Rheological determination of peptizing agents in bentonite clays

This paper presents the results of an evaluation of the rheological properties of commercial bentonite suspensions made from peptized and unpeptized clay samples collected over a six year time span. The rheological properties of these suspensions were measured between shear rates of 5.11 to 1022 s^–1 at concentrations of 15, 30, 45, 64.2 and 70 kg/m³. Bingham, power-law and Casson models were then fitted to the shear stress and shear rate values. Parameters derived from these models were then subjected to further analyses. Four rheological methods (termed peptization index tests) were developed to differentiate between peptized and unpeptized bentonite samples.     

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 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 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 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.     

Rheological properties of skim milk gels at various temperatures; interrelation between the dynamic moduli and the relaxation modulus

The rheological properties of rennet-induced skim milk gels were determined by two methods, i.e., via stress relaxation and dynamic tests. The stress relaxation modulusG _c (t) was calculated from the dynamic moduliG andG by using a simple approximation formula and by means of a more complex procedure, via calculation of the relaxation spectrum. Either calculation method gave the same results forG _c (t). The magnitude of the relaxation modulus obtained from the stress relaxation experiments was 10% to 20% lower than that calculated from the dynamic tests.Rennet-induced skim milk gels did not show an equilibrium modulus. An increase in temperature in the range from 20° to 35 °C resulted in lower moduli at a given time scale and faster relaxation. Dynamic measurements were also performed on acid-induced skim milk gels at various temperatures andG _c (t) was calculated. The moduli of the acid-induced gels were higher than those of the rennet-induced gels and a kind of permanent network seemed to exist, also at higher temperatures. G storage shear modulus,N·m^–2; - G loss shear modulus,N·m^–2; - G _c calculated storage shear modulus,N·m^–2; - G _c calculated loss shear modulus,N·m^–2; - G _e equilibrium shear modulus,N·m^–2; - G _ec calculated equilibrium shear modulus,N·m^–2; - G(t) relaxation shear modulus,N·m^–2; - G _c (t) calculated relaxation shear modulus,N·m^–2; - G ^*(t) pseudo relaxation shear modulus,N·m^–2; - H relaxation spectrum,N·m^–2; - t time,s; - relaxation time,s; - angular frequency, rad·s^–1. Partly presented at the Conference on Rheology of Food, Pharmaceutical and Biological Materials, Warwick, UK, September 13–15, 1989 [33].     

Incipient behaviour of gelatin gels

The present work describes isothermal (25°C) gelation measurements for gelatin gels over a range of concentrations. Methods for the estimation of the gel time are discussed, and data compared with two recent models. The isothermal time growth of modulus is also investigated, and the superposition of such data discussed. For concentrations close to the critical gel concentration C ₀ there are significant deviations in the latter case. These may be related to the approach to the biphasic region of the phase diagram suggested by other workers.     

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 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.     

Relaxation dynamics of selected polymer chain segments and comparison with theoretical models

Simultaneous measurement of infrared dichroism and birefringence is used to study selected polymer segment dynamics in isotopically labeled block copolymers. Two different polymers were studied: polybutadiene and poly (ethylene propylene). The first type consisted of a triblock with a short middle block labeled and a diblock with a short end block labeled, while the second type consisted of a triblock with three equal blocks and the end blocks labeled. Results of step strain experiments at –10°C for polybutadiene and at room temperature for poly(ethylene propylene) indicated that segments located at chain ends relax faster than segments located at chain centers. These experimental data were compared to the predictions of two molecular models: the bead-spring model of Rouse and the tube model of Doi and Edwards, and it was found that both models correctly predict the qualitative features of segmental relaxation. However, the tube-model predictions were closer to the experimental results. In addition, when the effects of orientational coupling interactions between segments in the melt were incorporated into this model, its predictions quantitatively agreed with the experimental results. The orientational coupling coefficient for poly(ethylene propylene) was 0.45 as measured from previous work, and for polybutadiene it was found to be 0.4.Delivered as a Keynote Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.Dedicated to Prof. R.S. Stein, University of Massachussets at Amherst, USA, on the occasion of his 65th birthday.     

A method for correction of the wall-slip effect in a Couette rheometer

A simple method for correction of the wall-slip effect in a Couette rheometer was derived. The method requires only two series of measurements (two flow curves) performed in two measuring sets of any dimensions, and therefore it may be applied for the results obtained in each rheometer with a standard cup and bob set. The method was checked for experimental data and also verified theoretically for a hypothetical liquid. H height of cylinder - M torque - r distance from axis - R _i ,R ₀ radius of inner and outer cylinder - R _m average radius defined by Eq. (7) - u slip velocity - shear rate - shear rate for no-slip conditions - Newtonian viscosity - angular speed - angular speed of the rotating cylinder     

In situ technique for monitoring the gelation of UV curable polymers

Ultraviolet-radiation-cured cross-linked systems are used extensively in optoelectronic applications. We describe a new in situ technique for doing controlled curing of photosensitive materials and monitoring the gelation through dynamic theological measurements. In this method, a sample placed between quartz windows of a modified parallel plate fixture of a Rheometrics Mechanical Spectrometer is radiated from a collimated UV source using a liquid light guide and a mirror. By varying the sample exposure to UV radiation, the degree of cross-linking can be precisely controlled to observe the material behavior in the pre, post, and critical gel state. Time-dependent measurements on urethane based materials show the gelation behavior to have an induction period with no change in dynamic moduli (G, G), followed by their sharp increase as the materials develop a network structure. The critical gel point is characterized by a power-law dependence of the dynamic moduli on frequency. The gelation kinetics scales with sample thickness and radiation intensity, the scaling factor in both cases being the critical gelation time. The rheological measurements correlate with differential photocalorimetric studies.     

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 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.     

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.     

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.     

A novel geometry for rheological characterization of viscoelastic materials

A novel geometry for generating a viscometric flow presents advantages of both cone and plate and parallel plate geometries, regarding uniform shear field and adjustable range of measurement. Kinematics and dynamics of the generated flow have been described mathematically utilizing an orthogonal curvilinear coordinate system based on the shapes of the shearing surfaces which are similar to the surface that generates the flow. Simple equations that allow the calculation of quantities of experimental interest in the rheological characterization of liquid materials, namely, shear rate, shear stress and two normal stress differences, have also been derived.The geometry, called pseudosphere, was tested with two types of fluids (Newtonian and pseudoplastic). Results show that the geometry can be used with low viscosity liquids (Newtonian liquids) by only adjusting the gapH. The behavior of pseudoplastic fluids for both low and moderately high viscosity could also be studied with this geometry. Very reproducible results were obtained when compared with those obtained with cone and plate geometry. Regions of lower shear rate could be studied using only the pseudosphere geometry.     

The evolution of linear viscoelasticity during the vulcanization of polyethylene

The evolution of linear viscoelasticity during the vulcanization of polyethylene is studied through the gel point. The material in the vicinity of the gel point is described by two scaling laws: one characterizes the viscoelasticity at the critical point and a second characterizes the evolution of viscoelasticity near the gel point. Time Resolved Mechanical Spectroscopy is used to observe both scaling phenomena. The material at the gel point displays power law relaxation over five decades of time with a power-law relaxation exponent equal to 0.32. This study conforms with previous findings that this exponent is composition-dependent. The longest relaxation time diverges in the vicinity of the gel point as _max |p _c - p| ^–1/, and we find = 0.2. This result conforms with previous reports that this exponent may be independent of composition. The Arrhenius flow activation energy for this material undergoes three-fold changes during crosslinking up to the gel point. A single-adjustable-parameter stretched-exponential-power law relaxation function is an inadequate representation of crosslinked materials over any significant range of extent of the reaction up to the gel point.     

Evolution of viscoelastic properties of polyurethane in the course of curing

Simultaneous measurements of the components of dynamic modulus at the set of frequencies were made by Fourier-Transform Mechanical Spectroscopy (FTMS) to investigate the curing process of a segmented polyurethane.The whole process of curing is treated as consisting of three stages. In the first stage, the material can flow and this stage is complete at the gel-point. In the second stage, the curing proceeds in the network and ends with phase separation of aggregating segments (blocks) of polymeric chains. In the third stage, the curing continues in the two-phase system. The object of investigation was the transition from the second to the third stage. It was shown that the position of the maximum of loss tangent depends on frequency and does not coincide with different characteristic points marking the time dependencies of G and G. This is due to the formation of micro-particles of the newly formed phase. The FTMS method is used for separation of the modulus changes into parts related to formation of chemical and physical networks.Special means of treating calorimetric measurements identified a weak maximum heat output at the moment corresponding to the transition point.