Apparent shear viscosity

Linear novolac resins prepared by reacting para-alkylphenols with paraformaldehyde are of interest for adhesive tackifiers. As expected for step-growth polymerization, the molecular weights and viscosities of such oligomers prepared in one exemplary study increased as the ratio of formaldehyde to para-nonylphenol was increased from 0.32 to 1.00.21 As is usually the case, however, these reactions were not carried out to full conversion, and the measured Mn of an oligomer prepared with an equimolar phenol-to-formaldehyde ratio was 1400 g/mol. Plots of apparent shear viscosity versus shear rate of these p-nonylphenol novolac resins showed non-Newtonian rheological behavior. 

Similar observations were noted when FKM/o-MMT clay nanocomposites were prepared by melt blending and the as-prepared nanocomposites showed both intercalated as well as exfoliated structure [103]. The apparent shear viscosity of the FKM/o-MMT nanocomposites was lower than that of the pristine polymer at all shear rates and temperatures. The nanocomposites exhibited reduced equilibrium die swell with a smooth extrudate appearance. A comparison of the flow properties of the nanocomposites with the conventional composites revealed that the nanocomposites exhibited improved processability. 

Serum layer thickness (%) Apparent shear viscosity. Pa s... 

Figure 7.9 Effect of pectin (DE = 76%) on (a) creaming of protein-stabilized emulsions (11 vol% oil, 0.6 wt% protein, 0.28 wt% pectin, I = 0.01 M) containing (A) asi-casein (pH = 7), (A) p-casein (pH = 7), and ( ) o i-casein (pH = 5.5) and (b) steady-state shear viscometry of casein-stabilized emulsions (40 vol% oil, 2 vt% protein). Apparent shear viscosity at 22 °C is plotted against stress pH = 7.0, / = 0.01 M, (A) -casein, (A) p-casein, ( ) ocsi -casein + 0.5 wt% pectin, ( ) p-casein + 0.5 wt% pectin, ( ) p-casein + 1.0 wt% pectin, (O) as[-casein + 1.0 wt% pectin pH = 5.5,1 = 0.01 M, (x) ocsi -casein, (O) as[-casein + 0.5 wt% pectin, ( ) oc -casein + 1.0 wt% pectin. Reproduced from Semenova (2007) with permission.

Chapter HI relates to measurement of flow properties of foods that are primarily fluid in nature, unithi.i surveys the nature of viscosity and its relationship to foods. An overview of the various flow behaviors found in different fluid foods is presented. The concept of non-Newtonian foods is developed, along with methods for measurement of the complete flow curve. The quantitative or fundamental measurement of apparent shear viscosity of fluid foods with rotational viscometers or rheometers is described, unithi.2 describes two protocols for the measurement of non-Newtonian fluids. The first is for time-independent fluids, and the second is for time-dependent fluids. Both protocols use rotational rheometers, unit hi.3 describes a protocol for simple Newtonian fluids, which include aqueous solutions or oils. As rotational rheometers are new and expensive, many evaluations of fluid foods have been made with empirical methods. Such methods yield data that are not fundamental but are useful in comparing variations in consistency or texture of a food product, unit hi.4 describes a popular empirical method, the Bostwick Consistometer, which has been used to measure the consistency of tomato paste. It is a well-known method in the food industry and has also been used to evaluate other fruit pastes and juices as well. 

Figure 17.2 Dependence of the apparent shear viscosity on the shear rate for HDPE (melt index 0.5 g/10 min).

A theoretical explanation for the increase of the viscosity t) could be found in the so-called electroviscous effect. It is well known that an electrolyte solution streaming between two charged walls shows an increase of the apparent shear viscosity. Assuming that the results obtained for plane parallel channels in a steady state by Levine et al. " may be used for the film situation, it was found that a maximum increase of about 20% can be expected for the viscosity of the solution inside the film compared to the bulk value. This electroviscous effect is expected to be important only in equilibrium films where an overlap of the electrical double layers occurs but nevertheless this phenomenon cannot explain the full discrepancy between theory and experiment. 

Figure 4.6 shows that below and above T. the apparent shear viscosity expressed by shear-stress/shear-rate takes on very hi values. Below the polymer could not be extruded within the limits of the apparatus and above T. FIFE of sufficient molecular mass is known to have mdt viscosities of above 10 Pa s Below polymorph II is a rigid crystal with practically only vibrational motion and above T. the melt viscosity is high because of entanglement of the relatively stiff long-chain molecules. 

Appendix B explains how polymer melt flow curves can be derived, and defines apparent (shear) viscosity. It is difficult to correlate the apparent viscosity with a single molecular weight average, because it depends on the width of the molecular weight distribution. However, in the limit of very low shear strain rates 7, when the entanglements between polymer chains produce negligible molecular extension, the apparent viscosity approaches a limiting value... 

The apparent shear viscosity decreases as the shear strain rate increases. 

Above all other parameters, it is the relative molecular mass of a polymer which determines the apparent shear viscosity (7.N.3). Figure 7.14 shows the stress dependence at 170°C of four BPE polymers with relative molecular masses ranging from extremely high (MFI 0.2) to extremely low (MFI200). Note that the shape of the curves (the shear thinning characteristics) is little changed by variations in relative molecular mass. 

It was obvious that the mixing torque of the NR/HDPE blends corresponded to the apparent shear viscosity curve in which the mixing torque and apparent shear viscosity of the NR/HDPE blends can be arranged in the following sequence 80/20 >60/40 >50/50 >40/60 >20/80 as shown in Figure 18.3. 

The mixing torque and apparent shear viscosity of the blends increased with increasing amounts of NR might be due to the natural characteristics of ADS that is produced from NR latex without shear cutting in the production process and it was dried at low temperature using the heat from sunshine. Therefore, ADS itself will have high Mooney viscosity in comparison with those other NR block types. 

Figure 18.22 Effect of apparent shear rate on the apparent shear viscosity of STR5L/ EPDM blends at various blend compositions.

Table 18.5 showed the power law index and the consistency of flow of STR5L/EPDM and STR5L/BEPDM blends. Shear flow curves of the pure rubbers and their blends illustrated the pseudoplastic property as shear thinning behaviour with a power law index nshear rate increased as shown in Figures 18.22 and 18.23 for STR5L/EPDM blend and STR5L/BEPDM blend, respectively. 

Figure 18.24 compares the apparent shear viscosity with the level of EPDM or BEPDM in the blend composition at the apparent shear rates of 50, 150 and... 

Figure 18.24 Comparison of apparent shear viscosity at apparent shear rates of 50, 150 and 500 s for STR5L blended with various contents of EPDM and BEPDM.

This was claimed to be attributed to the maximum compatibilizing effect or chemical interaction between PP and MNR phases at a loading level of Ph-PP of 5% w/w. Plots of apparent shear viscosity versus shear rate of 60/40 MNR/ PP blends with PP-g-MA and Ph-PP as a compatibilizer are shown in Figures 18.29 and 18.30, respectively. 

The maximum apparent shear viscosity was observed at a loading level of 5% w/w for both compatibilizers used. This trend of apparent shear viscosity was found to be the same as the apparent shear stress. 

Figure 18.29 Apparent shear viscosity at constant shear rates for simple blends of 60/ 40 MNR/PP with various quantities of PP- -MA compatibilizer.

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.

Figure 18.34 Plots of apparent shear viscosity versus apparent shear rate for MNR-STR blended with various quantities of STR 5L.

The melt rheological behaviour in terms of Mooney viscosity, apparent shear stress, and apparent shear viscosity at 100 of two types of blends that included a blend between maleated STR 5L (MNR) and cassava starch and a... 

Figure 18.40 Relationship between apparent shear rate and apparent shear viscosity of MNR blended with various quantities of cassava starch.

Figure 18.44 Relationship between apparent shear viscosity and shear rate of PMMA, NR-g-PMMA and TPVs prepared from NR-g-PMMA/ PMMA blends (60/40) at 200 °C.

Figure 4 displays the general behavior of the shear-thickening transition observed with imposed shear rate. The steady shear stress cj(7) and the steady apparent shear viscosity 17(7) are shown as a function of the applied shear rate for the hexadecyl-trimethylammonium/7-toluenesulfonate (CTAT) at c = 0.41 wt. %. For this system, the overlap concentration was estimated at c = 0.5 wt. % and the shear-thickening to be present over the range 0.05-0.8 wt. % [75,103]. 

Fig. 26 Variation of the apparent shear viscosity r] = C7st(7)/7 as a function of the shear rate for a solution of CPCl/Hex wormlike micelles in 0.2 M NaCl brine. The total concentration is c = 36 wt. % and the molar ratio [Hex]/[CPC1] = 0.49. The continuous line between the data points is a guide for the eyes. At high shear rates, the viscosity decreases according to a power law with exponent —0.73...

The statement in connection with equations 56 and 57 that simple extension gives the same information as simple shear is limited not only to materials with n very near i but also to small deformations. With large deformations and/or large rates of deformation, the two types of strain show very different behavior. For example, in steady-state flow, the apparent shear viscosity (ratio of stress to rate of strain) commonly decreases with increasing rate of strain, whereas the apparent elonga-tional viscosity may remain constant or increase. Some examples will be shown in Chapters 13 and 17. 

N Zero shear viscosity (riQ) Apparent shear viscosity rj)... 

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