Pseudoplastic shear thinning

This equation is based on the assumption that pseudoplastic (shear-thinning) behaviour is associated with the formation and rupture of structural linkages. It is based on an experimental study of a wide range of fluids-including aqueous suspensions of flocculated inorganic particles, aqueous polymer solutions and non-aqueous suspensions and solutions-over a wide range of shear rates (y) ( 10 to 104 s 1). 

Use anionic polymers such as polyacrylic acids cross-linked with allyl ethers of pentaerythritol or sucrose as thickeners, if a gel structure and pseudoplastic (shear-thinning) properties are desirable. Consider adding colloidal alumina to further increase the viscosity at pH 13 [ 15]. 

Before the viscosity can be calculated from capillary data, as mentioned above, the apparent shear rate, 7 , must be corrected for the effect of the pseudoplastic nature of the polymer on the velocity profile. The calculation can be made only after a model has been adopted that relates shear stress and shear rate for this concept of a pseudoplastic shear-thinning material. The model choice is a philosophical question [11] after rheologlsts tried numerous models, there are in general two simple models that have withstood substantial testing when the predictions are compared with experimental data [1]. The first Is ... 

The apparent viscosity of PVC pastes varies with the shear rate applied, so that they rarely, if ever, exhibit truly Newtonian behaviour. The rheological properties of plastisols can range from pseudoplastic ( shear thinning ) to dilatent ( shear thickening ), as illustrated in Figure 107. 

An understanding of the rheological behaviour is necessary as PVC pastes are classified as non-Newtonian liquids and can be dilatent (shear thickening), pseudoplastic (shear thinning) or thixotropic (viscosity reduces with time under constant shear). Each process requires specific rheological characteristics and this is achieved by formulation of appropriate PVC grades and knowledge of the influence of shear rate and time under constant shear. 

Dilatant Fluids. Dilatant fluids or shear-thickening fluids are less commonly encountered than pseudoplastic (shear-thinning) fluids. Rheological dilatancy refers to an increase in the apparent viscosity with increasing shear rate (3). In many cases, viscometric data for a shear-thickening fluid can be fit by using the power law model with n > 1. Examples of fluids that are shear-thickening are concentrated solids suspensions. 

Deviations of liquids from Newtonian behavior are frequently observed for pharmaceutical and biomedical systems. In these, the relationship between stress and the rate of strain is nonlinear, examples of which include pseudoplastic (shear thinning), dilatant (shear thickening), plastic, and Bingham and Ostwald systems (1,17). Such systems are commonly referred to as non-Newtonian systems. 

The hydrolysis of starches by amylases Is most conveniently considered In terms of sugar production (for saccharification) or viscosity reduction (for liquefaction). Starch pastes are characteristically pseudoplastic (shear thinning), and thus satisfy, over an Intermediate range of shear rates, a power law relationship between shear stress, T, and shear rate, y, of the form (2.4) ... 

Pseudoplastic (shear thinning) As shear rate increases viscosity decreases Paint, polymer solutions In paint, a suspension of pigment particles in a liquid, irregular particles can align to match the induced flow, lowering the viscosity... 

Pseudoplastic Shear thinning. This term is used to describe a slip that becomes more fluid when shear stress is applied. The shear thinning behavior is totally reversible in a pseudoplastic slip. Mustard and catsup are commonly seen pseudoplastic fluids. 

In practice, dilatant and rheopectic behavior are often undesirable because at high shear rates the suspension becomes too stiff to flow smoothly. Plastic behavior is desirable for many ceramic forming methods because the suspension will flow under high stress but will retain its shape when the stress is removed after forming. Pseudoplastic (shear thinning) behavior is often an acceptable compromise. 

Solution Rheology. Solutions of polyacrylamides tend to behave as pseudoplastic fluids in viscometric flows. Dilute solutions are Newtonian (viscosity is independent of shear rate) at low shear rates and transition to pseudoplastic, shear thinning behavior above a critical value of the shear rate. This critical shear rate decreases with the polymer molecular weight, polymer concentration, and the thermodynamic quality of the solvent. A second Newtonian plateau at high shear rates is not readily seen, probably because of mechanical degradation of the chains... 

Figures 18.34 and 18.35 showed the apparent shear viscosity at various apparent shear rates for MNR-STR/STR 5L and MNR-ADS/ADS blends, respectively. The pseudoplastic (shear-thinning) behaviour in the flow of all types of blends was observed with the power law index, n, lower than 1. That is, the apparent shear viscosity decreased with an increase in the apparent shear rate. From the linear relation on a log-log scale, one can get the slope (n) and intercept (K), which are shown in the plots of the n and K values against the level of MNR in the blend compositions as shown in Figures 18.36 and 18.37, respectively.

Guar gum shear thinning behaviour and the non-Newtonian pseudoplastic Carboxymethylation shear thinning behaviour and the non-Newtonian pseudoplastic shear thinning behaviour increase with increase in concentration [138]... 

Shear Thinning Flow. Dispersions showing a decrease in viscosity with shear rate (or shear stress) are described as shear thinning or pseudoplastic. Shear thinning behavior is generally produced by the reversible breakdown of suspension structures or alignment of anisotropic particles due to shear. 

Pseudoplastic (shear thinning) adhesives can be prepared by adding polyaciylates such as sodium or ammonium poly aery late. Starch, cel-... 

Unfortunately, many fluids do not obey Newton s hypothesis. Both dilatant (shearthickening) and pseudoplastic (shear-thinning) fluids have been observed (Figure 14.2). On log-log coordinates, dilatant flow curves have a slope greater than 1 and pseudoplastics have a slope less than 1. Dilatant behavior is somewhat uncommon but has been reported for certain slurries and imphes an increased resistance to flow with intensified shearing. Polymer melts and solutions are invariably pseudoplastic, that is, their resistance to flow decreases with the intensity of shearing. 

Rheology deals with deformation and flow and examines the relationship between stress, strain and viscosity. Most theological measurements measure quantities related to simple shear such as shear viscosity and normal stress differences. Material melt flows can be split into three categories, each behaving differently under the influence of shear as shown in Figure 10.9 Dilatent (shear thickening), Newtonian and Non-Newtonian pseudoplastic (shear thinning) behaviour. 

Pseudoplastic shear thinning rheology approaching Newtonian... 

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