Pseudo-Newtonian region

Polyester BB1 was run twice in steady mode at 290°C (Figure 10), and shows that the orientational effect of the first run has a drastic effect on steady shear viscosity. In the first run the log viscosity vs. log shear rate had a slope of -0.92 (solid like behaviour, yield stress), but in the second run a pseudo-Newtonian plateau was reached from approx. 1 sec 1. Capillary viscosity values corresponded reasonably well with the second run steady shear data. The slope at high shear rates was close to -0.91 which corresponds nicely to the first-run steady shear run. All this could suggest, that this system is not completely melted, but still has some solid like regions incorporated. At 300°C capillary viscosity data showed an almost pseudo-Newtonian plateau. This corresponds quite well to the fact that fiber spinning as mentioned earlier was difficult and almost impossible below 290°C, but easy at 300°C. At an apparent shear rate of 100 sec 1, a die-swell was found to be approximately 0.95. 

Nonhydrodynamic effects of filler particles (e.g., filler networking) dominate the low shear behavior in such a manner that an apparent yielding region overrides the pseudo-Newtonian plateau of the polymer matrix (corresponding to parameter TI02)... 

The Maxwell model can successfully describe monoexponential stress relaxation properties. This holds for the regime of small deformations, shear rates, or shear stresses. In the region of elevated mechanical forces, severe departures from simple Newtonian and Hookean occur. In viscoelastic surfactant solutions, it is often observed that the shear viscosity decreases markedly with increasing amount of shear. This t3q)ical behavior is called shear thinning or pseudo plastic. The non-Newtonian behavior of such solutions is of great practical interest, and it is intimately connected with orientation processes or structural changes that occur during flow. 

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