Viscoelastic behaviour of wheat starch pastes

Summary The dynamic mechanical behaviour of starch pastes has been investigated over a frequency range of 0.02 to 5.0 radian sec^–1. The influence of concentration of starch, source of starch and method of paste preparation on rheological properties have been studied. The results suggest that under the conditions examined differences in the dynamic rigidity and viscosity of pastes may be attributed to differences in the number fraction of large granules and the volume fraction of swollen starch particles they contain.With 4 figures and 4 tables     

Small-diameter parallel plate rheometry: a simple technique for measuring rheological properties of glass-forming liquids in shear

The rheological characterization of glass-forming liquids is challenging due to their extreme temperature dependence and high stiffness at low temperatures. This study focuses on the special precautions that need to be taken to accommodate high sample stiffness and torsional instrument compliance in shear rheological experiments. The measurement errors due to the instrument compliance can be avoided by employing small-diameter parallel plate (SDPP) rheometry in combination of numerical instrument compliance corrections. Measurements of that type demonstrate that accurate and reliable rheological data can be obtained by SDPP rheometry despite unusually small diameter-to-gap (d/h) ratios. Specimen preparation for SDPP requires special attention, but then experiments show excellent repeatability. Advantages and some current applications of SDPP rheometry are briefly reviewed. SDPP rheometry is seen as a simple and versatile way to measure rheological properties of glass-forming liquids especially near their glass transition temperature.     

The effect of dissolved polymers on the rheological properties of coating colours

Coating colours used for the coating of paper and board consist mainly of a mineral pigment, which is very often clay, a synthetic binder such as a styrenebutadiene latex, dispersion agents and water retention aids. The latter are often water soluble polymers. These polymers have a very strong influence on the rheological properties of the coating colours, both on the strain rate dependence of the apparent viscosity and on the viscoelasticity. The effects of two different grades of carboxymethylcellulose (CMC) and one grade of hydroxyethylcellulose (HEC), on the rheological properties at room temperature of a clay-based coating colour at pH 8, have been investigated. It is concluded that the high values of the dynamic modulus of the colours are due to interactions between the cellulose derivatives and the solid particles, i.e. mainly the clay particles. For HEC this interaction is associated with adsorption of the polymeric molecules on the clay particles. In the case of CMC, the adsorption is strongly retarded by the presence of the dispersant (a polyacrylate salt). It is suggested that the marked elasticity of the CMC-containing colour in addition to a possible polymer adsorption may be due to charge interactions and/or depletion flocculation. The effect of CMC and HEC on the water-retention properties of the colour is also discussed.     

The use of rheology in the study of the composition effects on the fresh behaviour of hydraulic lime grouts for injection of masonry walls

The injection of grouts inside multi-leaf stone masonries is a technique widely used for structural consolidation. To ensure an adequate flow of the grout inside the masonry, it is crucial to assure good fresh grout properties, such as good rheological behaviour. The scope of this paper is to provide preliminary indications and valuable data about the effects of specific hydraulic lime grout composition on their rheological behaviour with the purpose of a successful injection process. Through the use of rotational rheometer together with the Taguchi method, it was possible to study the influence of water/binder ratio, the type and dosage of superplasticizer and the partial replacement of hydraulic lime by silica fume, upon the grout rheological properties. The study leads to the conclusion that polycarboxylate-based superplasticizers present better performance from a rheological point of view than the naphthalene-based superplasticizer and that the water/binder ratio and superplasticizer dosage are the most determinant factors in the fresh grout rheological behaviour. On the other hand, silica fume dosage turned out to be the factor with the least contribution to improve the grout rheological behaviour compared to the other two factors reported in this study. The results summarised in this paper are part of a larger study and precede the analysis of the performance of those grouts when injected into different porous media that simulate old masonries.     

Influence of mixing conditions on rheological behavior and electrical conductivity of polyamides filled with carbon black

The introduction of carbon black in a polyamide matrix allows one to obtain conductive materials because of the formation of a filler network. Resulting electrical properties depend, among others, on the processing conditions. In a first part, we investigate the influence of mixing conditions (rotor speed, temperature, mixing time) on electrical conductivity. Then, in a second part, we try to characterize the conducting network by rheological measurements and to establish relationships between rheological parameters and electrical properties. For that purpose, we propose to perform successive strain sweep experiments at constant frequency, from 0.5 to 100%, then from 100 to 0.5%, and finally, again, from 0.5 to 100%. Between two successive strain sweeps, we observe a drop in the moduli values that can be attributed to the breakdown of the carbon black network. A clear relationship is established between rheological and electrical properties of the compounds. Moreover, we propose a presentation of the rheological data that permits to rank the samples according to the strength of the carbon black network.     

Rheological behavior of concentrated suspensions as affected by the dynamics of the mixing process

The rheological characterizations of concentrated suspensions are generally carried out assuming “well-mixed” suspensions. However, the variation of the concentration distributions of the ingredients of the formulation, i.e., the “goodness of mixing”, the size and shape distributions of the particle clusters and the rheological behavior of the suspension all depend on the thermo-mechanical history that the suspension is exposed to during the mixing process. Here, various experimental tools are used for the characterization of the degree of mixedness (concentration distributions) of various ingredients along with the characterization of rheological material functions, wall slip behavior and the maximum packing fraction of a graphite/elastomer suspension. The degree of mixedness values of the ingredients of the suspensions processed using batch and continuous processes and under differing operating conditions were characterized quantitatively using wide-angle X-ray diffraction and thermo gravimetric analysis and were elucidated under the light of the electrical properties of the suspension as affected by the mixing process. Upon achieving better homogeneity of the graphite particles and the binder and decreases in the size and breadth of the size distributions of particle clusters (as inferred from electrical measurements and maximum packing fraction values), the elasticity (storage modulus) and the shear viscosity (magnitude of the complex viscosity from small-amplitude oscillatory shear and shear viscosity from steady torsional and capillary rheometry) of the suspension decreased significantly and the wall slip velocity values increased. These findings demonstrate the intimate relationships that exist between the rheological behavior of concentrated suspensions and the thermo-mechanical history that they are exposed to during the processing stage and suggest that the preparation conditions for suspensions should be carefully selected and well documented to achieve reproducible characterization of rheological material functions.     

Influence of surfactant addition on the rheological properties of aqueous Welan matrices

In the present work the effects produced by the presence of two different surfactants (Abil B 8842 and Triton N 101) on the rheological properties of aqueous welan matrices are studied, both in steady and in oscillatory shear conditions. Welan is an acidic microbial polysaccharide having high thermal, pH, and salt stability. At sufficiently low concentrations it forms aqueous weak gel matrices which can be profitably used to regulate the rheological properties of disperse systems and improve their stability. Different systems are examined, having the same polysaccharide concentration (0.25 wt%) and different surfactant concentrations (up to 40 wt%, far beyond the range of practical interest for emulsion preparation). All the systems exhibit marked shear-thinning properties which can be described quite satisfactorily by the Cross equation. The concentration dependence of the zero-shear-rate viscosity as well as the mechanical spectra confirm that, in the concentration range considered, the aqueous welan systems are typically weakly structured fluids. The influence of both surfactants is examined in detail by comparing the behavior of the different classes of systems. Both surfactants reduce the polymer contribution at low shear, whereas an opposite action is exerted at high concentration and shear. These contrasting effects are ascribed to the different structural features of the polymer matrix under low stresses and high shear conditions, respectively. Received: 6 February 2000 Accepted: 1 November 2000     

Creep response of bituminous mixtures—rheological model and microstructural interpretation

The main failure mechanisms of flexible pavements, such as low-temperature cracking, fatigue failure, and rutting are strongly influenced by the viscoelastic properties of asphalt. These viscoelastic properties originate from the thermorheological behavior of bitumen, the binder material of asphalt. In this paper, the bitumen behavior is studied by means of a comprehensive experimental program, allowing the identification of viscoelastic parameters of a power-law type creep model, indicating two time scales (short-term and long-term) within the creep deformation history of bitumen. Moreover, these characteristics of the creep deformation transfer towards bitumen-inclusion mixtures, as illustrated for mastic, consisting of bitumen and filler. For this purpose, the aforementioned power-law creep model is implemented into a micromechanical framework. Finally, the activation of the different creep mechanisms as a function of the loading rate is discussed, using viscoelastic properties obtained from both static and cyclic creep tests.     

Concept evaluations of three novel forwarders for gentler forest operations

In-terrain transport of wood from sensitive areas with soft soil has always been difficult to perform in without extensive rutting and soil distortion. To carry out logging in wintertime, on frozen ground, is increasingly difficult as prolonged, rainy fall seasons and milder winters have decreased the window of opportunity for such operations. This creates strong demands for forest machines that can master soft soils. Exposure to whole body vibrations is a serious problem for operators of forest machines, which is also related to the machine-ground interaction. Both the soil and operator benefit from damped chassis suspension.Vibrations and soil distortion indicate loss of tractive energy. Instead of moving the machine, energy is lost in deformation of the ground and tractive elements, adding to motion resistance and to machine vibrations. Three recent developments of concept machines with improved soil interaction properties, reducing soil impact and improving operator comfort are presented. Two rubber tracked forwarders and one wheeled pendulum arm machine with active damping have been constructed, tested and analyzed.Results from standardized rutting and vibration tests of the concept machines are presented. Notable improvements regarding soil impact and rutting, operator comfort and fuel consumption were found. Some remaining technical challenges are also discussed.     

Flow and blockage of highly concentrated granular suspensions in non-Newtonian fluid

Studying the flow of highly concentrated granular suspensions represents a great challenge since they are characterized by a rather complex rheological behavior. In addition, macroscopic heterogeneities may be induced by the flow during rheological measurements due to the eventual relative motion between the liquid and the granular phases that may take place under certain conditions. Solid–liquid separation may ultimately lead to flow blockage. In the present investigation we consider experimentally the influence of the rheological properties of the suspending fluid on the transition between the flow and blockage of a concentrated suspension in a squeeze set-up geometry. The suspending fluid consists of an aqueous Xanthan solution for which rheological properties can be tuned by changing the polymer concentration. For each polymer concentration, it is shown that there exist flow parameters (squeeze velocity and gap thickness) for which one has a transition between homogeneous flow of the suspension and its blockage. Blockage diagrams, delimiting flowability and blockage zones, are then determined. Physical arguments are given to relate the evolution of the blockage diagrams to the flow parameters and rheological properties of suspending fluid.     

Rheological properties of polyacrylates used as synthetic road binders

Most adhesives and binders, including bitumen for asphalt mixture production, are presently produced from petrochemicals after the refining of crude oil. The fact that crude oil reserves are a finite resource means that in the future, it may become necessary to produce these materials from alternative and probably renewable sources. Suitable resources of this kind may include polysaccharides, plant oils and proteins. This paper deals with the synthesis of polymer binders from monomers that could, in future, be derived from renewable resources. These binders consist of polyethyl acrylate (PEA) of different molecular weight, polymethyl acrylate (PMA) and polybutyl acrylate (PBA), which were synthesised from ethyl acrylate, methyl acrylate and butyl acrylate, respectively, by atom transfer radical polymerisation. The rheological properties of these binders were determined by means of oscillatory testing using a dynamic shear rheometer and combinations of stress/strain, temperature and frequency sweeps. The results indicate that PEA can be produced to have rheological properties similar to that of ‘soft’ 100/150 penetration grade bitumen, PMA with similar rheological properties to that of ‘hard’ 10/20 penetration grade bitumen, while PBA, due to its highly viscous nature and low dynamic moduli, cannot be used on its own as a binder. The synthetic polymers were found to be thermo-rheologically simple, and the shift factors, used to produce the dynamic moduli master curves, were found to fit an Arrhenius function.     

Shear flow rheological properties of vinylon- and glass-fiber reinforced polyethylene melts

Shear viscosity, shear stress and first normal-stress difference have been investigated for glass- and vinylon-fiber filled polyethylene melts over a wide range of shear rate by means of three kinds of instruments. The influence of fiber content and fiber properties on the rheological properties is discussed. The viscosity increases with increasing aspect ratio and fiber content, and the influence of these parameters on the flow properties is evident at low shear rates. The first normalstress difference increases more rapidly with increasing glass fiber content, especially at low shear stresses. The influence of vinylon fibers on the first normal stress-difference vs. shear-stress relationship is different from that of glass fibers.     

A modified rheometer for in-situ radial and tangential SAXS studies on shear-induced alignment

A tooth rheometer designed to investigate the influence of large amplitude oscillatory shear on the macroscopic orientation of complex fluids is described. The rheometer allows in-situ two-directional small-angle scattering measurements, making it possible to observe in particular the orientation process of hierarchically structured block copolymers in dynamics. Experiments performed with a linear poly(vinyl methyl ether) show that, despite a considerable gap/width ratio, the rheometer can be used for adequate rheological measurements. In addition we found an unexpected dependence of the dynamic parameters on the rheometer gap. The small amount of sample required favors the use of this rheometer for measuring the rheological characteristics of new compounds.     

制样方法对初始各向异性砂土三轴剪切力学特性 的影响研究 1)

基于砂土颗粒的毛细效应特性和冻融试验原理,提出一种砂土试样制备方法,能够在0°~90°范围内任意选取沉积方向,且适用于不同颗粒级配的试样。在中围压条件下进行三轴固结排水剪切试验,研究结果表明,毛细效应、冻融相结合的制样方法能够减缓压缩剪切试验的应力-应变关系增长速度,降低试样的抗剪峰值强度,对残余强度的影响相对较弱。在其他应力路径条件下,例如拉伸、减压压缩、等应力压缩等试验中,可以不考虑装样方法的影响。建议的制样方法能够合理应用到砂土初始各向异性的研究工作中。     

基于一维渗流的单轴压缩流变仪研制

传统固结仪在进行固结试验时不能考虑变水头的渗流作用,而一般的渗流仪较难考虑不同压力下试样的流变特性。利用WG-4应力控制式轻便固结仪和QY1-2渗流仪,进行重新设计与改造,获得基于一维渗流理论的单轴压缩流变仪。该仪器可以进行双面排水固结试验、常水头渗透试验、单轴压缩流变试验,特别是可以进行一维渗流条件下试样的流变试验,可以研究在不同渗透压的作用下,土体的流变特性。改装后的设备原理简单,操作简便,通过对比试验,该仪器的测试数据准确、容错率高。     

纳米碳酸钙作为润滑脂添加剂的摩擦学性能及流变行为研究

使用碳化法制备出三种具有不同粒径的纳米碳酸钙颗粒,利用透射电镜(TEM)和X射线衍射仪(XRD)对其形貌及结构组成进行表征.通过UMT-2摩擦学试验机及RS6000流变仪分别考察了纳米颗粒作为润滑脂添加剂的摩擦学性能及流变学行为,并通过X射线多功能电子能谱仪(XPS)对磨斑表面进行分析.结果表明:所制备的三种纳米颗粒均为方解石结构,可以显著提高基础脂的减摩抗磨性能;添加剂浓度及添加剂尺寸均会影响润滑脂最终的摩擦学性能;在最佳添加浓度和尺寸条件下,能够同时获得最佳的抗磨减摩性能;过高的添加剂浓度会影响润滑脂的结构稳定性,进而影响其摩擦学性能;三种纳米添加剂在磨斑表面形成以碳酸钙为主要成分的润滑膜,纳米颗粒物理性质的差异可能导致其摩擦学性能的差异.     

On the modeling of equilibrium twin interfaces in a single-crystalline magnetic shape-memory alloy sample—III: Magneto-mechanical behaviors

This is the concluding part III of a series of papers. The aim of the current paper is to simulate and analyze the procedure of variant reorientation in a magnetic shape-memory alloy (MSMA) sample and to predict the response of the sample subject to various loading conditions. The sample to be considered in this paper has a 3D cuboid shape and is subject to typical magneto-mechanical loading conditions. Variant reorientation in the sample is realized through twin interface movements. To investigate the key features of twin interface movements, the properties of configurational forces on the twin interfaces are analyzed. For both the stress-assisted MFIS tests and the field-assisted quasi-elasticity tests, the magneto-mechanical behavior of the MSMA sample during the whole loading procedure is simulated by using the finite element method. The influence of the initial variant distribution in the sample on its global response is discussed. The obtained numerical results are compared with the experimental results. It can be seen that the model predictions can fit the experimental results both at a qualitative as well as at a quantitative level.     

Rheological aspects of the rejuvenation of aged bitumen

Rheological techniques are used to investigate the rejuvenation of aged bitumen. The thermal transition associated with the collapse of the compact structure constituted by asphaltene is determined by Dynamic Mechanical Thermal Analysis. For aged bitumen, this transition shifts to a higher temperature but when rejuvenating agents are added, the transition returns to its original value. The “rutting factor,” G*/sin δ allows to define the maximum temperature the binder can reach without permanent deformation. The employed rejuvenating agents are suitable because permanent deformation is postponed. Viscosity results reveal that aged bitumen needs a high mixing temperature (>200°C) to behave like a fluid material able to wet, adhere, and envelop aggregates. The addition of rejuvenating agents considerably reduces mixing and compaction temperatures. The mixture of 80% aged bitumen—20% recycled motor oil, obtained exclusively from waste materials is an apt binder that can compete satisfactorily with new 60/70 bitumen.Paper presented at the AERC2005. This paper will be part of a special issue of AERC2005.