Rheology extensional rheometry

However, recent publications are indicating a switch to describing dough quality by dough rheology, including extensional rheometry. Some of these rheology-based methods are summarized below. 

The comparatively less elastic nature of many food products makes the analyses of extensional rheology data easier than has been possible with polymeric fluids. This relative ease of data interpretation provides an opportunity both for learning the extensional behavior of materials and for effective application of extensional rheometry in the food industry. 

V. S. Au-Yeung and C. W. Macosko, Extensional rheometry of several blow molding polyethylenes, Proc. Vlllth Int. Congress on Rheology, Naples, Italy, 3, pp. 717-722 (1980). 

Chapters 5-7, which describe shear and extensional rheometry, give the most important deformation geometries and derive the working equations for each. These equations permit conversion of measured quantities like force, torque, pressure, and angular velocity to stress and strain on the sample. Such stress and strain data allow us to determine rheological material functions, which are needed to evaluate the parameters in particular constitutive equations. 

Chapter 3 deals with rheometry which is the method of measurement of the various rheological parameters described in Chapter 2. The rheometers may be of Ae rotational type or the capillary type for shear flows and the shear free t)rpe for extensional flows. 

In recent times, the introduction of more sophisticated rheological methods and especially the ability to determine independently the shear and extensional viscosity of polymer melts, the design and correlation between molecular structure and rheology has been more accessible to industrial practitioners. Processes such as extrusion blow molding involve those types of deformations such as shear and extension, which can be determined using capillary rheometry and extensional viscosity measurements, which can be related to the formation and blowing of the parison. 

---