Measurement of Rheology

For the purposes of constant consideration the most significant is the circumstance that all these data on the whole give the information which is equivalent or close to that obtained during measurements of rheological properties under the conditions of shear flow. Therefore a method of investigation here is determined by the taste of the experimenter and measuring technique available. 

The measurement of rheological properties of the PLFNCs in the molten state is crucial in order to gain a fundamental understanding of the nature of the processability and the structure-property relationships for these materials. 

Contraves, Measurement of Rheological Properties, Bulletin T 990 e-8509 CZ, Contraves AG Zurich Zurich, Switzerland, 1985. 

Measurement of Rheology of Distiller s Grain Slurries Using a Helical Impeller Viscometer... 

The general principles of the measurement of rheological properties of milk fat and fat-based products are described in Section 22.4.9. The measurement of other product-specific functional properties, either ingredient properties or end use properties is described in the following. 

Measurements of rheological quantities on the tensile deformation of polymer melts used to be extremely difficult and required the development of special techniques. 

Hamann, D. D. 1987. Methods for measurement of rheological changes during thermally induced gelation of proteins. Food Technol. 41(3) 100, 102-108. 

Additional instrumentation on the unit allows for measurement of temperature and pressure inside the vessel, flow-rate control of the off-speci-fication oil, and measurement of rheological properties of the off-specification and produced oil. 

The flow of liquids or semisolids is described by viscosity, or, more precisely, by shear viscosity (unit Pa sec). The viscosity defines the resistance of the material against flow. Viscosity is not a coefficient, because it is a function of the shear strain rate y [ti = /(y)]. In the classical fluid mechanics, the dynamic viscosity is obtained using a viscometer. (A viscometer is a rheometer, i.e., an instrument for the measurement of rheological properties, limited to... 

The measurement of rheological properties at the surface of a solution or the interface between a solution and, for example, a biological film is called surface or interfacial rheology. In this technique also, experiments are performed either in tension, compression or shear, and phenomena observed in bulk rheology such as flow and viscoelasticity are also observable. An introduction to the techniques available and some key findings are discussed by Warburton. ... 

The complex viscosity as a function of frequency, maximum strain and temperature is generally determined with one rheometer. Standard ASTM 4440-84/90 defines the measurement of rheological parameters of polymer samples using dynamic oscillation. This standard reiterates the importance of determining the linear viscoelastic region prior to performing dynamic frequency sweeps. 

FIGURE 5.9 Illustration of dynamic (oscillatory) measurement of rheological properties. In (a) the applied shear strain (y) is shown as a function of time t oscillation frequency. In (b d) the resulting shear stress a is given for an elastic, a viscous, and a viscoelastic response. 5 is the phase or loss angle. See text. 

Thus far, recent developments in the measurement of rheological properties were discussed. Next, we consider the rheological properties of important PFDs, such as, tomato concentrates and concentrated orange juice. 

N. A. Park, Measurement of Rheological Properties of Non-Newtonian Fluids With the Falling Needle Viscometer, Ph.D. thesis, Mech. Eng. Dept., State Univ. of New York at Stony Brook, 1984. 

Principles of Measurement of Rheological Properties in Lipid-Based Food Systems... 

PRINCIPLES OF MEASUREMENT OF RHEOLOGICAL PROPERTIES IN LIPID-BASED FOOD SYSTEMS... 

The measurement of rheological properties for non-Newtonian, lipid-based food systems, such as dilatant, pseudoplastic, and plastic, as depicted in Figure 4.1, are much more difficult. There are several measurement methods that may involve the ratio of shear stress and rate of shear, and also the relationship of stress to time under constant strain (i.e., relaxation) and the relationship of strain to time under constant stress (i.e., creep). In relaxation measurements, a material, by principle, is subjected to a sudden deformation, which is held constant and in many food systems structure, the stress will decay with time. The point at which the stress has decayed to some percentage of the original value is called the relaxation time. When the strain is removed at time tg, the stress returns to zero (Figure 4.8). In creep experi-... 

Similarly, since much has been written about the importance of the measurement of rheological data in the same range of shear or deformation rates as those likely to be encountered in the envisaged application. Table 1.3 gives typical orders of magnitudes for various processing operations in which non-Newtonian fluid behaviour is likely to be significant. 

Rheological properties Rheology is the study of the deformation and flow of matter under the influence of an applied stress. The measurement of rheological properties is helpful to predict the physical properties of polymer nanocomposites during and after processing. Oberdisse [44] studied the rheological properties of a special nanocomposite material obtained by film formation of mixtures of colloidal silica and nanolatex solutions by means of uniaxial strain experiments. 

Erzin [75] reviewed the influence of material, (compression, molecular weight and intermolecular order), design and processing on the failure of plastic products and discusses failure analysis and testing. This involved measurements of rheological... 

Measurement of Rheological and Viscoelastic Properties of Unreinforced Polymers... 

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