Viscosity measurements extensional

Fig. 22. Schematic diagram of the opposite jets device with some of the associated streamlines (the x marks the location of the stagnation point). It has been determined that a ratio of d/(2 r0) w 1 — 1.4 constitutes the optimum geometry for extensional viscosity measurements [104]...

Underwriters Laboratory UL 94 Standard for Safety, 11 457-458 Undifferentiated chemicals, 20 712 Undiscovered petroleum resources, 18 595 Unfilled tooth restorative resins, 8 333 Uniaxial extensional viscosity, measuring, 21 740... 

Figure 3-25 A Spin-Line or Fiber-Spin Rheometer for Extensional Viscosity Measurement (Redrawn from Bames et al., 1989).

While dynamic mechanical and steady shear measurements are frequently used in rheology studies of surfactant systems, extensional viscosity measurements are lacking. This can be attributed to the difficulties associated with such measurements and the lack of commercial laboratory instrumentation since the discontinuance of the Rheometric Scientific RFX rheometer. For many detergent compositions, the relatively low viscosity further complicates such measurements. There appear to be very few data on extensional or elongation viscosity for detergent consumer products and actives in the technical literature at this time. 

A commercial instrument for extensional viscosity measurements is currently offered by the Thermo Electron Corporation [40], The device uses capillary breakup techniques and is called the Haake CaBER . Vilastic Scientific, Inc. also offers an orifice attachment to their oscillatory rheometer for extensional viscosity determinations [41,42], The principle of operation of the rheometer is oscillatory tube flow [43,44], Dynamic mechanical properties can be determined... 

FIG. 4.16 Example of an extensional viscosity measurement configuration using parallel plates. 

In marked contrast to measurements of shear rheological properties, such as apparent viscosity in steady shear, or of complex viscosity in small amplitude oscillatory shear, extensional viscosity measurements are far from straightforward. This is particularly so in the case of mobile elastic liquids whose rheology can mitigate against the generation of well-defined extensional flow fields. 

A. E. Everage and R. L. Ballman, The extensional flow capillary as a new method for extensional viscosity measurement. Nature 273, 213-215 (1978). 

Figure 3.7 Schematic diagram showing the principal features of the filament stretching method for extensional viscosity measurements (a) vertical filament stretching (b) horizontal filament stretching.

How do we measure extensional viscosity Apart from a limited number of applications where it is possible to form filaments and sheets and puU them in one or two directions, the answer is that it is much more difficult to perform extensional viscosity measurements than their shear viscosity equivalents. For polymer melts, it is possible to chiU the clamps used to hold the melt, and so secure the sample, see figure 26. Sometimes, it is even possible to use a super-glue to attach the sample to the moving clamps ... 

Even though eommereial instruments are available for making extensional viscosity measurements on polymer melts, this is not a routine measurement. The stretch-rate range of these extensional viscometers is such that the maximum stretch rate that can be achieved is of the order of 1 sec in polymer processing operations, a stretch rate of 100 sec is commonplace. Also, not every polymer stretches uniformly, and, even when it does, steady-state stress levels are not always attained. For all of these reasons, extensional viscometry is an area of current research. Additional details regarding extensional and other viscometers may be found in the book by Dealy [16]. 

Three HIPS resins possessing distinct rheological properties were utilized in this study STYRON 1200, 1170, and 484. These resins have melt flow rates (MFR) of 5.0, 2.1, and 2.8 g/10 min (200T05kg) and will be referred to in the paper as HIPS 1, HIPS 2, and HIPS 3, respectively. The dynamic mechanical spectroscopy measurements (viscosity vs. frequency and temperature, loss and storage modulus vs. frequency and temperature) were performed on a TA Instruments ARES rheometer. The measurements were obtained at three different temperatures 170, 190, 210, and 2301C. The uniaxial extensional viscosity measurements were performed at three Hencky rates 0.1, and 10s on a SER (Sentmanat Extensional Rheometer, Xpansion Instruments) at 1701C. 

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. 

Extensional viscosity measurements were determined at 180°C and different extension rates using an Exteitsional Viscosity Fixture (EVF) irrstalled in the ARES-LS rheometer. The linear viseoelastie (LVE) envelope was determined by a step-strain experiment at low strain rates and converted to the zero-exterrsion rate based on the Trouton s rule. 

Extensional viscosity measurements were determined at 180°C and 1 sec extension rates using the Extensional Viscosity Fixture (EVF) placed in the ARES-LS rheometer. 

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