Properties rheological

The rheological behavior of xylans has rarely been investigated [4,114,115]. The water-insoluble hemicellulose from the viscose process (containing 85% xylan) was reported to form thixotropic aqueous dispersions of high 

Studies of the structure and molecular size of wheat AX [41] revealed that they are shear-thinning and exhibit two critical concentrations, which correspond to the onset of coil overlapping. The existence of three domains provided the evidence for the formerly suggested rigid, rod-Uke conformation of AX in solution. In a recent study [116], the previously reported conflicting suggestions on the conformation of AX were discussed. 

The viscoelastic properties of carbon nanotube/polymer composites have both practical importance related to composite processing and scientific importance as a probe of the composite dynamics and microstructure. The viscosity for CNT/PU dispersion at mixing is also very important for in-situ formation of polyurethane nanocomposite. Lower viscosity means a better flow ability and more homogenous mixing with isocyanate. Furthermore, low viscosity is very helpful to remove the bubbles before curing, which is a key step for polyurethane preparation. 

As with other mechanical properties, barrier properties are also often significantly improved by clay. Typically, MMT can lead to a decrease in the gas permeability 

Several rheological or related properties can be influenced by antiblocking and slip additives, as follows  

Extmsion and blown fihn production are frequently affected by melt fracture. The melt fracture is caused by flow instabilities of viseoelastic liquids. Fluo-ropolymer based additives are used to eliminate this process instability by coating 

Viscosity is a function of shear stress and seems independent of the amount of the fluoropol5uner additive, but at the lower level of additive (400 ppm) extru-date shows melt fracture above shear rate of 800 s. If more additive is added material is processed successfully at 50% higher shear rate. This is obviously another element of eost and proeess design because higher shear rate also means higher production rate. 

Ceramic slips use additives which may have different effects on viscosity. Polyvinylalcohol, PVA, increases viscosity and acrylic binder reduces viscosity. Also, viscosity may either stay eonstant (acrylic binder) or increase with time (PVA). 

Barrel, head, and gate pressures are frequently reduced by the presence of additives (see example in Figirre 10.38). Reduced gate pressure and lower torque resulted from addition of fluoropol5Tner additive. Melt viscosity usually 

The mechanical and rheological properties are measures of how materials respond when they are deformed. Solids are characterized by mechanical properties such as the Young s modulus, strength and hardness, whereas liquids are characterized by rheological properties such as the viscosity and yield stress. 

When a stress Le. a force per unit area) is applied to a solid, for example it is stretched, sheared, twisted or squashed, it deforms, i.e. changes its length, or shape. For small deformations, the amount of deformation is proportional to the applied stress. The material is said to behave elastically. Beyond a certain deformation (the elastic limit) the material ceases to be elastic, and the material no longer returns to its initial shape when the stress is removed. This is called plastic deformation. If the material is deformed further then it will eventually break. Some materials, such as rubber, are elastic for large deformations, while others, such as plasticine, have a relatively small elastic limit but can then undergo large plastic deformations. Brittle materials, such as china, can only withstand small deformations before they break. 

Liquids have no definite shape, and flow irreversibly when a shear stress is applied. We have already seen the definition of the viscosity of a liquid in Chapter 2 in terms of the shear stress and velocity gradient. 

Since the velocity (v) is the distance travelled (A/) divided by the time (t), equation 2.10 can be rewritten as 

At a typical storage temperature of —18 °C, ice cream displays solidlike properties such as elasticity, plasticity and fracture. A number of 

In this section we begin by reviewing experimental studies of the rheological behavior of unvulcanized elastomers and related materials. We then seek to correlate this behavior in terms of the theory of viscoelasticity. First, the linear theory of viscoelasticity in which there is broad consensus of agreement in the rheological community is discussed. We then describe the nonlinear theory, where the level of consensus is much less. 

The experimental literature largely divides between studies of behavior in small strain and studies in steady shear flow. Much of the emphasis has been to relate such behavior to molecular structure. 

During the 1940s and early 1950s, Leaderman [L4,L5],Tobolsky [A2,A3, Dll, T5], Ferry [F3], and others made extensive studies of the small-strain behavior of elastomers and related polymers. These studies involved creep (deformation under applied stress), stress relaxation following applied stresses, and imposed oscillatory strains. These and other experimental techniques used have been described in special detail in the monograph of Ferry [F3]. These studies showed that all of these deformations could be represented in terms of the superposition principle of Boltzmann [B26] [see Eq.(43)]. 

Tobolsky and his coworkers made extensive efforts to characterize the stress relaxation characteristics of elastomers, notably polyisobutylene. The stress would decay over time to zero at a rate dependent on temperature and molecular weight (Fig. 2). They expressed the relaxation through a series of exponentials or a spectrum of relaxation times. Consider the shear stress decay a t) following an shear imposed strain yo- This may be used to define a shear relaxation modulus G i) through 

FIGURE 2 Stress relaxation from the measurements of Andrews et al. [A2, A3]. 

As with other physico-chemical properties of colloidal microgels the rheological behaviour of dispersions distinctly changes in response to environmental stimuli. At low temperatures the viscoelastic properties of poly(NIPAM) microgels change dramatically with temperature [89, 90]. At low temperatures poly(NIPAM) dispersions display elastic-type behaviour as 

The addition of fillers into polymer matrix can alter the rheological properties of the polymer and its processing performance. The rheological properties are affected by the nature of nanopartides and polymer (e.g., molecular weight and polarity) and nanoparticle-polymer interactions. Meanwhile, the applications of polymer nanocomposites depend on their viscoelastic properties that determine their processibil-ity and mechanical integrity. Although some theoretical work has recently been done, our understanding of the viscoelastic properties of polymer nanocomposites and the influence of nanopartide-polymer interactions is quite immature. 

DPD simulation has been applied to predict the rheological and viscoelastic behaviors of nanopartide-polymer nanocomposites and to examine the effects of particle shape, particle-particle interaction, and partide dispersion states of such behaviors. It was found that partide-particle interaction has a distinct effect on the dynamic shear modulus. Havet and Isayev [39,40] proposed a rheological model to predict the dependence of dynamic properties of highly interactive filler-polymer mixtures on strain and the dependence of shear stress on shear rate. 

MD simulation can gain insight into the viscoelastic behavior of nanopartide-polymer composites. The shear stress relaxation modulus can be calculated using the time autocorrelation function of the stress tensor, while the viscosity is calculated based on the Einstein relations. Compared to conventional composites, the viscoelastic properties are strongly perturbed by the nanopartides and depend upon the nature of nanopartide-polymer interactions. The viscosity and dynamic shear modulus can be dramatically increased for composites with attractive 

The development of polymer nanocomposites needs a comprehensive understanding of the phenomena and an accurate prediction of the material properties and behaviors at different time- and length scales. In the past, this need has significantly stimulated the theoretical and simulation efforts in nanoparticle-polymer nanocomposites. In this connection, many analytical and numerical techniques are employed to predict nanocomposite properties. 

The authors would like to thank Australian Research Council (ARC) for the financial 

Rheological measurements have been conducted to evaluate the dispersion and adhesion qualities between the inorganic particles and polymer matrix and also the processing properties. Chang et studied the effects of micron-sized MH 

Being a disperse system, the foam exhibits a more complex behaviour when subjected to mechanical loading, compared to that of its constituting phases liquid and gas. Of all rheological parameters the latter are characterised by the viscosity alone. The complete description of the foam system requires knowledge of the constants of elasticity (modulus of 

Significant progress in the rheological studies of foams has been achieved in the late 70 s and 80 s [9-16]. The major results of these studies are summarised below. A more detailed analysis of the rheological models, the techniques used and the experimental data obtained can be found in a series of works of Princen et al. [10-13] as well as in several reviews [e.g. 15-18], 

It is convenient to describe Newtonian flow with the aid of a system consisting of two horizontal parallel plates and liquid in between. A tangential force applied to the upper plate shifts it with velocity vg with respect to the lower (immobile) plate. The intermediate liquid layers move with a velocity 

The flow of a Newtonian liquid obeys a law according to which the shear stress r = F/A is related to the rate gradient (rate of shear) as follows 

In t vs. dv/dl co-ordinates this equation yields a straight line, beginning at the coordinates origin. For a foam this reological dependence is given by a curve, the slope of which as well as its ordinate axis-intercept, are determined by the foam expansion ratio. However, several other types of empirical relation have been proposed instead of Eq. (8.10) [19-22], The simplest and most widely used is the equation of Shvedov-Bingham 

Like any disperse system, foams produce non-Newtonian systems and to characterise its rheological properties one need to obtain information on the elasticity modulus (modulus of compressibility and expansion), the shear modulus, yield stress and effective viscosity, elastic recovery, etc. 

It is difficult to study the rheological properties of a foam since on deformation its properties change. The most convenient geometry to measure foam rheology is a parallel plate. The rheological properties could be characterised by a variable viscosity (4), 

Deryaguin [33] obtained the following expression for the shear modulus, 2 2 /2 4y 

Princen [35] used a two-dimensional hexagonal package model to derive an expression for the shear modulus and yield stress of a foam, taking into account the foam expansion ratio and the contact angles. 

For a dry foam (p- l), the yield stress can be calculated from the expression, 

Newton s law states that for a liquid under shear, the shear stress T is proportional to the shear rate. In this sense, most of the unpigmented vehicles used in the paint and printing ink industries are considered ideal or Newtonian liquids. The ratio of the shear stress t to the shear rate D is thus a constant t), dependent only on temperature and pressure. This is not true for specialized gel varnishes and thixotropic systems, which are designed to have special rheological properties. 

A Casson fluid is Theologically identified by two parameters yield value and plastic viscosity. The plastic viscosity relates to the asymmetry of the flow particles and the yield value is connected with the forces of attraction between particles. The 

The ultimate viscosity T) of a pigmented medium is practically independent of the particle size, but increases appreciably with rising pigment volume concentration and higher vehicle viscosity [114], 

Thixotropy is one of the reversible time-dependent effects that constitute nonideal behavior (Fig. 54). 

An increasing pigment concentration is associated with more or less pronounced thixotropy (Figs. 53 and 54). Thixotropic systems have a gel structure. 

However, while the Cox-Merz rule is valid for general unfilled and low concentration filled systems, it was discovered that the rule fails to hold for concentrated suspensions. It is important at this point to recognize that MIM or PIM feedstock is essentially a concentrated suspension at elevated temperature. A modified Cox-Merz rule was developed for cmicentrated suspensions by Doraiswamy et a [20]. The modified rule stated that the complex viscosity versus shear rate amplitude plot is equal to the corresponding viscosity versus shear rate plot. That is 

Recent literature has shown that the modified Cox-Merz rule could fit e rimental data very well [20-22], Isayev and Fan [22] of University of Akron investigated both steady and oscillatory shear flow behavior of silicon-polypropylene ceramic compoimd. They reported that steady shear measurement with either parallel plate or capillary rheometers posed a 

The effects of shear rate on the rheological behavior of feedstocks were extensively studied. Dependence of viscosity on shear rate can be expressed by the power law equation. 

Yield stress has been observed in MIM feedstock suspensions at low shear rates and low shear stress conditions [1,11,13], A yield stress of a fluid can be defined as the limiting shear stress that has to be exceeded to initiate a shear flow. A fluid that exhibits such a yield stress is termed viscoplastic [29]. When an applied stress is less than a particular stress (yield stress), the 

Yield stress fluids can be found in a diversity of fields, such as biomedical, food processing and engineering materials. Important examples include concentrated suspensions, pastes, emulsions, gels, paints, blood and other body fluids. 

When a shear stress is applied to a suspension or liquid exhibiting laminar flow, a velocity gradient (the rate of shear) is established. When the rate of shear varies linearly with the applied shear stress, the system is termed Newtonian and the proportionality constant is termed the viscosity. Newtonian flow is usually observed in dilute 

The rheological properties of a suspension depend upon factors such as the size, shape and concentration of the particles, the stability of the suspension and the viscosity of the medium. Flow properties can be modified by altering the surface charge 

Rheological studies involving Fe oxides appear to be sparse. Most are carried out on acicular crystals, usually maghemite. Details of the method of synthesis or properties of the particles are often lacking. 

Cerpa et al. (1999) found a relationship between the yield stress and the volume fraction of a laterite suspension consisting of serpentine (a day mineral) and goethite. 

The adsorption of ions on iron oxides regulates the mobility of species in various parts of the ecosystem (biota, soils, rivers, lakes, oceans) and thereby their transport betv een these parts. Examples are the uptake of plant nutrients from soil and the movement of pesticides and other pollutants from soils into aquatic systems. In such environments various ions often compete with each other for adsorption sites. Adsorption is the essential precursor of metal substitution (see Chap. 3), dissolution reactions (see Chap. 12) and many interconversions (see Chap. 14). It also has a role in the synthesis of iron oxides and in crystal growth. In industry, adsorption on iron oxides is of relevance to flotation processes, water pollution control and waste and anticorrosion treatments. 

The values of ACPo and ACPl are the differences in the heat capacity between the glassy and rubbery state for the uncured resin and the fully cured network, respectively. However, the parameter A can also be used as a fitting parameter. 

Mixing activated cure materials such as polyurethanes will instantly start releasing exothermic heat after the mixture of its two components has occurred. The Castro-Macosko curing model, a second order reaction kinetic, accurately fits this behavior and is written as [44], 

In the above equations, the exponent of the (1 — c)n term determines, which order reaction is being used to best fit the reaction kinetics. How these properties that describe the conversion or reaction are used, will be covered in more detail in Chapter 6 of this book. 

Mild acid modification of oat starch had a great affect on the viscoelastic behavior of pastes during cooling. Acid-modified oat starch underwent one transition in viscoelastic behavior below 40°C, G increased and 6 decreased, due to gelation of amylose. The transition below 90°C typical for native oat starch was not observed after acid modification. This finding is in agreement with that of Paton,43 who found that treatment with acid almost eliminated the exceptionally high viscosity measured at 80°C for native oat starch. 

Schrickel DJ. In Webster FH, ed. Oats, Chemistry and Technology. St. Paul, MN American Association of Cereal Chemists 1986 1. 

Anderson JW, Seisel AE. In Furda I, Brine CJ, eds. New Developments in Dietary Fiber Physiological, Physicochemical and Analytical Aspects. New York, NY Plenum Press 1990 17. 

Anderson JW, Deakins DA, Bridges SR. In Kritchevsky D, Bonfield C, Anderson JW, eds. Dietary Fiber Chemistry, Physiology and Health Effects. New York, NY Plenum Press 1990 339. 

AW propagation velocity is sensitive to changes in the density of any medium in contact vrith the substrate surface. Inspection of the mass-loading term for AW devices (Chapter 3 Equatirm 5.1) reveals an implicit dependence of wave velocity on the density of a coating layer. Note that a density change need not occur in a surface-immobilized film in order to be detected changes in the ambient medium produce an effect as well. TSM [61], SAW [11], and FPW devices have been utilized to monitor the pressure (via the density) of gases. 

For liquid-phase sensing, both density and viscosity, as well as the nature of the acoustic mode, play a role in AW perturbations. For TSM and SH-APM devices, in-plane motion of the substrate surface entrains a thin layer of liquid through viscous coupling. Entraiiunent of a liquid layer by the sensor surface constitutes a mass load proportional to the product of thickness and density of the coupled liquid layer, giving rise to a velocity change. 

The log-log plots of apparent shear stress versus apparent shear rate for STR5L/ EPDM and STR5L/BEPDM blends with various blend compositions are shown in Figs. 15.12 and 15.13, respectively (71). Flow curves of all the blends show reasonably straight hnes, whose intercept K and slope n correspond to the power law equation (the Ostwald-de Waele equation) (72). Table 15.4 shows the power law index and the consistency of flow of STR5L/EPDM and STR5L/BEPDM blends. The values of n n 1) indicate the pseudoplastic nature of STR5L, EPDM, BEPDM, and their blends. 

According to the Cates s theory, the terminal time for stress relaxation (Tr) and the zero-shear viscosity (T o) follows the seating relation [24] 

We have also fitted the shear-rate dependence of the viscosity to the following equation [27, 28] 

Juan Carlos Garcia and Antonio Francisco Marcilla 

Departamento de Ingenieria Quimica de la Universidad de Alicante, Spain 

However, the temperature of maximum torque does not correspond with the temperature of complete fusion, as suggested by MacKiimey since after the peak, incompletely fused PVC, is still present. 

Plasticizer Time, min Temperature of fiisiorr, °C Torque, Nm 5pvC last 

The dispersion levels of the clay platelets helps in retaining the viscosity both at lower and higher temperatures. The anisotropy and small size prevent free rotation of the clay platelets and increases the viscosity. In addition to this, in in-situ clay-polymer hybrid, chemical bonding between the s-caprolactum and oigano-ions of clay platelets is the reason for the higher viscosity than the melt-blended system, where only physical interaction occurs. 

The effect of the chain length of the surfactant compound can be seen from Fig. 11.17. For systems with the same concentrations the modulus increases with increasing chain length from Cio to Ci6 and decreases for Cig. This means that the modulus is not only determined by the electrostatic repulsion between the bilayers but also depends on the thickness of the bilayers. 

An interesting effect is shown in Fig. 11.20 where the shear viscosity / as a function of the shear rate y and the magnitude of the complex viscosity / as a function of the angular 

Denoting the displacement vector for the translations by u and for the rotations by a, and assuming that all displacements are small, the symmetrical part of the strain tensor can be written as  

A strain described by leads to a symmetric stress tensor (7 in materials with elastic response. The force per unit area/on a surface of the surrounding body has the components  

Here is a unit vector pointing outward normal to the considered surface element. As usual in tensor calculus, we imderstand smn over equal suffixes when they occur in the same term and if not indicated differently. The force per unit volume due to the stress is  

To account for the torques that the particles exert on each other, we define the elements of the torque tensor related to the torsions analogous to Accordingly, the torque per unit area is  

27 coefficients. This means altogether 171 possible parameters, which is impossible to handle both theoretically and experimentally. Fortunately, 

6 Arborescent Folystyrene-graft-Po y(tert-Buty Methacrylate) 

Branching functionalities / ranging from 9 500 and molecular weights ranging from 8.8 X 10 -6.3 X 10 with narrow MWD (Mw/Mn 1.05-1.10) were thus obtained. 

They adopted a semi-empirical equation with two fitting parameters that were determined from experiment on highly concentrated oil-in-water emulsions of varying radius, interfacial tension and volume fraction. The equation they obtained is as follows  

Rheological measurements performed on highly concentrated W/0 emulsions (gel emulsions) showed that the equation proposed by Princen also holds for these systems. Measurements of the viscoelastic properties showed that these materials have a viscoelastic response that can be fitted to a Maxwell liquid element. The elastic and viscous terms of this model vary as a function of frequency as  

These parameters were also shown to depend on the system variables such as composition and temperature. The elastic modulus at high frequency is equivalent in these systems to the shear modulus and depends on the interfacial tension, droplet radius and volume fraction in the way predicted by eqn. (11.1) within 

Gel Emulsions—Relationship between Phase Behaviour and Formation 

Both data sets show this maximum, although the experimental agreement is not very good. The appearance of these maxima is due to the compensation of the effect of temperature on the interfacial tension and on the droplet size. As temperature inereases the interfacial tension in nonionic surfactant systems above the HLB temperature increases this implies an increase in the elastic modulus. At the same time, an increase in temperature produces an increase in droplet size (not only related to coalescence but to the interfacial tension as well ). An increase of droplet size produces a decrease of the elastic modulus. At low temperatures the interfacial tension dominates, at an intermediate point both factors compensate and at high temperatures the droplet size finally dominates. The dependence of the 

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Additives Modifying the Rheological Properties of Lubricating Oils... 

It is very important, from one hand, to accept a hypothesis about the material fracture properties before physical model building because general view of TF is going to change depending on mechanical model (brittle, elasto-plastic, visco-elasto-plastic, ete.) of the material. From the other hand, it is necessary to keep in mind that the material response to loads or actions is different depending on the accepted mechanical model because rheological properties of the material determine type of response in time. The most remarkable difference can be observed between brittle materials and materials with explicit plastic properties. 

Doi, M. and Edwards, S.F., 1978. Dynamics of concentrated polymer systems 1. Brownian motion in equilibrium state, 2. Molecular motion under flow, 3. Constitutive equation and 4. Rheological properties. J. Cheni. Soc., Faraday Trans. 2 74, 1789, 1802, 1818-18.32. 

Fats contribute to the rheological properties in flowable and pastry foods. By combining with starches to form a clathrate, a product different from the native starch is formed, eg, shortening in baked goods. The highly developed shortness of pies baked in eadier times resulted from the use of high levels of lard. The use of less fat in pie cmsts is evident, ie, the cmsts are harder and readily become soggy. 

Rheology. The rheology of foam is striking it simultaneously shares the hallmark rheological properties of soHds, Hquids, and gases. Like an ordinary soHd, foams have a finite shear modulus and respond elastically to a small shear stress. However, if the appHed stress is increased beyond the yield stress, the foam flows like a viscous Hquid. In addition, because they contain a large volume fraction of gas, foams are quite compressible, like gases. Thus foams defy classification as soHd, Hquid, or vapor, and their mechanical response to external forces can be very complex. 

Solutions of rhamsan have high viscosity at low shear rates and low gum concentrations (90). The rheological properties and suspension capabiUty combined with excellent salt compatibihty, make it useful for several industrial apphcations including agricultural fertilizer suspensions, pigment suspensions, cleaners, and paints and coatings. 

Preformed Two-Piece Metal Containers. Ink vehicles for letterset printing of two-piece aluminum or steel containers are mainly based on special polyester vehicles used in conjunction with melamine cross-linkers. Short cycle ovens which dry inks in 1—5 seconds are now used and operate at temperatures as high as 350 °C. The rheology of these inks must be adjusted to the unique geometry of the press. Desired rheological properties are achieved by the use of additives as weU as extender pigments. 

The process of flushing typically consists of the foUowing sequence phase transfer separation of aqueous phase vacuum dehydration of water trapped in the dispersed phase dispersion of the pigment in the oil phase by continued appHcation of shear thinning the heavy mass by addition of one or more vehicles to reduce the viscosity of dispersion and standardization of the finished dispersion to adjust the color and rheological properties to match the quaHty to the previously estabHshed standard. 

Rheology is the science of the deformation and flow of matter. It is concerned with the response of materials to appHed stress. That response may be irreversible viscous flow, reversible elastic deformation, or a combination of the two. Control of rheology is essential for the manufacture and handling of numerous materials and products, eg, foods, cosmetics, mbber, plastics, paints, inks, and drilling muds. Before control can be achieved, there must be an understanding of rheology and an ability to measure rheological properties. 

Tests on raw or compounded but unvulcanized materials are chiefly concerned with rheological properties, that is, the response to the forces imposed during the operations of mixing, extmsion, calendering, and curing. 

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