Rheometer Data Research Articles

Curve-fitting equation for prediction of the start-up stress overshoot of an oil-based drilling fluid

Drilling fluids usually gel at rest in order to avoid cuttings to precipitate over the drill bit when circulation is interrupted. At flow start-ups, pumping pressures higher than the steady-state circulation pressure are usually required to surpass the gel strength. The gel-liquid transition may have significant importance, especially in ultra-deep waters where high pressures and low temperatures take place. In the current work, controlled shear rate rheometric tests were conducted to investigate the yielding of an oil based drilling fluid. An algebraic equation, that accounts for both shear rate and shear history, is proposed to predict the gel breaking. This equation requires less fitting parameters than the current structural kinetic models available in literature, and is quite useful to represent the pressure peaks that take place during drilling fluid flow start-ups. The equation fit to rheometric data and is able to predict satisfactorily the start-up shear stress of a gelled drilling fluid at different shear rates.

Probing Rubber Cross-Linking Generation of Industrial Polymer Networks at Nanometer Scale.

We present improved analyses of rheometric torque measurements as well as (1)H double-quantum (DQ) nuclear magnetic resonance (NMR) buildup data on polymer networks of industrial compounds. This latter DQ NMR analysis allows finding the distribution of an orientation order parameter (Dres) resulting from the noncomplete averaging of proton dipole-dipole couplings within the cross-linked polymer chains. We investigate the influence of the formulation (filler and vulcanization systems) as well as the process (curing temperature) ending to the final polymer network. We show that DQ NMR follows the generation of the polymer network during the vulcanization process from a heterogeneous network to a very homogeneous one. The time variations of microscopic Dres and macroscopic rheometric torques present power-law behaviors above a threshold time scale with characteristic exponents of the percolation theory. We observe also a very good linear correlation between the kinetics of Dres and rheometric data routinely performed in industry. All these observations confirm the description of the polymer network generation as a critical phenomenon. On the basis of all these results, we believe that DQ NMR could become a valuable tool for investigating in situ the cross-linking of industrial polymer networks at the nanometer scale.

Analysis of variance in capillary rheometry

The effect of deformation history (hysteresis) on transient capillary rheometric data was studied compared to conventional assumptions regarding steady state data. The factors studied were: the position instrumentation, the pressure instrumentation, entrance and exit effects, polymer melt compressibility, pressure dependence of the viscosity, and polymer melt viscous heating. Statistical analysis of variance (ANOVA) was performed to statistically determine the sources of variance to specific degrees of confidence. The polymer melt compressibility, pressure dependence, and viscous heating were found to be statistically significant contributors of the observed variation at the 95% confidence level; the capillary length and instrumentation were not found to be significant. The results indicate that the transient behavior can vary the modeling of the apparent viscosity in a significant manner such that the model fidelity and model coefficients may vary substantially. Hence, polymer melt compressibility, pressure dependence, and viscous heating should be considered during rheological model fitting to increase model fidelity and predictive accuracy in end-use. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

High-density polyethylene/halloysite nanocomposites: morphology and rheological behaviour under extensional and shear flow

The paper describes the preparation of High Density Polyethylene [HDPE]/Halloysite Nanotube [HNT] nanocomposites by melt compounding HDPE with varying amounts of HNTs (ranging from 1 to 10 % w/w) in the absence and presence of MA-g-HDPE as compatibiliser using co-rotating twin screw extruder. The effect of HNT loading and compatibiliser amount on morphology and rheological properties was investigated. Melt strength and drawability were determined using Rheotens whereas extensional viscosity was calculated from (i) Wagner’s master curve (using Rheotens data) and (ii) modified Cogswell method (using convergent flow analysis from capillary rheometer data). In HDPE/HNT composites, melt extensional properties (melt strength, drawability and extensional viscosity) increased slightly with increase in HNT concentration up to 5 % w/w followed by a decrease as HNT concentration was increased to 10 % w/w. On the other hand all these properties enhanced significantly in the presence of compatibiliser i.e. in HDPE/MA-g-HDPE/HNTs nanocomposites. Rheological studies form capillary rheometer showed marginal increase in the high shear viscosity at 10 % w/w filler loading. Both Complex viscosity and storage modulus in oscillatory rheometry were highest for nanocomposites prepared using 10 % w/w HNT and reduced slightly after incorporation of compatibiliser.

A novel online rheometer for elongational viscosity measurement of polymer melts

This paper focuses on the measurement of elongational viscosity of polymer melts and filled compounds using a novel online rheometer. We developed a device with two slit sections and a hyperbolic contraction part in between, which allows for constant monitoring of both shear and elongational viscosity during an extrusion process. Due to the favorable design of the hyperbolic contraction, pressure transducers can be incorporated directly into the flow channels, which prevents material accumulation in pressure holes. The results of a pipe-grade polypropylene random copolymer melt are in good accordance with Sentmanat Extensional Rheometer (SER) measurements, in contrast to other methods such as Cogswell analysis of High Pressure Capillary Rheometer (HPCR) data or measurement on a wedge-shaped slit die, which fail to predict the true non-Newtonian behavior of the melt. In addition, we present the results of a polypropylene homopolymer intended for thermoformed packaging applications, a glass fiber and a talc compound, which could all be successfully characterized using our rheometer.

Biomechanical Analysis of Infectious Biofilms.

The removal of infectious biofilms from tissues or implanted devices and their transmission through fluid transport systems depends in part of the mechanical properties of their polymeric matrix. Linking the various physical and chemical microscopic interactions to macroscopic deformation and failure modes promises to unveil design principles for novel therapeutic strategies targeting biofilm eradication, and provide a predictive capability to accelerate the development of devices, water lines, etc, that minimise microbial dispersal. Here, our current understanding of biofilm mechanics is appraised from the perspective of biophysics , with an emphasis on constitutive modelling that has been highly successful in soft matter. Fitting rheometric data to viscoelastic models has quantified linear and nonlinear stress relaxation mechanisms, how they vary between species and environments, and how candidate chemical treatments alter the mechanical response. The rich interplay between growth, mechanics and hydrodynamics is just becoming amenable to computational modelling and promises to provide unprecedented characterisation of infectious biofilms in their native state.

Laminar flow of Non‐Newtonian thickened tailings slurry through an open channel

The flow of non‐Newtonian materials through open channels has been little‐studied compared to research on circular pipes. This paper presents a new Reynolds number to predict the flow of non‐Newtonian thickened mining tailings slurries in open channels. Our aim is to model the frictional forces caused by a material's rheology in the laminar regime. The flow behaviour predictions by this and previous models are discussed and validated against previously published experimental data. It is shown that the newly‐defined Reynolds number achieves an appropriate evaluation of the friction at the boundary and average velocities, when compared with the experimental data for Kaolin and Bentonite suspensions. The new model requires rheometer data to determine the fluid index (). It is preferred, as with tube viscometry, to set up a lab‐scale flume from which can be determined graphically or by numerical differentiation. Alternatively the fluid index can be obtained from conventional rotational viscometry results.

Effect of drying method on rheological, thermal, and structural properties of chestnut flour doughs

The objective of this work was to characterize the functional, thermal and rheological properties of chestnut flour doughs produced through freeze-drying (FD) and tray-drying (TD) process. Drying method did not influence the physicochemical properties (e.g. bulk density, water holding capacity and sediment volume fraction) of chestnut flour however affected both particle mass distribution and color values (a and b) significantly. Thermal analysis of chestnut doughs showed two distinct peaks attributed by starch gelatinization and melting of starch–lipid complex, respectively. Although there were only minor differences in the total starch contents between two chestnut flour, they displayed significant variability in pasting properties and oscillatory rheology during heating. The amylograms of the chestnut dispersions showed higher maximum viscosity and heat stability for the FD sample, as well as a higher tendency to the molecular re-association during cooling than for the TD flour. Pasting properties of chestnut doughs were well described by rheometric measurement and data obtained through both measurements are comparable. The chestnut doughs exhibited predominating solid-like property (G′ > G″). The mechanical rigidity (G′) of doughs significantly influenced by the concentration and the increase in G′ with concentration was well described by a power-type relationship. The chestnut granules exhibited a range of shapes, varying from round, oval, rectangular to irregular. Average particle diameter of the tray-dried sample was larger than the freeze-dried sample. This study provides in-depth knowledge on structural/rheological properties of chestnut flour by two drying processes, which would be helpful for selection of ingredients and their application in food industries.

Effect of cholesterol and triglycerides levels on the rheological behavior of human blood

Important public health problems worldwide such as obesity, diabetes, hyperlipidemia and coronary diseases are quite common. These problems arise from numerous factors, such as hyper-caloric diets, sedentary habits and other epigenetic factors. With respect to Mexico, the population reference values of total cholesterol in plasma are around 200 mg/dL. However, a large proportion has higher levels than this reference value. In this work, we analyze the rheological properties of human blood obtained from 20 donors, as a function of cholesterol and triglyceride levels, upon a protocol previously approved by the health authorities. Samples with high and low cholesterol and triglyceride levels were selected and analyzed by simple-continuous and linear-oscillatory shear flow. Rheometric properties were measured and related to the structure and composition of human blood. In addition, rheometric data were modeled by using several constitutive equations: Bautista-Manero-Puig (BMP) and the multimodal Maxwell equations to predict the flow behavior of human blood. Finally, a comparison was made among various models, namely, the BMP, Carreau and Quemada equations for simple shear rate flow. An important relationship was found between cholesterol, triglycerides and the structure of human blood. Results show that blood with high cholesterol levels (400 mg/dL) has flow properties fully different (higher viscosity and a more pseudo-plastic behavior) than blood with lower levels of cholesterol (tendency to Newtonian behavior or viscosity plateau at low shear rates).

Investigations of Nitrile Rubber Composites Containing Imidazolium Ionic Liquids

SummaryThis work aimed to investigate the impact of hydrophobic imidazolium ionic liquids with alkyl chains of varying length attached to the cation imidazolium ring on the rheometric data, the mechanical, morphological, thermal and conductive properties of acrylonitrile‐butadiene rubber (NBR) composites. The presence of ionic liquids not only increased the conductivity (AC) of the composites but also influenced their curing behaviour and mechanical properties. A maximum conductivity of 8.9 · 10−8 S · cm−1 was achieved at room temperature in the NBR sample containing 15 phr (parts per hundred rubber) of 1‐hexyl‐3‐methylimidazolium bis(trifluoromethane‐ sulfone)imide (HMIM TFSI). Moreover, the presence of HMIM TFSI at 15 phr loading in the NBR composite contributed most significantly to the downward shift in the glass transition temperature (Tg) from ‐30 to −33 °C, indicating a plasticizing effect

On cohesive sediment erosion: A first experimental study of the local processes using transparent model materials

An annular flume combined with a microscopic system is used to explore local erosion mechanisms of transparent cohesive beds (yield stress fluids) under shear-induced flowing liquid. The observations at a microscopic scale for erosion flume experiments are the originality of this work. Our first results reveal that the deformation and erosion dynamics of bed material mainly depends on its miscible state with the flume fluid, its structural organization being associated with mechanical properties and the measurement section. Shear localization within the bed is also observed. Moreover, the erosion rate and the local bed shear stress can vary with time even for an imposed constant global hydrodynamic flow as they result from the coupling between the fluid flow and cohesive bed conditions at the bottom. We also try to link the local resistance to erosion to the local cohesive strength estimated from rheometric microscopic data for the same sample conditions with homogeneous properties.

The impact of imidazolium ionic liquids on the properties of nitrile rubber composites

The purpose of this work was to investigate the influence of hydrophilic imidazolium ionic liquids on the curing kinetics, mechanical, morphological, thermal and conductive properties of acrylonitrile–butadiene rubber (NBR) composites. NBR/SiO2/IL composites were prepared by the conventional melt mixing method. It was found that 1-ethyl-3-methylimidazolium thiocyanate (EMImSCN) and 1-methyl-3-octylimidazolium chloride (OMImCl) improved the ionic conductivity of NBR composites. Moreover, both ionic liquids strongly influenced the rheometric data and mechanical properties (static and dynamic). NBR – based composites displayed elastomeric properties and high tensile strength up to 19MPa when 10phr EMImSCN was added. The presence of 30phr EMImSCN in the composite resulted in an increase in its conductivity from 10−11S/cm (NBR/SiO2) up to approximately 10−5S/cm (NBR/SiO2/EMImSCN30) at room temperature. Thermal analysis showed that the Tg of NBR/SiO2/IL systems, decreased as a function of increasing ionic liquid content due to a plasticizing effect, particularly for samples containing OMImCl.

Rheological modelling of dispersions of casein micelles considered as microgel particles

Rheological behavior of dispersions of casein micelles (CM) was predicted through a viscosity model in which CM were considered as microgel particles. A simple structure for CM composed of a spherical core with a brush of κ-casein was considered. An explicit relationship between viscosity and shear stress allows obtaining key parameters such as the packing fractions corresponding to the shear stress limits and the critical shear stress closely related to the total interaction potential between two CM. The analysis of the model parameters fitted from experimental viscosity curves indicates that CM at concentrated regime behave as soft spheres. In addition, the model provides the pair interaction energy between CM directly from rheometric data. The values obtained agree with a DLVO-like theory previously proposed for CM. Indeed, using independent experimental data and parameters, it was possible to cross check both models. The results obtained are very promising for studying CM dispersions as colloidal systems and the stability of dairy products under different physicochemical environments.

High frequency linear rheology of complex fluids measured from their surface thermal fluctuations

We characterize the linear viscoelastic properties of complex fluids using a new technique, based on the measurement of surface fluctuations: surface fluctuation specular reflection (SFSR) spectroscopy. The thermally excited waves propagating on a free surface are measured through the deflection of a laser beam specularly reflected from that surface. Elastic and loss moduli of the complex fluids are inferred from the measured power spectrum density of thermal noise, with the implicit use of Kramers–Kronig relations. The technique, besides being noninvasive, provides rheological data in a large frequency range and at vanishing strains. It is therefore especially well suited for the rheological characterization of complex fluids. We present measurements of the viscoelastic modulus of supramolecular polymer solutions in a frequency range extending up to six decades. We compare the SFSR measurements with rheometric data at low and high frequencies, and show that they are in good agreement. Using supramolecular polymer solutions of different natures, exhibiting or not surface viscoelasticity, we furthermore show that SFSR provides a characterization of the bulk properties of the fluids. In addition, we discuss the accuracy of the measurements.

Mechanical Stability and Fibrinolytic Resistance of Clots Containing Fibrin, DNA, and Histones

Neutrophil extracellular traps are networks of DNA and associated proteins produced by nucleosome release from activated neutrophils in response to infection stimuli and have recently been identified as key mediators between innate immunity, inflammation, and hemostasis. The interaction of DNA and histones with a number of hemostatic factors has been shown to promote clotting and is associated with increased thrombosis, but little is known about the effects of DNA and histones on the regulation of fibrin stability and fibrinolysis. Here we demonstrate that the addition of histone-DNA complexes to fibrin results in thicker fibers (increase in median diameter from 84 to 123 nm according to scanning electron microscopy data) accompanied by improved stability and rigidity (the critical shear stress causing loss of fibrin viscosity increases from 150 to 376 Pa whereas the storage modulus of the gel increases from 62 to 82 pascals according to oscillation rheometric data). The effects of DNA and histones alone are subtle and suggest that histones affect clot structure whereas DNA changes the way clots are lysed. The combination of histones + DNA significantly prolongs clot lysis. Isothermal titration and confocal microscopy studies suggest that histones and DNA bind large fibrin degradation products with 191 and 136 nM dissociation constants, respectively, interactions that inhibit clot lysis. Heparin, which is known to interfere with the formation of neutrophil extracellular traps, appears to prolong lysis time at a concentration favoring ternary histone-DNA-heparin complex formation, and DNase effectively promotes clot lysis in combination with tissue plasminogen activator.

Inducible nitric oxide releasing poly-(ethylene glycol)-fibrinogen adhesive hydrogels for tissue regeneration

ABSTRACTNitric oxide (NO) release can promote healthy tissue regeneration. A PEG-fibrinogen adhesive hydrogel that would allow for inducible NO release was created with mechanical properties that could be tailored to specific applications and tissue types. PEG (4-arm)-fibrinogen hydrogels of varying ratios were derivatized with S-nitroso-N-acetyl-D, L-penicillamine (SNAP)-thiolactone to create an active NO donor material. Controlled release from gels was established using light as the activating source, although temperature, pH, and external mechanical loading are also means to induce active NO release. Gels with varying ratios of fibrinogen to PEG were made, derivatized, and tested. Gels below a ratio of 1.5:1 (fibrinogen:PEG) did not gel, while at ratio of 1.5:1 gelation occurs and NO release can be induced. Interestingly, the release from 1.5:1 gels was significantly lower compared to 2:1 and 3:1 gel formulations. Rheometric data show that lower ratio gels are more elastic than viscous. Derivatized gels exhibited linear elastic moduli, behaving more like other more synthetic hydrogels. Swelling data indicates that as the ratio of fibrinogen to PEG increases the swelling ratio decreases, likely due to the hydrophobic nature of the NO donor. Cells remain viable on both derivatized and non-derivatized gels.

Behavior of Selected Warm Mix Asphalt Additive Modified Binders and Prediction of Dynamic Modulus of the Mixes

Abstract This study evaluated the viscoelastic properties of a performance grade binder modified with different dosages of a selected wax-based warm mix asphalt (WMA) additive (WMA1). The effects of reduced rolling thin film oven (RTFO) aging on the stiffness of the WMA1-modified binder were also evaluated. The viscoelastic properties of the modified binders were then used to estimate the dynamic modulus (E*) values of the WMA mixes through time temperature superposition principles. Furthermore, the effects of a selected liquid anti-stripping agent (ASA), ASA1, on the properties of the WMA1-modified binder were investigated. It was observed that the linear viscoelastic limits of WMA1-modified binders decreased with an increasing dosage of WMA1. Reduced RTFO aging was found to have significant effects on the stiffness of the WMA1-modified binder. The Hirsch model was found to provide better approximations of the E* values than the Witczak model. The Witczak model, based on dynamic shear rheometer data, was found to significantly underestimate the E* values. Although ASA1 did not reduce the beneficial effects of WMA1, it was found to increase the E* values of the WMA mix. The findings of this study are expected to offer transportation professionals a better understanding of the evaluation of WMA binders and mixes.

COMPREHENSIVE NUMERICAL MODEL FOR THE INTERPRETATION OF CROSS-LINKING WITH PEROXIDES AND SULFUR: CHEMICAL MECHANISMS AND OPTIMAL VULCANIZATION OF REAL ITEMS

ABSTRACT This work presents a comprehensive numerical model to optimize mechanical properties of thick rubber vulcanized items, comprising medium and high voltage electric cables and three-dimensional devices. Several vulcanization systems are considered, including peroxides and accelerated sulfur. For peroxides, both a genetic algorithm (GA) and an alternating tangent (AT) approach are adopted to determine the optimal final mechanical properties (tensile strength) of rubber items. The use of a mixture of peroxides is also considered, demonstrating that balanced mixtures may help in reducing the curing time and/or in increasing the optimal tensile strength in both core and skin of thick devices. For sulfur vulcanization, a mathematical kinetic model is presented to predict the cross-linking density of vulcanized rubber. The model is conceived to fit experimental rheometer data, and it is suitable to have an estimate of cross-linking degree at fixed temperature. The model requires a parametric calibration by means of only three kinetic constants, successively implemented in Finite Element (FE) software, specifically developed to perform thermal analyses on two-dimensional geometries. As an example, an extruded cylindrical thick EPDM item is considered and meshed through four-noded isoparametric plane elements. Several FE simulations are repeated changing both exposition time, tc, and external curing temperature, Tc, to evaluate for each (tc, Tc) couple the corresponding mechanical properties of the item at the end of the thermal treatment.

Preparation, characterization and properties of whey-soy proteins co-precipitates

The preparation and gelling characteristics of soybean protein-whey protein co-precipitates were investigated. Mixtures of defatted soy flour and whey powder (Mixed Powder, MP) and mixtures of soy protein extract and whey protein extract (Mixed Extract, ME) were used. The protein co-precipitates were prepared by combination of NaOH extraction and isoelectric-cooling precipitation (ICP) and isoelectric-heating–cooling precipitation (IHCP). The effect of extraction and co-precipitation on co-precipitate yield was investigated. Co-precipitate was obtained using the following conditions of extraction; extraction temperature, 40 °C; temperature of precipitation 98 °C, and pH of precipitation was 4.5. The yield of co-precipitates was affected by chelating agents and pH of precipitation and temperature of precipitation. SDS–PAGE and Native-PAGE slab gel electrophoresis studies indicated that polymerized products consist of proteins coming whey protein and soybean protein, in addition to a new band. Gels were prepared by heating 8%, 12% and 16% dispersions (pH 8.0) of protein co-precipitates at 95 °C for 90 min, and were characterized by measurement of gel strength, and water holding capacity (WHC). Sixteen percent gels from protein co-precipitate MPICP exhibited higher WHC and gel strength compared to WPICP, SPICP, and protein co-precipitates MEICP, MPIHCP and MEIHCP. Oscillation rheometric data indicated that protein concentration directly influenced gel rigidity and, thus, concentration at 16% resulted stronger gel strength and WHC.

Rheology and processing of suspensions with fiber, disk and magnetic particles

This paper introduces recent development and progress in rheology and processing of suspension materials. In particular, three topics with different suspensions will be discussed, which are relevant in polymer- and powder-based manufacturing industries for various applications. The paper begins with a fundamental study of rheological modeling for short fiber suspension in a viscoelastic liquid. Irreversible thermodynamics based approach is presented to describe the polymer viscoelastic deformation with the fiber anisotropy effect taken into account. Several distinguishing features of the model are presented. Then we turn our attention to more industry-oriented subject of pigment disk orientation in injection molding of aesthetic plastic parts. The major difference between fiber and disk orientation kinematics is briefly discussed using Jeffery model. Experimental and numerical results for the disk orientation and the surface color of the molded part are presented. Finally, we introduce our recent efforts regarding the rheology of magnetic particle suspension, which is an essential part for a development of precision magnetic powder injection molding process. Some rheometer data for stainless steel powder suspensions are presented.