Pseudoplastic, definition

Several researchers reported viscoelastic behavior of yeast suspensions. Labuza et al. [9] reported shear-thinning behavior of baker s yeast (S. cerevisiae) in the range of 1 to 100 reciprocal seconds at yeast concentrations above 10.5% (w/w). The power law model was successfully applied. More recently, Mancini and Moresi [10] also measured the rheological properties of baker s yeast using different rheometers in the concentration range of 25 to 200 g dm. While the Haake rotational viscometer confirmed Labuza s results on the pseudoplastic character of yeast suspension, the dynamic stress rheometer revealed definitive Newtonian behavior. This discrepancy was attributed to the lower sensitivity of Haake viscometer in the range of viscosity tested (1.5 to 12 mPa s). Speers et al. [11] used a controlled shear-rate rheometer with a cone-and-plate system to measure viscosity of... 

Definition High m.w. hetero polysaccharide gum produced by a pure-culture fermentation of a carbohydrate with Xanthomonas campestris-, contains D-glucose, D-mannose, and D-glucuronic acid and is prepared as the sodium, potassium, or calcium sait Properties Wh. to cream-colored powd., si. organic odor, tasteless sol. in hot or cold water producing vise, highly-pseudoplastic sol ns. insol. in oils, most org. soivs. vise, 600 cps min. unaffected by high or low pH... 

There are three types of melt behavior in a simple shear flow dilatant (D) (shear thickening) Newtonian (N), and pseudoplastic (P) (shear thinning). Similarly, in an extensional flow, the liquids may be stress hardening (SH), Troutonian (T), or stress softening (SS). By definition, the response considered here is taken at sufficiently... 

It is customary to account for the non-Newtonian fluid behavior by introducing the so called effective viscosity to define various dimensionless groups. Unlike its constant value for Newtonian liquids, the effective viscosity of non-Newtonian pseudoplastic type fluids depends upon the operating conditions (e.g., gas and liquid velocities) as well as on the geometrical details of the system. Indeed, the lack of a rationed definition of the apparent viscosity or characteristic shear rate appears to be the main impediment in extending the well established predictive correlations for Newtonian media to non-Newtonian media. When we develop correlations for design parameters in bubble columns with non-Newtonian media in an analogous manner to the case of Newtonian media, Newtonian viscosity p is simply replaced by an apparent viscosity for non-Newtonian media. 

The pumps, metering, mixing and application systems must be adapted to the viscosity of both the components. The viscosities of the two components should be similar in order to get a good mixing effect a very liquid product could not be mixed efficiently with a very thick product. Rheology, of course, must be also adapted the products may be pseudoplastic, thixotropic but never dilatant (for these definitions, refer to Chapter 2 in Volume 1 Technical Characteristics of Adhesives and Sealants ). 

For a Newtonian system the viscosity at levels A and B is the same (by definition). For the pseudoplastic system the viscosity at A is greater than that at B. In a plastic system with a yield value between A and B, no settling would occur. Samyn s own discussion of these cases is given in the legend to the figure. 

The emphasis in this chapter is on the viscous behavior of polymeric fluids and in particular their pseudoplastic behavior. The chapter is arranged in the following manner. First, in Section 2.1 we review the definition of a Newtonian fluid, and then we present empiricisms for describing the viscosity of polymeric fluids. In Section 2.2... 

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