Rheometric Measurements Research Articles

Comparing inline extrusion viscosity for different operating conditions to offline capillary viscosity measurements

AbstractDegermed, dehulled cornmeal grits were extruded through a self‐heating single screw extruder with inner restrictions. Constant degree of screw fill was tested at 32.5, 35, and 37.5% w.b. moisture content. The screw speeds tested were 100, 200, and 300 rpm. A novel two hole die was used and showed the melt viscosity to decrease with increased screw speed. The inline data was compared to offline capillary rheometer measurements and showed a decrease in melt viscosity. For example, at 35% moisture content and roughly 110°C the melt viscosity decreased by 32% from offline to 100 rpm for a shear rate of 100 s−1. The melt viscosity change suggested that each process transforms the material differently into two different materials which was supported by RVA pasting profiles. The extruder die temperature increased with increased screw speed and decreased with increased moisture content. The melt viscosity behaved nonlinearly with moisture content due to high temperature rise and starch degradation. The flow behavior index increased with increased screw speed. Overall, the novel two hole die showed general trends of the melt viscosity behavior with operating conditions and made comparisons to offline data.Practical ApplicationsThe extrusion process is an efficient process that can produce a wide range of products at various throughputs depending upon operating conditions and extruder design. Originally developed for the plastics industry, extrusion has been applied to food and pharmaceutical applications. This application comes with increased challenges due to heterogeneous materials that consist of biological macromolecules that are Non‐Newtonian in rheological behavior as well as being susceptible to temperature and shear degradation. The product rheological properties are dependent on extruder design and operating conditions. Unfortunately, measuring the viscosity while extruding can be complicated, time consuming, and expensive. Thus, to facilitate the design of effective future extruders, the viscosity behavior must be able to be predicted from an offline method which is more cost and time effective.

Use of bending beam rheometer test for rheological analysis of asphalt emulsion-cement mastics in cold in-place recycling

This paper focused on exploiting the potential of the bending beam rheometer (BBR) test for analyzing asphalt emulsion-cement (AEC) mastics tailored for cold in-place recycling applications in the first weeks of curing, i.e. phase which implies the coexistence of viscoelastic and brittle materials. A consistent modified BBR testing protocol, which includes the experimental solutions devised for the practical execution of these unconventional rheometric measurements (sample preparation and test procedure), was proposed. The authors suggested to introduce glass microspheres, acting as “inert solid skeleton”, in the production of AEC mastics for BBR prismatic beams, to study the interaction between asphalt emulsion and cement in thin film and to limit the specimens’ shrinkage and warpage during the curing period. Finally, a feasibility study for validating the new modified experimental setup was presented, highlighting, with an explanatory overview of the types of results that can be expected, the macroscopic behaviors of some AEC mastics as a function of different parameters (asphalt binder to cement ratio, curing time and temperature).

Natural Rubber Composites Filled with Crop Residues as an Alternative to Vulcanizates with Common Fillers.

This present study is focused on exploring the possibility of using agricultural waste in the form of cereal straw as an active filler of biocomposites. The effect of lignocellulosic filler addition on the multifunctional properties of natural rubber composites was investigated. The results were compared with the properties of vulcanizates containing commonly used reinforcements in elastomer technology (carbon black, silica, chalk, talc). Rubber mixtures filled with straw showed the highest torque increase during rheometric measurements, which indirectly indicated a high degree of crosslinking and hardness of composites. It was found that the effect of straw addition on vulcanization time of elastomer blends was comparable with the results obtained for other conventional fillers. Moreover, the results confirmed that novel composites based on natural rubber filled with crop residues were attractive materials owing to their capacity for the formation of “structure” in combination with a good impact on reinforcement. Vulcanizates with the addition of straw showed the best barrier properties and resistance to thermo-oxidative aging from all tested samples. Furthermore, straw-based composites demonstrated that cereal straw waste could be used as an alternative, biodegradable and eco-friendly reinforcement of natural rubber composites.

Nonlinear viscoelastic properties of native male human skin and in vitro 3D reconstructed skin models under LAOS stress

This work discusses the first set of rheometric measurements carried out on commercially accessible juvenile and aged skin models under large amplitude oscillatory shear deformations. The results were compared with those of native male whole human and dermis-only foreskin specimens, catering to a few ages from 0.5 to 68 years, including specimens from a 23-year-old male abdomen. At large strains, strain thinning was more pronounced for the dermis of the young skins and for their whole skin counterparts. An inverse qualitative tendency was observed for the adult skins and the skin models. This can be explained by the high dermal collagen compactness associated with an incomplete epidermal proliferation. The qualitative Lissajous plots as well as the quantitative dimensionless indices analyzed using the MITlaos software indicated predominant nonlinear intracycle elastic strain stiffening and viscous shear thinning for all the native specimens at the maximum deformation. For the full thickness models, we have evidence of structure collapse and yielding under similar conditions. The whole skin specimen from the 68-year-old male showed smaller age-dependent nonlinear elastic contributions than the dermis, which we relate to the epidermal degeneration taking place during aging. Regardless of the age group, the models manifested more pronounced intercycle and intracycle elastic nonlinearities, and their magnitudes were significantly larger. The nonlinear elastic trends will serve as advanced standards for understanding and delineating the mechanical limits of destructive and non-destructive deformations of such unique biomaterials.

A simulation-based approach to evaluate objective material parameters from concrete rheometer measurements

AbstractModern concretes such as ultra-high performance concrete (UHPC) show excellent strength properties combined with favorable flow properties. However, the flow properties depend strongly on process parameters during production (temperature, humidity etc.), but also change sensitively even with slight variations in the mixture. In order to ensure desired processing of the fluidlike material and consistent process quality, the flow properties of the concrete must be evaluated quantitatively and objectively. The usual evaluation of measurements from concrete rheometers, for example of the ball probe system type, does not allow the direct determination of the objective material parameters yield stress and plastic viscosity of the sample. We developed a simulation-based method for the evaluation of rheometric measurements of fine grained high performance concretes like self-compacting concrete (SCC) and UHPC. The method is based on a dimensional analysis for ball measuring systems. Through numerical parameter studies we were able to describe the identified relationship between measuring quantities and material parameters quantitatively for two devices of this type. The evaluation method is based on the Bingham model. With this method it is possible to measure both the yield stress and the plastic viscosity of the fresh sample simultaneously. Device independence of the evaluation process is proven and an application to fiber-reinforced UHPC is presented.

A simulation-based approach to evaluate objective material parameters from concrete rheometer measurements

A simulation-based approach to evaluate objective material parameters from concrete rheometer measurements

Prediction of the swelling capacity of salt-insensitive superabsorbent polymers in concrete by rheological measurements

A study on the macroscopic viscosity of a flowable, fine-grained high-strength mortar was conducted in order to estimate the swelling capacity of two salt-insensitive superabsorbent polymers (SAPs). In doing so, rotational rheometer measurements of the mortar modified with dry pre-mixed SAP were performed at several water-to-cement ratios (W/C), i.e. in the range 0.32 to 0.40. The swelling capacity of each SAP was estimated by correlating the fitted macroscopic viscosity vs. solid particle fraction curve with the curve of the plain mortar without addition of SAP, produced at the same W/C. The swelling capacities were found to yield 28 g pore water per g dry SAP (g/g) and 35 g/g, respectively. In addition to this new approach, two more practical relevant test methods were evaluated with respect to swelling capacity: first, comparative mortar spread tests, which were based on the use of the same fresh mortars but with less amount of superplasticizer, and second, tea bag tests with plain SAP immersed in an artificial pore solution. Only minor differences were found for the estimated swelling capacities. Hence the conclusion may be drawn that all three test methods are suitable for determining the swelling capacity of SAP in a cementitious environment.

Flow analyses of highly concentrated xhantan gum fluid

The concentration effect of Xanthan gum (XG) solutions (1.0, 1.5, 2.0, 2.5% w/v) on the rheological flow parameters are examined using stress controlled rheometer and gravity driven flow set-up measurement at 25°C. Concentrated XG solutions has yielding behavior obtained by fitting results through Herschel-Bulkley (HB) model with highest regression coefficient R2 = 0.995 and R2 = 0.993 respectively by rheometer and set-up measurement. The results agreed well each other from these measurements. Increasing the concentration of XG solutions promote dynamic and static yield stresses due to increase of entanglement structure density of XG solutions. Also, the magnitudes of consistency index, K, have increasing trend with XG concentration as a result of increasing entanglement density of XG structure. Static yield stress values are much closely dynamic stress values getting from under gravity dynamic flow indicating that supplies undisturbed moleculer structure of XG due to nature of creeping flow.

Polymer Injectivity: Investigation of Mechanical Degradation of Enhanced Oil Recovery Polymers Using In-Situ Rheology

Water soluble polymers have attracted increasing interest in enhanced oil recovery (EOR) processes, especially polymer flooding. Despite the fact that the flow of polymer in porous medium has been a research subject for many decades with numerous publications, there are still some research areas that need progress. The prediction of polymer injectivity remains elusive. Polymers with similar shear viscosity might have different in-situ rheological behaviors and may be exposed to different degrees of mechanical degradation. Hence, determining polymer in-situ rheological behavior is of great significance for defining its utility. In this study, an investigation of rheological properties and mechanical degradation of different partially hydrolyzed polyacrylamide (HPAM) polymers was performed using Bentheimer sandstone outcrop cores. The results show that HPAM in-situ rheology is different from bulk rheology measured by a rheometer. Specifically, shear thickening behavior occurs at high rates, and near-Newtonian behavior is measured at low rates in porous media. This deviates strongly from the rheometer measurements. Polymer molecular weight and concentration influence its viscoelasticity and subsequently its flow characteristics in porous media. Exposure to mechanical degradation by flow at high rate through porous media leads to significant reduction in shear thickening and thereby improved injectivity. More importantly, the degraded polymer maintained in-situ viscosity at low flow rates indicating that improved injectivity can be achieved without compromising viscosity at reservoir flow rates. This is explained by a reduction in viscoelasticity. Mechanical degradation also leads to reduced residual resistance factor (RRF), especially for high polymer concentrations. For some of the polymer injections, successive degradation (increased degradation with transport length in porous media) was observed. The results presented here may be used to optimize polymer injectivity.

Shear thinning in non-Brownian suspensions explained by variable friction between particles

We propose to explain shear-thinning behaviour observed in most concentrated non-Brownian suspensions by variable friction between particles. Considering the low magnitude of the forces experienced by the particles of suspensions under shear flow, it is first argued that rough particles come into solid contact through one or a few asperities. In such a few-asperity elastic–plastic contact, the friction coefficient is expected not to be constant but to decrease with increasing normal load. Simulations based on the force coupling method and including such a load-dependent friction coefficient are performed for various particle volume fractions. The results of the numerical simulations are compared to viscosity measurements carried out on suspensions of polystyrene particles ($40~\unicode[STIX]{x03BC}\text{m}$in diameter) dispersed in a Newtonian silicon oil. The agreement is shown to be satisfactory. Furthermore, the comparison between the simulations conducted either with a constant or a load-dependent friction coefficient provides a model for the shear-thinning viscosity. In this model the effective friction coefficient$\unicode[STIX]{x1D707}^{eff}$is specified by the effective normal contact force which is simply proportional to the bulk shear stress. As the shear stress increases,$\unicode[STIX]{x1D707}^{eff}$decreases and the jamming volume fraction increases, leading to the reduction of the viscosity. Finally, using this model, we show that it is possible to evaluate the microscopic friction coefficient for each applied shear stress from the rheometric measurements.

Investigation of the Effect of Filler Concentration on the Flow Characteristics of Filled Polyethylene Melts

Abstract All polymeric slurries that have a high concentration of filler are shear thinning. Shear thinning is an important characteristic of polymers, filled and unfilled, because it enables an increase in the throughput, shear rate in a die or an injection molding system without having to use substantially more power to increase the flow rate. Newtonian fluid-based slurries show an increase in shear thinning as the concentration of “filler” increases above the percolation threshold. As particle maximum packing concentration is approached the slurries begin to approach a perfect pseudoplastic fluid. In some cases, the shear thinning characteristics of a filled polymer do not increase substantially as the filler loading is increased. This is a quite different response than in Newtonian fluid-based slurry. Therefore, it is important to understand the materials engineering interactions that control shear thinning so that process flow models can better predict the performance of filled polymer systems. Highly filled polymers can have processing issues, including high screw shaft torque, energy consumption, die pressure and melt temperature rise. Previous theoretical developments and experimental evaluations of highly filled polymer melts showed that the rheology can be effectively described with a percolation model. In this work, capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide fillers are reported using percolation theory concepts. The theoretical treatment of the rheology as a particulate percolating system with power-law behavior is used to analyze capillary rheometer data. The observed effects of resin molecular weight, filler type and size on rheology are described. Engineers that design and debottleneck polymer processes need to utilize the polymer viscosity at the minimum process shear rate to determine the smallest motor that will allow the process to run; in addition, the shear thinning characteristics of the polymer are used to indicate how much increased production may be possible with a given motor size. Thus, some examples of expected effects on melt processing are also presented.

Synergistic Effects of Bitumen Plasticization and Microwave Treatment on Short-Term Devulcanization of Ground Tire Rubber.

Ground tire rubber (GTR) was mechano-chemically modified with road bitumen 160/220 and subsequently treated using a microwave radiation. The combined impact of bitumen 160/220 content and microwave treatment on short-term devulcanization of GTR was studied by thermal camera, wavelength dispersive X-ray fluorescence spectrometry (WD-XRF), static headspace, and gas chromatography-mass spectrometry (SHS-GC-MS), thermogravimetric analysis combined with Fourier transform infrared spectroscopy (TGA-FTIR), oscillating disc rheometer and static mechanical properties measurements. The obtained results showed that bitumen plasticizer prevents oxidation of GTR during microwave treatment and simultaneously improves processing and thermal stability of obtained reclaimed rubber.

Phase-resolving simulation of dense bubble clusters under periodic shear

The paper studies the response of a cluster of bubbles to osmotic pressure, and steady and oscillatory shearing by detailed numerical simulations. In contrast to other investigations, the movement of the interstitial fluid is fully resolved. To that end, an immersed-boundary method is employed, yielding the trajectory of each bubble and the flow and pressure field of the fluid. Additionally, a physically motivated collision model ensures realistic bubble interactions. Furthermore, a suitable numerical configuration is proposed which allows imposing osmotic pressure and shear in a way that integrates well into the simulation without generating artefacts. This method allows for the realistic investigation of the compression of bubbles across the jamming limit, demonstrating the influence of the inertia of the interstitial fluid. Applying oscillatory shearing with varying osmotic pressure, shear stress and frequency, the occurrence of shear bands is demonstrated and the influence on rheometric measurements is discussed.

Dynamic Behavior of Dilute Bentonite Suspensions under Different Chemical Conditions Studied via Magnetic Resonance Imaging Velocimetry

This study investigates dilute aqueous suspensions of bentonite particles using magnetic resonance imaging (MRI) velocimetry. Four different chemical conditions are tested to investigate the influence of pH and type of monovalent electrolyte on the local rheological behavior of bentonite suspensions. The results indicate the shear banding in a dilute suspension of 0.1 vol.% solid due to the formation of a continuous three-dimensional particle network under a certain chemical environment (i.e., pH 4 in 1 × 10−2 M KNO3). This network is responsible for the existence of the yield stress in that dilute suspension. Structural changes induced by modification of suspensions’ chemistry are examined via scanning electron microscopy. A previously established method based on processing the torques acquired via conventional rheometric measurement is also applied as an alternative way to recover local flow information. Within the shear rate range covered by our MRI velocimetry, the results of both methods show good agreement. This study suggests that the existence of a master curve (or global flow curve) for dilute suspensions is dependent on the bentonite particle organization, which is influenced by the suspension chemistry and the previous flow history.

Pressure transmission in yield stress fluids - An experimental analysis

The current work presents an experimental investigation of the pressurization of a yield stress fluid contained in a closed pipeline under isothermal conditions. The tests were performed in a laboratory-scale flow loop placed inside a thermally controlled chamber. Sensors located along the pipeline measured fluid pressure and temperature. Differently from Newtonian fluids, experiments conducted with a viscoplastic fluid showed that the pressure imposed at one end of a closed pipeline was not fully transmitted to the other end, supporting prior mathematical model results. The results also revealed that the final pressure distribution was dependent not only on the fluid yield stress but also on the shear history the fluid underwent during pressurization and on the ratio between the pressure wave inertia and viscous dissipation. A comparison of the fluid yield stress obtained from rheometric measurements with the shear stress at the pipeline wall showed that they were of the same order of magnitude and that the higher the pressure wave inertia-viscous dissipation ratio the higher was the discrepancy between them.

A Study of Concentrated Suspensions in Polyethylene Melts and the Impact on Viscosity and Polymer Processing Operations

AbstractFilled polymer compounds can present processing challenges, including poor dispersive mixing, high screw shaft torque and energy consumption, flow instabilities, and significant increases in melt pressures and temperatures. Previous theoretical development and experimental evaluations of polymer melts filled with particulate solids showed that the viscosity can be described with a model based on percolation theory concepts. This paper describes a batch mixer characterization method developed to measure the effects of filler concentration and operating conditions on the melt viscosity and process response. Experimental results are compared with capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide. The theoretical treatment of the viscosity as a particulate percolating system with power-law behavior was used to analyze and compare rheometer and batch mixer data. The effects of resin molecular weight, filler type and size on viscosity and melt processing were examined and there was good agreement between rheometer and mixer viscosity trends, and percolation model predictions. The laboratory experiments and model estimates provide quantitative information that can be used to develop and troubleshoot extrusion compounding, single screw extrusion and low-shear forming processes.

Functional and practical analytical pressure surges model through herschel bulkley fluids

Substantially large pressure surges are generated while drilling a well due to tripping operations in which a central drillstring is being moved up or down through non-Newtonian fluid. The presence of these subsurface surge pressures must be considered and determined in almost every well drilled. Wells exhibiting high geothermal temperature gradient further complicate the determination of wellbore pressures since the classical viscometer does not characterize the non-Newtonian nature of fluids accurately at elevated temperatures. More importantly, rheological model selection also plays a key role for effectively proposing safe tripping speeds without violating the mud window constraints. Herschel-Bulkley rheological model has gained more reputation among others due to better predictions of wellbore hydraulic pressures as suggested by the American Petroleum Institute.A new practical and dimensional analytical model was developed for Herschel Bulkley (HB) fluid to calculate pressure surges caused by drillstring movement for non-Newtonian fluids under the fully developed flow (steady state) conditions in the laminar flow range in a slot geometry. The proposed analytical method was applied on unweighted fresh water sepiolite mud as a non-Newtonian fluid since the sepiolite muds are among the few water based muds performing adequately at extreme temperatures as the synthetic and oil base muds. Already measured rheological constants of selected fluid system using both HTHP dynamic rheometer and classical viscometer were considered to obtain surge pressures at ambient to extreme temperature ranges. The results are compared with already developed Burkhardt method for Bingham Plastic fluid and Schuh method for Power Law fluid and other proposed numerical and analytical solutions. Substantial differences on the pressure surges between the conventional viscometer and the HTHP rheometer measurements were also presented. The precision of the developed model is shown to be acceptable for most practical applications. Being operationally easy and applicable with a convenient solution code make the proposed model straightforward to be used as a part of drilling software.

TO STUDY THE EFFECT ON THE VISCOELASTIC PROPERTIES OF A MINERAL BASE ENGINE OIL ADDITIVATED BY FUNCTIONALIZED MULTI WALLED CARBON NANOTUBES

The lubricants are most important component of any moving machinery system which helps to reduce the friction and thus overall wear and tear. Objectives: The important viscoelastic properties such as shear rate, shear stress, viscosity, Torque etc. of additivated mineral oil was investigated using a Rheometer and ultrasonic velocity measurements were conducted using nano fluid interferometer. Method: In the current experimental work, Multi Walled Carbon Nanotubes (MWCNT) were coated with stearic acid (carboxylic group) in order to investigate their viscoelastic properties as wear reduction additive for a mineral base engine oil (SAE 20W50). The functional MWCNTs were examined by FTIR technique, Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM). The MWCNTs were then dispersed in a mineral oil by ultrasonication. Findings: The results show that by functionalization of MWCNTs, the viscoelastic properties of the base mineral oil improved as more stable bonds were created on metallic surface due to improved absorption qualities. It was also deduced that due to coating of MWCNTs with carboxylic group stearic acid, the stability of suspension is high and it does not coagulate even after few months. Applications: The improved additivated engine oil finds applications in almost all major automobile uses and to reduce the harmful effect on the environment. Keywords: Carbon Nano-Tubes, Rheology, Viscoelasticity

Shear strength of wet granular materials: Macroscopic cohesion and effective stress : Discrete numerical simulations, confronted to experimental measurements.

Rheometric measurements on assemblies of wet polystyrene beads, in steady uniform quasistatic shear flow, for varying liquid content within the small saturation (pendular) range of isolated liquid bridges, are supplemented with a systematic study by discrete numerical simulations. The numerical results agree quantitatively with the experimental ones provided that the intergranular friction coefficient is set to the value [Formula: see text], identified from the behaviour of the dry material. Shear resistance and solid fraction [Formula: see text] are recorded as functions of the reduced pressure [Formula: see text], which, defined as [Formula: see text], compares stress [Formula: see text], applied in the velocity gradient direction, to the tensile strength [Formula: see text] of the capillary bridges between grains of diameter a, and characterizes cohesion effects. The simplest Mohr-Coulomb relation with [Formula: see text]-independent cohesion c applies as a good approximation for large enough [Formula: see text] (typically [Formula: see text]. Numerical simulations extend to different values of μ and, compared to experiments, to a wider range of [Formula: see text]. The assumption that capillary stresses act similarly to externally applied ones onto the dry granular contact network (effective stresses) leads to very good (although not exact) predictions of the shear strength, throughout the numerically investigated range [Formula: see text] and [Formula: see text]. Thus, the internal friction coefficient [Formula: see text] of the dry material still relates the contact force contribution to stresses, [Formula: see text], while the capillary force contribution to stresses, [Formula: see text], defines a generalized Mohr-Coulomb cohesion c, depending on [Formula: see text] in general. c relates to [Formula: see text] , coordination numbers and capillary force network anisotropy. c increases with liquid content through the pendular regime interval, to a larger extent, the smaller the friction coefficient. The simple approximation ignoring capillary shear stress [Formula: see text] (referred to as the Rumpf formula) leads to correct approximations for the larger saturation range within the pendular regime, but fails to capture the decrease of cohesion for smaller liquid contents.

Application of Low Field Nuclear Magnetic Resonance to evaluate asphalt binder viscosity in recycled mixes

The newly developed method to estimate asphalt viscosity and aging trends using Low Field Nuclear Magnetic Resonance (LF-NMR) was applied to characterize the effect of incorporating recycled materials and recycling agents in asphalt mix samples. The measurements were conducted on asphalt mix samples prepared with different binders: (1) a virgin binder, (2) a recycled binder from Reclaimed Asphalt Pavement (RAP), (3) a blend of virgin and RAP binder (recycled blend) and (4) a rejuvenated blend that consists of the recycled blend with the addition of a recycling agent (tall oil). The LF-NMR measurements were performed at room (25 °C) and magnet (36.4 °C) temperatures. The Relative Hydrogen Index (RHI) obtained from LF-NMR captured the expected binder viscosity trends for the asphalt mix samples prepared with each of the different binders. The viscosity of the binders and blends was estimated from Dynamic Shear Rheometer (DSR) measurements. The relationship between dynamic viscosity and RHI agreed with previous findings. The samples prepared with the rejuvenated blend had lower viscosity and higher RHI than the recycled blend, indicating that the tall oil was effective in lowering its viscosity. Small discrepancies in the trends of the rejuvenated blend as compared to the virgin binder were attributed to their similar detectable hydrogen content, obtained in the rejuvenated blend with the addition of tall oil, but different oxidation state, molecular distribution and steric hindrance. This indicates that the LF-NMR method is more influenced by the chemistry of the asphalt binders rather than their viscosity. The asphalt mix samples with virgin and rejuvenated binders were also subjected to an aging treatment at 70 °C for a month. A significant decrease of the RHI was detected for the samples prepared with rejuvenated binder whereas no significant change was detected for those prepared with virgin binders, which indicates that rejuvenated binders were more susceptible to additional aging that resulted in increased viscosity.