Extensional Flow Properties

There are many practical situations in which extensional flow properties are important, both in processing detergent compositions and during consumer use. One of the most problematic can be the filling operation where a clean separation of the fluid and the filling nozzle does not occur. When extensional viscosity is... 

Extensiometer n. A rheometer for measuring the extensional flow properties of molten polymers. In one early form, the Cogswell rheometer, useful at tensile viscosities over lO Pa/s, unidirectional tensile force was exerted on a polymer rod by a dead-weight acting through a cam and pulley. As the cam rotated, the moment arm exerted... 

Interest in the study of the extensional flow properties of polymer melts also stems from the fact that several industrially important, polymer processing operations such as fiber spinning, blow molding, and film blowing involve a predominantly extensional mode of deformation. In each of these processes a material experiences large and time-dependent stresses the theoretical prediction of these stresses is a necessary prerequisite for the rational design of any useful control strategy. 

Chapters 6 to 9 discuss the steady shear viscous properties, steady shear elastic properties, unsteady shear viscoelastic properties and extensional flow properties, respectively. The effect of filler type, size, size distribution, concentration, agglomerates, smface treatment as well as the effect of polymer type are elucidated. The tenth chapter has been... 

The limited information on the extensional flow properties of filled polymer systems does not leave much room for extensive discussion on this subject. Thus, fliis chapter is ratiier restricted and though the... 

The effect of filler type, size, concentration, size distribution, agglomerates, surface treatment and polymer matrix on the rheology of the filled systems is discussed in detail in most cases. Only where information is lacking, such as in tire case of extensional flow properties in Chapter 9, are some of tiie effects missing, and the discussion is concise on the treated effects. 

Lagendijk, R. R, Hogt, A. H., Buijtenhuijs, Gotsis, A. D. Peroxydicarbonate modification of polypropylene and extensional flow properties. Polymer (2001) 42, pp. 10035-10043... 

We have seen that rheometers capable of accurate measiuements of extensional flow properties are limited to use at low Hencky strain rates, usually well below 10 s . In order to reach higher strain rates, the drawdown of an extruded filament ( melt spinning ) and the converging flow into an orifice die or capillary have been used to determine an apparent extensional viscosity . Since the stress and strain are not imiform in these flows, it is necessary to model the flow in order to interpret data in terms of material functions or constants. And such a simulation must incorporate a rheological model for the melt under study, but if a reliable rheological model were available, the experiment would not be necessary. This is the basic problem with techniques in which the kinematics is neither controlled nor known with precision. It is necessary to make a rather drastically simplified flow analysis to interpret the data in terms of some approximate material function. 

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