Effect of Shear Rate on Viscosity

Figure 9. Effect of shear rate on viscosity of 0.75 mol% RAM as a function of polymer concentration.

The effect of shear rate on viscosity has been discussed in some detail in the previous sections. However, there are some other variables that also affect the viscosity. Two important variables that influence the viscosity are temperature and pressure. The effect of these variables is generally not as strong as the effect of shear rate however, in many cases, the effect of temperature and/or pressure on viscosity cannot be neglected. 

FIGURE 6.1 Effect of shear rate on viscosity at different TLCP/PEN compositions (a) and the effect of TLCP/PEN compositions on the melt flow index (b). (Adapted from Kim Yun Seong et al. Composites Part A., 40, no. 5, 607-612, 2009.)... 

The effect of shear rate on viscosity in this equation is very strong, and demonstrates the typical situation with flocculated systems where severe shear thickening is seen, giving what looks like a yield stress. 

Fig. 4.22. The effect of shear rate on viscosity of aqueous tragacanth solutions, a Flake form tragacanth, 1% b tragacanth, ribbon form, 0.5% (according to Whistler, 1973)...

Figure 8.16 Effect of shear rate on the viscosity of gum solutions grouped according to their rheological behaviour.

The effects of shear rate on the viscosity of thermosets are usually measured on uncatalysed resins or resins that have undergone minimal curing. This is because the effects of shear rate will be most prevalent in the early stages of the process, during transfer or injection of the resin. 

The most common measuring systems used for the effects of shear rate on the chemo-viscosity of thermosets have been the parallel-plate rheometer and the capillary rheometer however, the choice of rheometer is dependent on the type of system to be studied. The advantages and limitations of these systems are presented in Table 4.6. 

Wessel and Ball " and Kanai et al. studied in detail the effects of shear rate on the fractal structure of flocculated emulsion drops. They showed that the size of the floes usually decreases with the increase of the shear stress often the floes are split to single particles at high shear rates. As a result, the viscosity decreases rapidly with the increase of the shear rate. 

Ogorzalek (II) has studied in detail the effect of shear rate on the viscosity of organosols. His data for low shear (Brookfield) and high shear (Extrusion Rheometer) viscosity characteristics using alcohols as diluents are shown in Figures 36 and 37. 

Figure 18.4 Effect of shear rate on melt viscosity at 275° C of PA6, PE, and PA6/PE blend compatibi-lized by PE-g-MAH containing 0.27 wt% of grafted MAH. Ciphers on curves stand for compatibilizer concentration in wt%, PE stands for LDPE/LHDPE (88 12) blend LHDPE is copolymer of ethylene and octene. Reproduced from Reference (66) with permission from John Wiley Sons. Inc.

Figure 4. Effect of shear rate on apparent viscosity of 10%(w/v) solution of A)poly(4VMP/pSS), B)poly(MPTMA/AMPS), and C)poly(METMA/MES) in various salt solutions at 2S C.

Figure 3.12 The effect of shear rates on polymer chain rotation. Hydrodynamic work is converted into heat, resulting in an increased solution viscosity.

In addition to viscosity measurements, the capillary rheometer (Gottfert Rheograph 2002) was used to investigate the effect of shear rate on the morphology of the blends prepared earlier in the corotating twin-screw extruder (A see Tables 2 and 3) with an output of 5.4kg/h. In these capillary extrusion experiments, the shear rate was varied from 150 to 8000see by adjusting the speed of the piston. The strand was allowed to fall freely into the water bath without extension. 

Figure 6.2 Effect of shear rate on PLA-melt viscosity (adapted from Fang and Hanna, 1999, with permission of Elsevier).

The most common way of studying the motion of polymer molecules in such media is to use relaxation techniques to measure the effect of shear rate on, or the frequency dependence of, the real and imaginary parts of the modulus, the comphance or the viscosity as discussed in Chapter 8. In so doing, it is usually... 

The effects of shear rate on the rheological behavior of feedstocks were extensively studied. Dependence of viscosity on shear rate can be expressed by the power law equation. 

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