Newtonian shear viscosity

The viscosity of some polymers at constant temperature is essentially Newtonian over a wide shear rate range. At low enough shear rates all polymers approach a Newtonian response that is, the shear stress is essentially proportional to the shear rate, and the linear slope is the viscosity. Generally, the deviation of the viscosity response to a pseudoplastic is a function of molecular weight, molecular weight distribution, polymer structure, and temperature. A model was developed by Adams and Campbell [18] that predicts the non-Newtonian shear viscosity behavior for linear polymers using four parameters. The Adams-Campbell model is as follows ... 

A simulation was carried out with the melting model using the simulation conditions described earlier for the PE resin with a Newtonian shear viscosity of 220 Pa-s. For this simulation, the pressure at the end of the solids-conveying section... 

NON-NEWTONIAN SHEAR VISCOSITY AND FIRST NORMAL STRESS COEFFICIENT OF POLYMER MELTS... 

FIG. 15.13 Non-Newtonian shear viscosity r/(q) at 170 °C vs. shear rate, q, for the polystyrene mentioned in Fig. 15.12, measured in a cone and plate rheometer (O) and in a capillary rheometer ( and ) and the dynamic and complex viscosities, rj (w) (dotted line), rj (w) (dashed line) and i (< ) (full line), respectively, as functions of angular frequency, as calculated from Fig. 15.12. From Gortemaker (1976) and Gortemaker et al. (1976). Courtesy Springer Verlag. 

Van Krevelen DW and Hoftyzer PJ (1976) Newtonian shear viscosity of polymer melts. Angew Makromol Chem 52 101-9. 

The non-Newtonian shear viscosity, tj, versus shear rate is given in Figure 3.5. It is noted that at low shear rates 17 is a constant, 170- As shear rate increases, the viscosity decreases—a manifestation of pseudoplastic behavior. The viscosities generally decrease with MFR. At high shear rates, in the range of fiber spinning, the viscosities differ by a factor of only 1.5. 

Cox and Merz [C20] have made the remarkable experimental observation that the non-Newtonian shear viscosity function of flexible chain polymers has the same form as the complex viscosity-frequency function, i.e.. 

Formulas for linear viscoelastic models can be apphed to tensile deformation as well as shear deformation by replacing the shear stress x with tensile stress o, shear strain y with tensile strain e, shear modulus G with Young s tensile modulus E, and newtonian shear viscosity T with Trouton s tensile viscosity iig [11—13]. 

Dependence of Non-Newtonian Shear Viscosity on Shear Rate... 

In addition to non-Newtonian shear viscosity, which has been mentioned in Sections C2 and C5. there are a wide variety of nonlinear phenomena observed in various types of deformation, especially shear and simple (uniaxial) extension for deformations with large strains and large strain rates. Some of these have been mentioned in Chapters I and 3. Nonlinear behavior in shear has been studied mostly... 

K. C. Seavey, Y. a. Liu, N. P. Khare, T. Bremner, C.-C. Chen, Quantifying relationships among the molecular weight distribution, non Newtonian shear viscosity, and melt index for linear polymers , Ind. End. Chem. Res., 2003, 42, 5354. 

In these equations, pi denotes the density of the liquid at 20 °C, d the diameter of the nozzle exit, tj o and Mi are the upper Newtonian shear viscosity and the velocity of the liquid at the nozzle tip, respectively. For spray droplets, the characteristic length is usually defined by the diameter of the nozzle tip. Since the main focus of this part of the study was the dispersirm of secondary emulsion droplets, the secondary emulsion droplet diameter JC50.3 of the treated emulsion was preferably applied as the characteristic length. 

The models developed here are visualized in tension, with tensile stress cr, tensile strain s, and Young s modulus E. However, the same theory holds true for pure shear (viscometric) deformation, where a shear stress t results in a shear strain y with proportionality constant G (Hooke s modulus), rj represents the Newtonian (shear) viscosity, while the elongational (Trouton) viscosity is given by rjg. 

The initial compliance 1(0) can be very small. The recoverable compliance jR(t) rises to a limiting value as the internal elastic processes reach their limiting strains. Finally, the material flows and the strain increases linearly in time with a slope determined by the true Newtonian shear viscosity. 

Typical shear viscosity-shear rate curves are shown in Fig. 1.5. In studying shapes of non-Newtonian shear viscosity-shear rate plots, Vinogradov and Malkin [41 ] found that the dependence of r//Tf(i upon T/g y was independent of temperature. They concluded that the behavior of all polymer melts was the same and could be fitted with the relationship of form ... 

Figure 3.9 Non-Newtonian shear viscosity of poiymer soiutions...

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