Flow behavior of polyacrylamide solution. III. Mathematical treatment

The flow behavior of polyacrylamide solutions was systematically determined over a wide range of temperatures (20–50°C) and concentrations (20–50 ppm) by using a coaxial cylinder viscometer. The results indicated that the rheological behavior of low-concentration polyacrylamide solution behaves similar to non-Newtonian fluids at all these concentrations. The effect of temperature on the consistency coefficient and flow behavior index of polyacrylamide solution of the different concentrations followed an Arrhenius-type relationship. Moreover, the effect of concentration on consistency coefficient and flow behavior index followed an exponential-law relationship at the temperatures used. The rheological constants for the Arrhenius and exponential-law models were determined. The combined effect of temperature and concentration on the coefficient of dynamic shear stress can be represented by a single equation: shear stress = 2.446 × 10⁻⁷exp(0.0639C + 3613/RT)(shear rate)^{2.337 exp(−0.00707C−245/RT)}. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2784–2789, 2001     

Rheological properties of aqueous polyacrylamide/NaCl solutions

Rheological properties of aqueous polyacrylamide‐sodium chloride solutions are studied using RheoStress RS100. Polyacrylamide concentration was varied from 0.25 to 1.0% by weight, whereas sodium chloride ranged from 0.0 to 10 g L⁻¹. This range of concentrations is suitable to study many of the polyacrylamide‐sodium chloride rheological properties. Steady flow parameters, yield stress, thixotropic behavior, creep recovery, and dynamic tests are covered in this study. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1905–1912, 1999     

Rheological properties of carboxymethyl cellulose

This work is a complete and comprehensive study of the rheological properties of carboxymethyl cellulose (CMC) solutions. The study was carried out using the computer controlled RheoStress RS100 system of Haake. CMC concentration in the test solutions ranged by weight from 1 to 5%. This range was sufficiently wide to reveal the nearly Newtonian behavior at the lower end of concentrations, and the definitely pseudoplastic, thixotropic, and viscoelastic behaviors of CMC solutions at the higher end of concentrations. The scope of the study included measurements of steady-state parameters, transient shear stress response, and yield stress. In addition, the thixotropic, creep recovery, and dynamic responses of solutions with high concentrations were measured. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 289–301, 1997     

Study on the properties of magnetorheological gel based on polyurethane

Magnetorheological gels (MRGs) known as a new kind of magnetorheological material are composite gels containing magnetic particles suspended in polymer gels. In this study, a category of MR polymer gels based on polyurethane (PU) were prepared. The microstructures of these MRGs were observed with a digital microscope. Their rheological properties under both steady shear and oscillation testing were characterized by using a MR rheometer. The viscosity of the PU MRG decreased with the increment of NCO/OH ratio and increased with the increment of the weight concentration of carbonyl iron particles, molecular mass of poly propylene glycol, and applied magnetic field. The storage modulus increased gradually with the increment of applied magnetic field and weight concentration of carbonyl iron particles. The PU MRG exhibits high static shear yield stress (60.8 kPa, at 573 mT) and dynamic shear yield stress (83.9 kPa, at 573 mT) and wide variation range (static shear yield stress: 6–62 kPa, dynamic shear yield stress: 15–85 kPa). These advantages indicate that PU MRG is able to satisfy wide applications. In addition, both static and dynamic shear yield stresses of the MRG samples increase with the increment of molar mass of polypropylene glycol. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Measurement of the rheological properties of thermoplastic elastomers

Using the Han slit/capillary rheometer, measurements were taken of the rheological properties of commercially available thermoplastic elastomers, namely, styrene–butadiene–styrene (SBS) block copolymer (Shell, Kraton), ethylene–propylene copolymer (Exxon, Vista), olefinic-type thermoplastic rubbers (UniRoyal, TPR 1600, TPR 1900, and TPR 2800), and urethane thermoplastic elastomers (UniRoyal, Roylar A863 and Roylar E9). The rheological properties determined were shear viscosity and first normal stress difference at various melt temperatures. Depending on the material and the melt temperature tested, the range of shear rates tested was 50 to 700 sec^?1, and the range of shear stresses tested was 10⁵ to 10⁶ dyn/cm². For comparison purposes, rheological measurements were also taken for a few materials using the Weissenberg rheogoniometer although its use was limited to low shear rates (or shear stresses). It was demonstrated clearly that the Han slit/capillary rheometer is a unique instrument for determining the rheological properties of thermoplastic elastomers in the range of high shear rates (or high shear stresses) often encountered in various polymer processing operations.     

Viscoelasticity of concentrated polyacrylonitrile solutions: effects of solution composition and temperature

The effects of solution composition and temperature on the viscoelasticity of concentrated polyacrylonitrile (PAN) solutions were studied using a variety of rheological measurements, such as steady‐state shearing, dynamic stress sweep and transient rheological tests. The first normal stress difference N₁ and the shear stress τ were found to increase with decreasing temperature and increasing PAN concentration and water content in the solutions. The crossover point of N₁ and τ, denoting the equal contribution of viscosity and elasticity to the viscoelasticity of the solutions, moved to lower shear rates at lower temperature, higher PAN concentration and higher water content. The values of the relaxation time (λ) were larger at 70 °C than at 40 °C. In addition, the changes of λ with PAN concentration and water content were different at the two temperatures, ascribed to the different states of the solutions. The PAN solutions were in the linear viscoelastic regime in the temperature range 40–70 °C when the shear stress was below 300 Pa. The creep compliance recovery rate decreased with increasing temperature, but increased with increasing PAN concentration and water content. Thixotropic tests showed that the thixotropy of the solutions was also affected by the solution composition and temperature. Gelation was found to influence the way the solution composition and temperature affected the viscoelastic properties of the PAN solutions. Copyright © 2011 Society of Chemical Industry     

An experimental study of the relationship between rheological properties and spinnability in the dry spinning of cellulose acetate–acetone solutions

The elastic and viscous properties of five cellulose acetate–acetone solutions, varying from 19.9% to 28.6% solids concentration, are independently determined at 60°C by capillary rheometry techniques. The viscous flow behavior of the solutions is determined over four decades of shear rate. The Bagley analysis is used to determine the entrance pressure drop and the true shear stress at various shear rates. A plot of the entrance pressure drop at the maximum experimental shear rate versus solution concentration undergoes a rapid increase in slope at 24.0% solids concentration, the significance of which is discussed with respect to the development of an elastically deformable chain entanglement network. The die swell behavior of the solutions at 60°C is determined on a commercial-type dry-spinning apparatus. When the die swell ratio is plotted versus volumetric flow rate, all five solutions are found to possess a characteristic curve with a distinct maximum. Photographs illustrating the variation of die swell with volumetric flow rate are shown. Die swell measurements are also shown to correlate well with entrance pressure drop measurements. The degree of spinnability of each cellulose acetate–acetone solution at 60°C is found by determining first godet speed at which one or more threads break abruptly. Spinnability is found to go through a maximum at 24.0% solids concentration. The rheological measurements and spinnability results are discussed through the aid of a single rheological parameter incorporating both elastic and viscous solution responses.     

Characterization of the rheological behavior of UHMWPE gels using parallel plate rheometry

The effects of shear flow, temperature, and gel concentration on the rheological behavior of the ultrahigh-molecular-weight polyethylene (UHMWPE) gel in gel spinning process were investigated. The gel point was determined using parallel plate rheometry in rotation mode with controlled stress. Likewise, the flow curves at various temperatures were determined with controlled shear rate from 10⁻² to 10 s⁻¹. Whereas the shear storage modulus (G′) was obtained in oscillation mode with controlled strain from 1 to 100%. The result shows that the gel point of the UHMWPE gel increases with increasing gel concentration. The result from the strain sweep indicates that G′ of the gel is 1.5 × 10³ Pa, and it exhibits a plateau at low strain, but it is reduced with increasing strain. At low shear rates, for temperatures above gel point, all flow curves exhibit a plateau, then go down with increasing shear rate. Studying contributions from UHMWPE gel concentration, temperature, and shear rate for rheological view, we found that spinning at 6% UHMWPE (MW : 1.4 × 10⁶ g/mol) gel and 140°C gives the best effect on formation of fiber structure. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1009–1016, 1998     

PREPARATION AND CHARACTERIZATION OF BIODEGRADABLE POLYMER MUD BASED ON MILLET STARCH

A biodegradable polymer mud was prepared using Millet starch pre-gelatinized in the absence of a solvent. The filtration and rheological properties of the mud were studied at 25°–200°C temperature range and at 0.01–0.05 g/mL concentration of starch using filter loss and viscometric methods respectively. Experimental results showed that the new mud has better filtration control behavior and thermal stability at all the temperatures than widely used mud prepared with hydroxy propyl–modified starch. The mud displayed thermal degradation at 200°C. The values of flow index were found to be less than 1.0, showing non-Newtonian and pseudoplastic flow behavior of the mud. Shear stress and yield stress increase with increase in concentration. Viscosity decreases with increasing shear rate, showing shear thinning behavior of the mud. The polymer mud obeyed Henri Darcy and API models for static filtration as well as power law and Herschel-Bulkley models for fluid rheology. The new mud is purer and more suitable for drilling operations in environmentally sensitive areas than the widely used mud.     

Rheological characterization of cellulose solutions in N‐methyl morpholine N‐oxide monohydrate

Three different modes of rheological properties were measured on 11 and 13 wt % solutions of cellulose in N‐methyl morpholine N‐oxide (NMMO) monohydrate, in which concentration range lyocell fibers of much reduced fibrillation are preferably produced. The dynamic rheological responses revealed that the Cox–Merz rule did not hold for these cellulose solutions. Both cellulose solutions showed a shear thinning behavior over the shear rate measured at 85, 95, 105, and 115°C. However, 13 wt % solution gave rise to yield behavior at 85ºC. The power law index ranged from 0.36 to 0.58. First normal stress difference (N₁) was increased with lowering temperature and with increasing concentration as expected. Plotting N₁ vs shear stress (τ_ω) gave almost a master curve independent of temperature and concentration, whose slope was about 0.93 for both cellulose solutions over the shear rate range observed (τ_ω > 500 Pa). In addition, the cellulose solutions gave high values of recoverable shear strain (S_R), ranging from 60 to 100. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 216–222, 2002     

A Survey of Rheological Properties of One-Component Epoxy Adhesives

Flow characteristics of seven commercially available one-component epoxy adhesive pastes were measured using a controlled shear stress rheometer and a controlled shear rate rheometer over a temperature range from 5°C to 60°C. Combining data obtained from both controlled rate and controlled stress experiments over a wide range of shear rates, we observed Newtonian flow (shear stress proportional to shear rate) at very low shear rates, a plateau “shear thinning” region at intermediate shear rates, and a second region of linear dependence of shear stress on shear rate at high shear rates. The adhesive pastes exhibited a very broad range of rheological behavior. Two flow parameters important to adhesive application technology, the plastic viscosity and the apparent yield stress, were measured for each adhesive. The plastic viscosity ranged from 11.6 to 329.5 Pa. s; the apparent yield stress ranged from 56.2 to 413 Pa. The temperature dependence of the rheological parameters of the epoxy adhesive pastes was also determined. The results are reported as the activation energies, E_η and E_σ , of plastic viscosity and apparent yield stress, respectively. The apparent yield stress of each adhesive paste was much less sensitive to changes in temperature than was the plastic viscosity. This suggests that the processing characteristics are likely to show qualitative as well as quantitative changes with temperature.     

The Rheological Behavior of Salt Tolerant Polyacrylamide Solutions

The rheological behavior of viscoelastic fluids was investigated with regard to the specialty of tertiary oil recovery. Aqueous polyacrylamide solutions at different concentrations were selected to simulate viscoelastic polymer systems, and the Haake RS 150 type rheometer was used to measure the rheological behavior. The experimental results showed that the viscoelasticity was positively influenced by polyacrylamide solution concentrations and negatively affected by solution temperatures. The coefficient of first normal stress deference decreased with increasing shear rate. In addition, the relationship between viscosity and the coefficient of first normal stress with shear rate obeyed a power law model. The viscosity decreased with increasing metal ion concentration and time.     

Rheological properties of high concentrations of carboxymethyl cellulose solutions

The study was concerned with measurements of steady‐state parameters, the transient shear stress response, and the yield stress of carboxymethyl cellulose (CMC) solutions at high concentrations. Tests also included thixotropic and viscoelastic behavior and dynamic responses. The concentrations ranged by weight from 5 to 8% of CMC. The steady‐state shear flow showed that at higher shear rates the viscosities of CMC solutions tend to be less dependent on the concentration. The solutions showed rheopectic behavior for very small shear rates. No yield stress was detected. Measurements recorded the thixotropic behavior. At higher stress values, nonlinear viscoelastic effects were detected. Dynamic viscosities measured in a dynamic test were higher than were the shear viscosities at the same concentrations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1787–1801, 2001     

Rheological and drug‐release behaviour of a scleroglucan gel matrix at different drug loadings

The aim of this study was to investigate the drug‐loading effects on release and mechanical properties of a scleroglucan gel, with the intention of considering them in delivery systems formulations. The rheological and kinetic properties of a 2 % w/w scleroglucan gel matrix loaded with 0, 0.02, 0.04, 0.06, 0.2 and 0.4 % w/w of theophylline (Th, used as a model drug) were investigated. Rheological measurements were performed in a controlled‐stress rotational‐shear rheometer under isothermal conditions. For theophylline release from the gel a flat Franz cell was used and the kinetic parameters were derived applying a semi‐empirical power law. The influence of scleroglucan molar weight on kinetic and rheological behaviour was also studied. Results suggest two possible effects of drug loading on the gel network: in the 0.04–0.06 % w/w Th range a plasticizing effect and in the 0.2–0.4 % w/w Th range a rigidization effect. In the first range mentioned, the changes in the gel structural properties tested by means of rheological measurements are coincident with changes in drug‐release kinetics. Copyright © 2005 Society of Chemical Industry     

In-line fiber-optic near-infrared spectroscopy: Monitoring of rheological properties in an extrusion process. Part II.

In an extrusion process, linear viscoelastic properties of molten poly(ethylene vinyl acetate) (EVA) copolymers, which have one principal factor of variation, can be estimated from in-line near-infrared (NIR) spectra. The NIR transmission spectra of molten polymer flow stream were collected in a flow cell attached to a single-screw extruder. Dynamic rheological functions obtained from linear viscoelastic measurements, for example, the complex viscosity response, are regressed against the NIR spectra. The primary method for the rheological measurements involved sinusoidal, oscillatory shear experiments at varying angular frequencies using a cone-and-plate viscometer. All measurements were carried out on molten EVA polymers at 200°C. Calibration models were built on spectra in the carbon—hydrogen (C—H) vibrational stretch, first overtone, wavelength region (1620–1840 nm), and these models were used to predict the rheological material functions of copolymer samples. The robustness of these models was tested on independent prediction samples that had not been included in the calibration models. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68 :873–889, 1998     

MELT RHEOLOGICAL PROPERTIES OF TALC-FILLED ISOTACTIC POLYPROPYLENE COMPOSITES

The melt rheological properties of talc-filled isotactic polypropylene have been studied at talc concentrations of 0–33.3 vol% and at 493 K. The composites followed a power law model in the shear stress–shear rate dependence and were shear thinning. The apparent melt viscosity increased whereas the melt elasticity parameter “first normal stress difference” decreased as the talc concentration increased. Surface modification of the talc by a coupling agent LICA 38 modified the rheological properties through bonding and/or a plasticizing/lubricating effect.     

Evaluate the nonlinear viscoelasticity of polyolefin melts using the Larson model

Nonlinear rheological properties of polyolefins have long been studied and predicted by using the Larson model with the damping function generally obtained from the stress relaxation measurements. In this study, we investigate the nonlinear rheological properties of high density polyethylene (HDPE) and polypropylene (PP) using the Larson model with damping functions obtained from either the dynamic frequency sweep or the stress relaxation test. Experimental measurements and their corresponding model predictions for the rheological parameters were then compared to evaluate the applicability of the Larson model to the nonlinear rheology, and the following conclusions could be achieved. The steady shear viscosity could be satisfactorily described by the Larson model with the damping functions obtained from the two different methods, except at shear rates higher than 10³ s^?1. The predicted first normal stresses also account for the measured data, except for those using the stress relaxation data showing a little deviation for the PP sample. In addition, the predictions for elongation viscosity are also in good agreement with the experimental results within the short range of elongation rate achieved in this work. POLYM. ENG. SCI., 54:2354–2361, 2014. © 2013 Society of Plastics Engineers     

A study of the uptake and gelation reactions of Cr(III) oligomers with polyacrylamide

The reaction rates of Cr(III) oligomers with partially hydrolyzed (PAAm) polyacrylamide were measured. The oligomers were prepared in relatively pure form using liquid chromatography, allowed to react with polymer, quenched, and then separated using equilibrium dialysis. In the pH range of 4–5, Cr(III) concentrations in the range of 8–30 ppm and polymer concentrations in the range of 4000–20,000 ppm, reaction rates increased with increasing oligomer size, concentration, and pH. Gelation rates determined using rheological measurements were found to follow closely the Cr(III) reaction rates. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1381–1391, 1997     

Rheological behavior of hydrophilic silica dispersion in polyethylene glycol

The rheological properties of hydrophilic fumed silica dispersed in polyethylene glycol (PEG) were investigated. The dispersion was prepared by dispersing the fumed silica in PEG with various concentrations. The reversible sol–gel transition was observed over 5 wt % of silica concentration as a function of temperature. The gelation temperature was found to depend on the applied shear stress and silica concentration, and the high shear stress was found to lead to the decrease of sol–gel transition temperature of the dispersion with the same silica concentration. As the silica concentration increases, the sol–gel transition shifts to the lower temperature. © 2006 Wiley Periodicals, Inc. J Apple Polly Sci 103: 2481–2486, 2007     

Irregularities in steady flow for non-newtonian fluids between cone and plate

Flow irregularities have been visually observed in solutions of polyacrylamide of high molecular weight on shear in a cone-and-plate rheometry (gap angle 2.3°). This anomalous flow was found to depend on molecular weight, concentration, and solvent. The onset of flow irregularities were generally at shear rates < 5 sec^?1. A dimensional analysis shows that the elastic component of the fluid is responsible for the anomalous flow. The onset of flow irregularities has been predicted from measurements of recoverable strain as a function of shear stress.