Cone-and-Plate Rheometry

The rotational viscosity method described above to measure working life or pot life is a form of rheological measurement of cure. However, cone and plate rheometry is preferred for accurate measurements because the specimen size and geometry are similar to those that occur in an adhesive joint. 

Britton MM, Callaghan PT (1997a) Nuclear magnetic resonance visualization of anomalous flow in cone-and-plate rheometry. J Rheol 41(6) 1365-1386... 

Figure 5.15 gives logA j versus logy plots for an LDPE at three different temperatures, which were obtained, via Eq. (5.64), from the Pp j, measurements given in Figure 5.14. Later in this chapter we compare the values of determined from continuous-flow capillary rheometry with those obtained from cone-and-plate rheometry.

These functions have also been measured by cone-and-plate rheometry. Sample experimental data for the stress growth and stress relaxation functions can be found in chapter 3 of ref. 5, as well as for the other rheometric experiments shown in Figure 2. The analysis of the rheometric equipment used in these tests is discussed in chapter 10 of ref. 5 as well as in ref. 4. 

Mechanical rheometry requires a measurement of both stress and strain (or strain rate) and is thus usually performed in a simple rotating geometry configuration. Typical examples are the cone-and-plate and cylindrical Couette devices [1,14]. In stress-controlled rheometric measurements one applies a known stress and measures the deformational response of the material. In strain-controlled rheometry one applies a deformation flow and measures the stress. Stress-controlled rheometry requires the use of specialized torque transducers in conjunction with low friction air-bearing drive in which the control of torque and the measurement of strain is integrated. By contrast, strain-controlled rheometry is generally performed with a motor drive to rotate one surface of the cell and a separate torque transducer to measure the resultant torque on the other surface. 

Example 3.2 Cone-and-Plate Flow Rheometry The cone-and-plate flow apparatus is shown schematically in Fig. E3.2a. The polymer melt flows in the space formed by the rotating cone and stationary plate. 

Yiscometry (using coaxial cylinder, cone and plate and vane rotational viscometers, and controlled stress capillary viscometers) can be used for soft cheeses. Lubricated squeezing flow rheometry is particularly useful for measuring cheese meltability. 

Rheometrv. The following rheometers were used in this study An Instron capillary rheometer, a Rheometries mechanical spectrometer, used in both cone and plate mode as well as in the biconical mode, and a Brabender Plastograph (4). 

Mutel, A.T. Kamal, M.R. (1986). Characterization of the Rheological Behavior of Fiber-Filled Polypropylene Melts under Steady and Oscillatory Shear using Cone-and-Plate and Rotational Parallel Plate Rheometry. Polymer Compwsites, Vol.7, No.5, pp. 283-294ISSN0272-8397... 

Typically, simple shear flow is generated in cone-and-plate, plate-plate, or couette devices. Simple extensional flow is generated by devices in which a cylindrically shaped specimen is deformed in such a manner that the length increases exponentially with time. Th ogic of rheometry is reviewed and discussed in... 

Dynamic mechanical analysis in the rheology mode (oscillatory rheometry in cone and plate or parallel-plate geometries see Fig. 5.50) can be used to... 

While the cone and plate geometry is the preferred arrangement to obtain the steady viscometric functions, it is limited to low shear rates — usually, to those less than 10 s . At higher shear rates encountered in processing ( 10-10 s ), it is customary to resort to capillary rheometry to measure the shear viscosity. Unfortunately, the normal stress differences cannot be obtained from this test. To get N at high shear rates one can, however, employ a slit device based on the so-called hole pressure effect [21]. 

A.T. Mutel, M.R. Kamal. Characterization of the rheological behavior of fiber-filled polypropylene melts imder steady and oscillatory shear using cone-and-plate and rotational parallel plate rheometry. Polym. Compos., 7 (5), 283-294, 1986. 

In order to characterize the rheological properties of a polymer melt over a very large range of shear rates, data obtained in mnltiple rheometer contignrations are typically combined. Cone-and-plate and parallel plate shear measnrements are, for example, the most accurate at low shear rates. However, the shear rates accessible in a capillary rheometer are well above those that can be achieved in any other configuration. Capillary rheometry, cone-and-plate shear, and parallel plate shear rheometry provide complementary information abont polymer flow response. In the example shown in Figure 8.14, an uncross-linked silicone rnbber was measnred nsing three... 

FIGURE 8.14 Comparison of Cross model prediction with experimental viscosity data for a high-molecular-weight poly(dimethylsiloxane) using parallel plate, cone-and-plate, and capillary flow rheometry at 23°C. The fitted parameters are A, = 34.5 s, = 0.604, and t (, = 98.0 kPa s. 

Schweizer, Th. Comparing cone-partitioned plate and cone-standard plate shear rheometry of a polystyrene melt. /. Rheol (2003) 47, pp. 1071-1085... 

When compared to standard (open cavity) cone-plate or parallel disks rheometers, closed cavity torsional rheometers such as the RPA or the PPA have unique high-strain capabilities, which prompted us to modify the instmment in order to investigate the promises of FT rheometry, as outlined a few years ago by the pioneering works of Wilhelm. The technique consists of capturing strain and torque signals and in using FT calculation algorithms to resolve it into their harmonic components, as detailed below. 

FIGURE 3. Data obtained on non-Newtonian viscosity of an aqueous solution of hexylethylcellulose by four different viscometric methods capillary rheometry, concentric cylinder, cone-plate and parallel disk. 

---