law, Bingham Plastic, Herschel-Bulkley and Casson models were compared. In the low shear rate range (y = 0.05 – 1.0 set−1), the Bingham Plastic model and in the high shear rate range (y = 1.0 – 1600 sec−1), the Herschel-Bulkley model were shown to be most successful. Comparison of average velocity data with mathematical predictions using the power law, Herschel-Bulkley and Cas-son models showed that the equation using the Herschel-Bulkley model was best and should be used in the design of flow processes for the foods studied.

Polymer Compounding Process for Controlled Peroxide-Degradation of PP

Abstract: A process control concept for peroxide-initiated degradation of polypropylene was presented. The link-up of a twin-screw extruder to an on-line Rheometer and a computer system using a newly developed program package can he used to form a process control system unaffected by external disturbing influences and leading to a long-term constant product quality. Work is still to be done concerning development and optimization in the area of layout and design of adapter systems and concerning the measures for lowering the controllability ratio Z1 Special attention should be given to a processing concept to enable changes in w and MWD independently of one another.

Rheology of hydroxypropylcellulose solutions

Abstract: The rheology of hydroxypropylcellulose (HPC)—acetic acid solutions was investigated by using a cone-and-plate rheometer and a capillary rheometer, for polymer concentrations ranging from 10 to 80%. Isotropic solutions exhibit a Newtonian plateau followed at higher shear rates by a pseudoplastic zone. The apparent viscosity varies as C5.2 if concentration C is less than 27% and as C13 for 27% < C < 30%. A biphasic interval (isotropic and cholesteric phases) exists between 30 and 35%. A maximum in viscosity is observed at C = 30%, the height of the viscosity peak being a decreasing function of shear rate. Anisotropic solutions are strongly viscoelastic. Both isotropic and anisotropic solutions give results (apparent viscosity, first normal-stress difference, relaxation time, etc.) which are not in good agreement with Doi's theory. This is understandable since the HPC chain cannot be modeled by a rigid rod. Upon heating, anisotropic HPC—acetic acid solutions undergo an anisotropic to isotropic phase transition which is easily detected by a maximum in the temperature dependence of the first normal-stress difference and of the apparent viscosity.

Shear dependence of viscosity for perfluoropolyether fluids

Abstract: The shear dependence of the bulk viscosities of two structurally different types of perfluoropolyether fluids was determined by two different techniques. The first involved direct measurement in a high shear Couette viscometer, the second utilized the time-temperature superposition principle to establish master curves from viscosity determinations at low shear rates and temperature; the results are comparable. Both fluids begin to show non-Newtonian behavior at shear rates above 10,000 s−1.

Slip flow of non-plasticized PVC compounds

Abstract: Measurements on seven rigid PVC compounds were carried out with a slit rheometer working in combination with an injection moulding machine. Plastication of the compounds occurred in the screw of the plastication unit, which also forced the melt through the die with a controlled forward velocity. The rectangular slit had a length of 90 mm and a widthB of 20 mm. The heightH could be varied between 0.8 and 3.3 mm. Pressures and temperatures were recorded at several positions in and before the die. Measurements were carried out at shear rates from 10 to 2000 s−1.

Viscometer for low frequency, low shear rate measurements

Abstract: A computer-controlled torsion-oscillator viscometer with low 0.5 Hz frequency and very low 0.05/s shear rate is designed to precisely study shear-sensitive fluids such as microemulsions, gels, polymer solutions and melts, colloidal solutions undergoing coagulation, and liquid mixtures near critical points. The viscosities are obtained from measurements of the logarithmic decrement of an underdriven oscillator. The viscometer is found to have a resolution of 0.2 percent when used with liquid samples and a resolution of 0.4 percent when used with a dense gaseous sample. The design is compatible with submillikelvin temperature control.

Flow of viscoelastic fluids between plates rotating about distinct axes

Abstract: We discuss the flow of BKZ fluids in an orthogonal rheometer. Some analytical results are proved, and numerical solutions are obtained for the Currie model. These solutions show a boundary layer behavior at high Reynolds numbers and the possibility of discontinuous solutions or nonexistence at high Weissenberg numbers.

The viscosity of concentrated polymer solutions containing low molecular weight solvents

Abstract: The zero shear rate viscosities of polystyrene/ethylbenzene solutions having polymer weight fractions ranging from 0.5 to 1.0 have been measured using a novel sealed rheometer cell over a temperature range of 50 to 200°C. The concentration and temperature dependence of the solution viscosity has been found to be well described by the relation η0 = K caMw3.4ζ(c, T) where the monomeric friction coefficient ζ is determined by the free volume of the solution. Following the procedure of Berry, the free volume parameters, αf(c)/γ and T∞ (c), and the fractional free volume, f(c,T)/γ, have been determined. After using these parameters to account for the concentration dependence of the friction coefficient, the concentration exponent a has been evaluated and found to be in reasonable agreement with the value of 3.4 obtained by Berry and Fox for other polymer/solvent systems. A comparison of the relative conributions made by the friction coefficient and the term c3.4 to the overall concentration dependence of the viscosity of these highly concentrated solutions shows the friction coefficient to be the dominant factor

The viscoelastic properties of PP/glass fiber composites in molten state

Abstract: The molten viscoelastic behavior of polypropylene/glass fiber composites (FRPP) were investigated under steady state and dynamic state. The steady viscosity was measured from both cone-plate rheometer and capillary flow tester. The dynamic viscoelastic properties were measured from cone-plate rheometer. The variation of molten viscoelastic behavior of FRPP with the composition, temperature, shear rate, and coupling agent are examined and discussed in this paper. Die swell phenomena of FRPP at different temperatures, shear rates, and compositions were also observed. The results were that the viscosity and modulus of FRPP increased with increasing the fiber content in FRPP. Pretreatment of glass fibers with coupling agent would enhance the interfacial adhesion between polypropylene and fibers, and the fiber length in FRPP was longer on the average. Die swell of FRPP significantly decreased by the presence of glass fibers.

Application of a modified rotary rheometer to the investigation of slurries

Abstract: A new technique for investigating some of the rheological properties of slurries is proposed. A commercial concentric cylinder viscometer was modified so that a continuous coaxial flow could be superimposed on the Couette flow; this eliminated the influence of sedimentation of the solid particles. The influence of the changed strain was measured and found to be small. Relations between the shear stress and shear rate, temperature, mass fraction of solids and particle size were determined for a coal-oil slurry. The power-law coefficients were calculated. The influence of solid particles on the power-law coefficientskm andnm was determined and approximated by empirical equations.

Shear and thermal history effects in polypropylene melts

Abstract: Fiber grade polypropylenes with melt flow indices of 3 and 12 were studied in the aspolymerized (powder) state and after pelletization. Pelletizing operations caused very little change in the molecular weight distributions of these polymers. The lower melt flow index material exhibited much greater apparent viscosity and melt elasticity in the powder than in the pellet from during screw extrusion at 190°C. These results are consistent with the existence of a higher entanglement density in the powder version. Instron rheometer data showed no difference between the two polymer forms because of the possibility for entanglement in the rheometer reservoir during rheological experiments. The effects of sample history noted with the 3 melt flow polymer were less pronounced with the lower molecular weight 12 melt flow material. The differences in flow curves of powder and pelletized forms of the latter polymer were negligible at 175 and 190°C. Differences in die swell were more noticeable, however. The effects observed are attributable to reversible shear-induced decreases in entanglement density. Similar phenomena have been reported for other polymers. The results reported here have implications in quality control procedures for thermoplastics and in the production of polymers with desired property balances.

New apparatus for simultaneous determination of phase equilibria and rheological properties of fluids at high pressures: Its application to coal pastes studies up to 773 K and 30 MPa

Abstract: In this article, we present a new apparatus based on a static method to simultaneously measure rheological properties of a dense (liquid or liquid+solid) medium and sample phases (dense and gaseous) for analysis purposes. It was especially designed to study coal pastes in the working conditions of hydroliquefaction processes. It can also be used to study other mediums such as asphalts and polymers. The rheometer part of the apparatus was already tested and results published in a previous paper. The ability of the new apparatus to get reliable vapor–liquid equilibrium data in the range of thermal stability of chemical materials is shown as a result of measurements on the nitrogen‐n‐heptane system at 497.1 K and the methane‐n‐hexadecane system at 623.1 K and comparison to literature’s data. Reproducibility tests have displayed very small data dispersion.

Dependence of flow behaviour on carbon black distribution in polyblend systems

Abstract: The flow behaviour of four blend systems was determined at four shear rates and three processing temperatures using an extrusion rheometer. The blends were based on natural rubber/polybutadiene elastomers and were prepared using various mixing sequences with the carbon black being added in different ways. The degree of die swelling was found to depend on the blending technique, the processing temperature and the extrusion rate. A theoretical model was used to calculate the stored elastic energy, shear modulus and relaxation time. Melt fracture was observed when the carbon black was premixed in just one component of the blend.

Viscosity measurement by spheres falling in a magnetic field

Abstract: A new rheometer suitable for the region of very high viscosities is presented. To measure at reasonable time and avoid degradation of the polymer, gravitational forces on iron spheres are replaced by magnetic ones. The extent of the region depends on the strength of the magnetic field available. The velocity of the falling sphere is measured by interrupting the beam of a He-Ne-Laser which is registrated by a photoresistor. Results are analysed with the help of Stokes' law for falling spheres. By measuring the magnetic forces on the sphere with a special device based on glass springs absolute values of the viscosity are obtained and liquids for calibration are not needed.

A new approach to capillary viscometry of thermoset transfer molding compounds

Abstract: A new capillary rheometer incorporated in an instrumented transfer molding press has been developed. This rheometer is effective for determining the viscosity characteristics of thermoset molding compounds under both isothermal and typical molding conditions. In examples of the rheometer's utility, the power law indices of two commercial epoxy molding compounds have been determined to be approximately 0.7. Additionally it has been shown that preconditioning typical epoxy compounds at 47 percent relative humidity causes a viscosity decrease of about 40 percent owing to plasticization of the epoxy resin.

Die-swell of antimisting kerosene: part 1. shear and normal stresses of antimisting kerosene at high shear rates determined from die-swell and torsional balance measurements

Abstract: Die-swell and torsional balance experiments were performed to measure the shear and normal stresses developed by AMK (0.3% FM-9 + glycol/amine in Jet A) and 0.1% ARCO in Jet A. Capillary tube experiments show that AMK shear thickens at a critical shear rate, reaches a maximum viscosity and then shear thins at higher shear rates. Despite the fact that the antimisting fuel made with the ARCO polymer exhibits a more conventional shear stress dependency (i.e., shear thinning), die-swell measurements indicate that both fuels develop large normal stresses at high shear rates. While the torsional balance method was able to obtain both shear and normal stress information for the ARCO polymer at high shear rates, AMK exhibited anomalous behavior that made it impractical to measure normal stresses by this method. A comparison of normal stresses for the ARCO polymer indicates that normal stresses measured by these two methods differ significantly in magnitude.

Viscometers evaluated for accurate determination of cement slurry rheology

Abstract: Choosing the proper viscometer is important because a firm handle on cement slurry rheology is essential for the design of a primary cement job. Only if slurry rheological properties are well characterized can friction pressure drops and flow regime in the annulus be predicted correctly. This is essential for optimum mud displacement and job execution. When attempting to measure slurry rheology experimentally in the laboratory, the choice of the equipment is the main problem. Two main systems are in use: pipe (capillary) rheometers and coaxial cylinder rotational viscometers. Both types of equipment feature completely different characteristics and prices. The relative advantages and drawbacks of both viscometric techniques has prompted the evaluation of 10 different rotational viscometers, and resulted in the proposal of a set of specifications representative of a good rotational viscometer suitable for measuring the rheology of cement slurries.

New Extensional Rheometer for Elongational Viscosity and Birefringence Measurements: Experimental Results and Interpretation

Abstract: This study shows that by using the recoverable strain, one can represent the elongational viscosity ηe=σe/˙e as a linear function of the quantity λr2−λr−1, characteristic of a neo-Hookian material. The elongational viscosity is then the sum of two contributions: One is related to the entropic elasticity of the chains through the recoverable deformation of the sample. The other is related to the shear viscosity at a shear rate equivalent to the extensional strain rate. In absence of a simple theoretical justification for such an equation, more experiments are being undertaken with different polymers and rubbers in order to understand how the recoverable strain is related to the chemical structure of the chain and to check the generality of the equation.

Rheological properties of coatings during drying processes

Abstract: Coatings such as paints and printing inks transferred on substrates change from viscous liquids to viscoelastic solids during drying processes and finally become a hardened film. In order to investigate more precisely the viscoelastic properties of coatings during liquid-to-solid conversion, we developed the same type of ultrasonic rheometer as employed by Mason et al., in which the reflection coefficient technique is utilized. The complex modulus can be determined by the reflection coefficient and the phase shift. Using this rheometer, we can obtain the viscoelastic properties of coatings at various stages of drying at infinitesimal shear strain at the frequency of 3 MHz. The viscoelastic properties of a commercial offset litho ink which was dried by oxidative polymerization were measured at various temperatures. From the results of viscoelastic measurements, the drying of ink seems to be accelerated remarkably with increasing temperature. As the drying processes progress, a three-dimensional network structure may be formed in the ink film with the aid of oxidative polymerization. The drying-time dependence of G′ is different from that of G″. From the drying-time dependences of G′ and G″, we can quantitatively deduce the internal structure of printing ink films during drying processes and provide a physical explanation for various drying stages. The dispersed pigments in a coating seem to play an important role in film formation and affect the mechanical properties of the drying film.

Study of polymer powder and melt rheology using a constant pressure, non‐isothermal rheometer

Abstract: A rheological analysis is proposed on a non-conventional, constant pressure, non-isothermal rheometer. The test usually starts with a polymer powder and ends with melt extrudate. The volume- (or displacement of plunger) temperature curve of the test is analyzed according to the following model: (1) at a temperature below the glass transition temperature, the test is related to the packing and/or compaction of powders, and also the compressive deformation of powders; (2) as the temperature is raised to where polymer flow begins, the test is analyzed according to melt viscous flow. The activation energy of flow of a polymer may also be estimated using this rheometer. Comparison and correlation of data using other techniques (e.g. torsional pendulum dynamic measurement, capillary rheometer, Rheometric dynamic spectrometer) will also be discussed.

Polymer Melt Rheological Property Measurement in a Novel Composite-Geometry Flow Rheometer

Abstract: A novel rheometer is described, in which extensional viscosity and elastic shear compliance are determined simultaneously from pressure measurements taken on steady state polymer melt flows through an open-ended die with successive, similarly shaped, converging and diverging zones. Equations incorporating practically realistic simplifying approximations are developed for the calculation of extensional viscosity and shear compliance from the measured pressure data. The construction of a prototype rheometer is described, and results from its operation are presented. Agreement between these results and published melt elasticity data for a low-density polyethylene material gives evidence to confirm the basic rheometric principle and flow analysis. The implications of pressure measurement errors are discussed. Assembly of the new composite-geometry rheometer in series with a conventional capillary viscometer would give in-line shear viscosity characterization simultaneously and facilitate on-line processing of...

The Use of a Modified Cone‐and‐Plate Geometry (MCP) in a Rotational Rheometer for the Measurement of Material Functions

Abstract: A “modified cone and plate” is presented as an alternative geometry for the measurement of material functions in a rotational rheometer. It gives a significant improvement in the quality of the signal for the normal force and makes it possible to reach higher shear rates prior to the point at which the sample fails. A theoretical and experimental study of this new geometry which can be used for normal force and torque measurements has been developed to obtain the first normal stress coefficient and viscosity information.