Extrusion rheological curves

Fig. 11.2 The effect of the PP controlled rheology (CR) or viscracking process on the viscoelastic grid each curve represents a PP macromolecular degradation path. [Reprinted by permission from R. C. Kowalski, Fit the Reactor to the Chemistry, in Reactive Extrusion, M. Xanthos Ed., Hanser, New York, 1992.]...

When assessing the rheological behavior of PA/PO blends, a strong effect of shear forces upon should be considered. The reason is a qualitative difference between the flow curves for PO and PA. Aliphatic PAs show an extended Newtonian plateau typical of polymers with a narrow MWD (71). PA6, for instance, can retain the Newtonian pattern of flow (72) up to a shear rate of 10 s . The curve describing the relationship of rj versus y for PO is typical of polymers with a wide MWD the anomaly in viscosity ( j decreases with increase in the shear rate) was observed at a much lower shear rate of < 10 s . That is why the effects of viscosity s growth—in the case of PA6/PO compatibilized blends—manifest themselves to the utmost at relatively low shear rates, upto 10 s . Such shear rates are typical of extrusion of polymer materials (72). 

Keywords peroxide, molar weight distribution (MWD), rheology, crystallization, extrusion, melt flow index (MFI), controlled rheology (CR), peroxide-degradation, residence time distribution (RTD), halflifetime of peroxides, melt elasticity, die swell, viscosity curve, shear rate, elongational viscosity, melt fracture, heterophasic PR... 

The rheological behaviour of the fluid polymer is indicated by the flow curves T = /(y), Figure 3.249. Figure 3.249, plotted for the increasing and decreasing shear stresses, show the appearance of two distinct curves resulting from the existence of a tixotropy phenomenon. The structure of the melt changes under the action of extrusion forces. 

---