Parallel plate rheometers

Flowability of plastics is largely determined by the dependence of viscosity on shear rate. Viscosity of water, for example, does not change with shear rate. When water moves through a capillary, fast or slow, its viscosity is same. In a forced oscillation rheometer, parallel plates immersed in water can move fast or slow, but the viscosity of water remains still the same. Therefore, a plot of viscosity against shear rate looks as a flat straight line, parallel to the horizontal axis (Fig. 17.1). 

Three useful tests have been used to evaluate the working and setting properties of experimental cements. These are the parallel plate plas-tometer, the penetrometer and the oscillating rheometer. They are described in the following sections of this chapter. 

ISO 6721-8 1997 Plastics - Determination of dynamic mechanical properties - Part 8 Longitudinal and shear vibration - Wave-propagation method ISO 6721-10 1999 Plastics - Determination of dynamic mechanical properties - Part 10 Complex shear viscosity using a parallel-plate oscillatory rheometer ISO 9311-2 2002 Adhesives for thermoplastic piping systems - Part 2 Determination of shear strength... 

This section describes common steps designed to measure the viscosity of non-Newtonian materials using rotational rheometers. The rheometer fixture that holds the sample is referred to as a geometry. The geometries of shear are the cone and plate, parallel plate, or concentric cylinders (Figure HI. 1.1). The viscosity may be measured as a function of shear stress or shear rate depending upon the type of rheometer used. 

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). 

FIGURE 10.11 Scheme of the rheometer in the parallel plates configuration. 

Rheological measurements were carried out at a Dynamic Analyzer Rheometer RDA II from Rheometrics. Parallel plate geometry with a plate diameter of 25 mm was used to perform the tests where thin films of materials of 1 mm thickness were inserted. To ensure the viscoelastic... 

Using a thermomechanical analyzer (TMA) as the parallel-plate rheometer, the neat resin was laminated under identical conditions as did the prepreg to deteraiine the viscosity history. Throughout this study, the quartz probe (0.145 in. in diameter) which is attached to a linear variable differential transfomier for thickness monitoring exerted a constant force of 2... 

The experimental device constructed to orient uniformly thick samples in simple shear is schematically represented in Fig. 3. It is basically a sliding-plate rheometer, the polymer sample being sheared between two temperature-controlled parallel plates. The upper plate is fixed whereas the lower plate can be displaced both horizontally and vertically with two pneumatic jacks. 

Viscoelastic measurements in oscillatory shear were performed using a Rheometrics System Four rheometer in the frequency range 10 3 rad/sec < co < 102 rad/sec. 8 mm diameter parallel plates were used for temperatures below 80°C and 25 mm diameter parallel plates were used for T>80°C, with plate separations of 1.1 0.2 mm. Comparison of... 

Talc filled thermoplastic materials were studied in rheometers of different geometries (elongational, capillary, parallel plate). Geometry of the testing method and the flow paths had an important influence on the orientation of talc particles. In addition to flow decrease, an increased concentration of filler had a pronounced effect on both flow and orientation. The cross-sectional distribution of particles de-... 

Rheology Rheological measurements were performed at 25°C with an ARES 2 KFRT controlled strain rheometer (Rheometric Scientific). For the measurements parallel plates of 50 mm diameter were used. The gels were loaded between the plates (2-mm gap) and allowed to rest for 3 min. A strain sweep (0.1 to 100%) was performed at 1 Hz frequency to determine the range of viscoelasticity for each sample and a 2% strain was selected for all samples. A frequency sweep test (0.1 to 16 Hz) was then performed. Samples of 30 and 50% s/w concentration could not be analyzed because of the difficulty in obtaining samples of proper and constant geometry. 

Capillary rheometry and parallel-plate rheometry use the fact that wall slip will manifest itself as a geometry-dependent phenomenon. That is, wall slip will appear as a geometric effect on apparent rheological properties. In the capillary-rheometer technique, slip will manifest itself as an effect of capillary diameter ( )) on the shear stress (t, ). Wall slip in capillary rheology can be calculated from an analysis that involves the following ... 

The most common measuring systems used for the effects of shear rate on the chemo-viscosity of thermosets have been the parallel-plate rheometer and the capillary rheometer however, the choice of rheometer is dependent on the type of system to be studied. The advantages and limitations of these systems are presented in Table 4.6. 

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