Polymer rheology parallel plate

Experimentally, the dynamic shear moduli are usually measured by applying sinusoidal oscillatory shear in constant stress or constant strain rheometers. This can be in parallel plate, cone-and-plate or concentric cylinder (Couette) geometries. An excellent monograph on rheology, including its application to polymers, is provided by Macosko (1994). 

Fig. 4.35 Phase angle as a function of reduced frequency, determined from parallel plate rheology experiments, for a PS-PI diblock (Mv = 130kgmol, 50wt% PS) in dioctyl phthalale at a concentration 24.7 wt% polymer (Jin and Lodge 1997).

It is well known in polymer rheology that a torsional parallel-plate flow cell develops certain secondary flow and meniscus distortion beyond some stress level [ 14]. For viscoelastic melts, this can happen at an embarrassingly low stress. The critical condition for these instabilities has not been clearly identified in terms of the shear stress, normal stress, and surface tension. It is very plausible that the boundary discontinuity and stress intensification discussed in Sect. 4 is the primary source for the meniscus instability. On the other hand, it is well documented that the first indication of an unstable flow in parallel plates is not a visually observable meniscus distortion or edge fracture, but a measurable decay of stress at a given shear rate [40]. The decay of the average stress can occur in both steady shear and frequency-dependent dynamic shear. 

Parallel-plate rheometers are often more useful for studying rheology of filled polymers or composite materials, particularly when the size of the fillers is comparable fo fhe disfance between the truncated cone and the surface of the plate. Again, the torque M and the normal force N tending to separate the two plates are measured. In steady-shear flow, the shear rate and the shear stress at the edge of the disks located atr = R are given by... 

The cone-and-plate and parallel-plate rheometers are rotational devices used to characterize the viscosity of molten polymers. The type of information obtained from these two types of rheometers is very similar. Both types of rheometers can be used to evaluate the shear rate-viscosity behavior at relatively low vales of shear rate therefore, allowing the experimental determination of the first region of the curve shown in Figure 22.6 and thus the determination of the zero-shear-rate viscosity. The rheological behavior observed in this region of the shear rate-viscosity curve cannot be described by the power-law model. On the other hand, besides describing the polymer viscosity at low shear rates, the cone-and-plate and parallel-plate rheometers are also useful as dynamic rheometers and they can yield more information about the stmcture/flow behavior of liquid polymeric materials, especially molten polymers. 

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... 

Mutel, A.T. and Kamal, M.R. (1986) Qiaracterization of the rheological behavior of fiber-filled pol3 ropylene melts imder steady and oscillatory shear using cone-and-plate and rotational parallel plate geometry, Polym. 

Kataoka, T., Kitano, T. and Nishimura, T. (1978) Utility of parallel-plate plastometer for rheological study of filled polymer melts, Rheol Acta, 17, 626-31. 

Mutel, A. T. and Kamal, M. R., Characterization of the rheological behavior of fiber-filled polypropylene melts under steady and oscillatory shear using cone-and-plate and rotational parallel plate geometry, Polym. Compos., 1, 283-294 (1986). Sacks, M. D., Khadilkar, C, S., Scheiffele, G. W., Shenoy, A. V., Dow, J. H., and Sheu, R. S., Dispersion and rheology in ceramic processing, Adv. Ceram., 24, 495-515 (1987). 

H. -T. Chiu, and J. -H. Wang. A study of rheological behavior of a polypyrrole modified UHMWPE gel using a parallel plate rheometer. Polymer Engineering... 

A.T. Mutel, M.R. Kamal. The effect of glass fibers on the rheological behavior of polypropylene melts between rotating parallel plates. Polym. Compos., 5 (1), 29-35,1984. 

Melt rheology offers a spectrum of information about the polymer (or blend), its thermal stability, shear sensitivity, the mechanism of degradation (e.g., chain scission vs. branching and crosslinking), processability, etc. The preferred method of testing is dynamic between cone-and-plate or parallel plates. ... 

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... 

The rheological behaviour of molten polymers is of prime importance as it relates to their microstructure and governs their processing characteristics [1]. Rotational rheometers, specifically cone-plate, parallel plate, and sliding plate rheometers are routinely used to characterize the linear viscoelastic properties of polymer melts. Small amplitude oscillatory shear experiments are employed to measure the storage (G ) and loss moduli (G"), which are related to the elastic and viscous character of the material, respectively, and the complex viscosity (77 ) as functions of angular frequency (a). 

A polymer solution (of density 1000 kg/m ) is flowing parallel to a plate (300 mm x 300 mm) the free stream velocity is 2 m/s. In the narrow shear rate range, the rheology of the polymer solution can be adequately approximated by both the power-law (m = 0.3 Pa-s" and n =0.5) and the Bingham plastic model (tq = 2.28 Pa s and /xg = 7.22 mPa-s). Using each of these models, estimate and compare the values of the shear stress and the boundary layer thickness 150 mm away from the leading edge, and the total frictional force on each side of the plate. 

Capillary rheometers are the most widely used rheological instruments for polymer melts. They are, however, generally limited to rather high shear rates. Rotational rheometers can provide data at lower shear rates. Cone-plate and parallel disc instruments have been popular with thermoplastic melts. Pressurized instruments, such as biconical or Mooney shearing disc instruments, are used with elastomers to prevent slippage [39]. Sandwich rheometers are used at the lowest shear rates and shear stresses. 

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