Rheology pseudo plastic

Rheology pseudo-plastic highly pseudo-plasiic F low high-Shear viscosity 1- good runnability -1- reduces blade oressure... 

The non-aqueous HIPEs showed similar properties to their water-containing counterparts. Examination by optical microscopy revealed a polyhedral, poly-disperse microstructure. Rheological experiments indicated typical shear rate vs. shear stress behaviour for a pseudo-plastic material, with a yield stress in evidence. The yield value was seen to increase sharply with increasing dispersed phase volume fraction, above about 96%. Finally, addition of water to the continuous phase was studied. This caused a decrease in the rate of decay of the emulsion yield stress over a period of time, and an increase in stability. The added water increased the strength of the interfacial film, providing a more efficient barrier to coalescence. 

The effect of pseudo-plasticity was reportedly known for different plastisols, in particular, for plastisols II described in Sect. 3. The rheological behaviour of these systems with an accuracy sufficient for the purposes of engineering is given by the Bingham-Shvedov law within the extended range of shear rates (10-2 < y < 102) ... 

The melt flow under isothermal conditions, when it is described by the rheological equation for the Newtonian or power law liquid, has been studied in detail63 66). The flow of the non-Newtonian liquid in the channels of non-round cross section for the liquid obeying the Sutterby equation have also been studied 67). In particular, the flow in the channels of rectangular and trigonal cross section was studied. In the analysis of the non-isothermal flow, attention should be paid to the analysis 68) of pseudo-plastic Bingham media. 

Solyom and Ekwall (20) have studied rheology of the various pure liquid crystalline phases in the sodium caprylate-decanol-water system at 20 °C, for which a detailed phase diagram is available. Their experiments using a cone-and-plate viscometer show that, in general, apparent viscosity decreases with increasing shear rate (pseudo-plastic behavior). Values of apparent viscosity were a few poise for the lamellar phase (platelike micelles alternating with thin water layers), 10-20 poise for the reverse hexagonal phase (parallel cylindrical micelles with polar... 

There are two general types of constitutive equations for fluids Newtonian and non-Newtonian. For Newtonian fluids, the relation between the stress tensor, t, and the rate of deformation tensor or the shear stress is linear. For non-Newtonian fluids the relation between the stress tensor and the rate of deformation tensor is nonlinear. The various Newtonian and non-Newtonian rheologies of fluids are shown in Figure 12.2. There are four types of behavior (1) Newtonian, (2) pseudo-plastic, (3) Bingham plastic, and (4) dilatent. The reasons for these different rheological behaviors will also be discussed in subsequent sections of this chapter. But first it is necessary to relate the stress tensor to the rate of deformation tensor. 

At h h polymer concentrations, polymer molecules entangle, producing pseudo-plastic rheological behavior. This occurs at a polymer concentration, cf = comparable to that in the polymer... 

Cross, M.M. Rheology of non-Newtonian fluids a new flow equation for pseudo-plastic systems. J. Colloid Sci. 1965, 20, 417 37. 

Simple classifications of fluids can be made on the basis of their rheological profiles. Figure 3.78 shows the (a) shear stress and (b) viscosity profiles for various systems. From Figure 3.78 one may define the following systems. Newtonian systems have a constant viscosity with respect to shear rate. Dilatant (or shear-thickening) systems have a viscosity that increases with respect to shear rate. Pseudo-plastic (or shear-thinning) systems have a viscosity that decreases with respect to shear rate. Yield-stress materials are materials that have an initial structure that requires a finite stress before deformation can occur. The stress that initiates deformation is defined as the yield stress. 

Rheological Nature Gum Arabica is a polyelectrolyte soluble in water over a wide range of concentration below 40% concentration pseudo-plastic characteristics are observed, denoted by a decrease in viscosity. VN th increasing temperature the relative viscosity and density of gum Arabica solution decreases. 

This studies have shown that the rheological parameters are affected by the type of measuring device, composition of the paste and rheological history of the sample. The pastes can be attributed to the Newtonian or non-Newtonian types of liquid between the later the plastic (Bingham), pseudo-plastic or exhibiting the dilatancy phenomena can be differentiated. Moreover, the pastes reveal basically the thixotropy or anti-thixotropy properties. 

If the shear rates are constants, the non-Newtonian fluids can also be classified according to their viscosity dependence on time. This classification has been widely applied to describe the rheological characteristics of coatings. For the development of deformation, the time evolution corresponds to the effect of the increase of shear rate. Three typical cases occur with the time evolution the thixotropic fluids exhibit the decrease of viscosity, corresponding to pseudo-plastic fluids the rheopectic fluids exhibit the increase of viscosity, corresponding to dilatant fluids while the viscoelastic fluids exhibit partial recovery of the deformation of pseudo-plastic fluids after the removal of the stress. Since polymers can perform a large scale of elastic deformation, this character appears extremely significant. 

The given presentation of the mechanism of the interaction of polymer molecules with turbulent flow admits a peculiar theoretical examination. The presence of polymer addition besides the increase of longitudinal viscosity is resulted in the appearance of such rheological solution properties as elastic plasticity, pseudo-plasticity, anisotropy. In [3] the influence of different rheological fluid characteristics on the wall turbulence is theoretically analyzed within the limits of monoharmonic approximation, which affords to take into account turbulent blows-out. Different variants of rheological behaviour were considered. For all that we succeded to show, that the decrease of turbulent friction arose only in mediums, possessing... 

Flow properties See melt-flow index, viscosity, pseudo-plastic fluid, and rheology. 

Viscosity enhancing substances not only increase the viscosity but also introduce rheological qualities such as (pseudo) plastic, dUatant and thixotropic behaviour (see Sect. 18.2.1). 

It is now important to calculate the stress exerted by the particles. This stress is equal to aApgfZ. For polystyrene latex particles with radius 1.55 pm and density 1.05 g cm , this stress is equal to 1.6 x 10 Pa. Such stress is lower than the critical stress for most EH EC solutions. In this case, one would expect a correlation between the settling velocity and the zero shear viscosity. This is illustrated in Chapter 7, whereby v/a is plotted versus 7(0). A linear relationship between log( /a ) and log 7(0) is obtained, with a slope of —1, over three decades of viscosity. This indicated that the settling rate is proportional to [7(0)] . Thus, the settling rate of isolated spheres in non-Newtonian (pseudo-plastic) polymer solutions is determined by the zero shear viscosity in which the particles are suspended. As discussed in Chapter 7, on rheological measurements, determination of the zero shear viscosity is not straightforward and requires the use of constant stress rheometers. 

As mentioned above, food systems are complex multiphase products that may contain dispersed components such as sohd particles, hquid droplets or gas bubbles. The continuous phase may also contain colloidally dispersed macromolecules such as polysaccharides, protein and lipids. These systems are non-Newtonian, showing complex rheology, usually plastic or pseudo-plastic (shear thinning). Complex structural units are produced as a result of the interaction between the particles of the disperse phase as well as by interaction with polymers that are added to control the properties of the system, such as its creaming or sedimentation as well as the flow characteristics. The control of rheology is important not only during processing but also for control of texture and sensory perception. 

The basic principles of rheology and the various experimental methods that can be applied to investigate these complex systems of food colloids have been discussed in detail in Chapter 7. Only a brief summary is given here. Two main types of measurements are required (1) Steady-state measurements of the shear stress versus shear rate relationship, to distinguish between the various responses Newtonian, plastic, pseudo-plastic and dilatant. Particular attention should be given to time effects during flow (thixotropy and negative thixotropy). (2) Viscoelastic behaviour, stress relaxation, constant stress (creep) and oscillatory measurements. 

Flow curves - Melt rheological properties of PES were evaluated on a capillary instrument attached to a Shimadzu Universal Materials Testing Machine model AG-IOTA. Viscosity curves measured at 315, 330 and 350°C and for shear rates ranging from 10 to 10000 1/s are presented in Figure 1. A typical pseudo-plastic behavior can be seen. That is, the melt viscosities of PES decrease with the increase of apparent shear rates. 

The rheology (thixotropy, i.e. pseudo-plastic, or dilatant flow) must be considered and adjusted or the coating will not apply well (see later for fuller details). 

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