Rheological measurements capillary rheometer

Rheological measurements on the slurry have been performed by Bohlin rheometer model VOR and constant stress rheometer C.. These two units combined are powerful enough to analyze slurries completely in viscometry, oscillatory and relaxation tests. Injection molding compound is fully characterized rheologically using capillary rheometer. 

Capillary rheometers are in the form of a barrel where the operator puts the polymer sample. After heating to equilibrate its temperature, the sample is pushed by a piston through a die at chosen rates. Various sizes and shapes of dies are available. Capillary rheometers measure the rheological properties under broad ranges of conditions of temperature, pressure, stress, strain and time, allowing the adoption of parameters near to those for processing. 

There are a number of techniques that are used to measure polymer viscosity. For extrusion processes, capillary rheometers and cone and plate rheometers are the most commonly used devices. Both devices allow the rheologist to simultaneously measure the shear rate and the shear stress so that the viscosity may he calculated. These instruments and the analysis of the data are presented in the next sections. Only the minimum necessary mathematical development will he presented. The mathematical derivations are provided in Appendix A3. A more complete development of all pertinent rheological measurement functions for these rheometers are found elsewhere [9]. 

Melt flow rheology measurements were obtained on the MBAS polymer using an Instron capillary rheometer. The data reported were obtained using an 0.056-inch capillary, 90° included angle, with an L/D of 36. In Figure 5 the maximum shear stress (lb/in2) is plotted vs. the apparent shear rate (sec 1). The apparent viscosity (lb-sec/in2) vs. tem-... 

The rheological behaviour of the two polymers was determined using classical techniques of rheometry, already described in Chapter II. 1 (rotational and capillary rheometers for shear viscosity and first normal stress difference measurements CogsweU method for the elongational viscosity). 

Among the many different classes of thermotropic polymers, only a limited number of polyesters based on aromatic ester type mesogenic units have been studied by rheological methods, beginning with the publication by Jackson and Kuhfuss of their work on the p-oxybenzoate modified polyethylene terephthalate, PET, copolymers. They prepared a series of copolyesters of p-hydroxybenzoic acid, HBA, and PET and measured the apparent melt viscosity of the copolymers as a function of their composition by use of a capillary rheometer. On inclusion of low levels of HBA into PET, the melt viscosity increased because of partial replacement of the more... 

Jerman and Baird recently conducted rheological studies on the same copolymers using an Instron capillary rheometer. They also measured die swell and entrance pressures. They observed that the viscosity of the 60 mole % HBA/PET copolymer was two orders of magnitude lower than that of PET when compared at the same temperature of 285 °C, which is similar to the results reported earlier by Jackson and Kuhfuss Die swell of the copolymers was highly temperature dependent. In general,... 

The capillary rheometer is a valuable tool for predicting the processability of thermoplastic resins. This is done by measuring melt viscosities at shear rates and temperatures commonly encountered in extrusion and injection molding. This procedure is difficult and time consuming due to the complex nature of rheological measurements and analyses. An automated system for acquisition and analyses of capillary rheometer data has been developed to speed up and simplify this important analytical technique. 

Standards for the chemoviscosity of reactive fluids are shown in Table 4.5. Clearly these tests mainly are typical of rapid, quality-control measurements however, in contrast the standard proposed by Rydes (1993) for using capillary and slit-die rheometry is based on true rheological analysis. Alternative rheometers used for reactive systems are summarized in detail in Table 4.6. 

Rheological and Tensile Properties. Melt rheological measurements were made on an Instron Capillary Rheometer (0.993" L X 0.05014" D) at a temperature of 200°C and at various shear rates corresponding to crosshead speeds of from 0.005 in./min to 20 in./min. Measurements were also made with an Instron TM Model (0.05034" D X 1.0074" L) at 200°C and at various shear rates corresponding to crosshead speeds of from 0.006 in./min to 10 in./min. 

Capillary Rheometer and an Extruder Are They in Agreement One can ask a reasonable question If rheology data are obtained in a capillary rheometer, are they applicable to an extruder To answer this question, at least for a specific set of conditions, a direct comparison was made [31]. It was found that the capillary rheometer and extruder are in good agreement for neat plastics (polystyrene and polypropylene), but extruder systematically measures lower viscosities in glass-fiber-filled plastics. 

A systematic study of the basic rheological properties for a wide variety of polypropylene melts has been made by Minoshima et al. [89]. These authors measured shear viscosities at low shear rates in a Rheomatrics mechanical spectrophotometer and at high rates in an Instron capillary rheometer. The principal normal stress difference, Ni, was measured in the mechanical spectrophotometer with a cone and plate device. The elongational viscosity, of special importance to fiber formation, was measured in an apparatus built by Ide and White [90],... 

The capillary rheometer, one the oldest and most widely applied experimental tools for measuring the viscosity of fluids (Fig. 15), was used extensively on almost all classes of complex fluids by the founders of modern rheology during the 1920s and 1930s. Its application to rubber dates to the work of Marzetti [M8-11] and Dillon and coworkers [D7-9], and it has been widely used through the years. 

ASTM D3835/2000 test method measures rheological properties of thermoplastic (and thermosetting) melts by using a capillary rheometer [4], The test method includes measurements of viscosity, shear rate, shear stress, swell ratio, and percent of extrudate swell. Assuming a newtonian fluid, to calculate melt viscosity j, use... 

An Instron capillary rheometer (Model 3211) was used to measure the rheological properties. A capillary die of diameter D=0.00127m and a length to diameter ratio, L/D, of 28.7 was used. Measurement was done at 330 X and 350 °C for all PAI-l/LCP blends, but only for the 10% and 25% LCP concentration blends with PAI-2 since at all other concentrations a poor mixing was noticeable. 

Rheological characterization, which wonld include measurement of compound viscosity using a Mooney Viscometer, indicating ease of processing, vulcanization and curing kinetics, and rheological information obtained from a capillary rheometer. 

Rubber particle-size distribution is usually measured with a Coulter coimter or directly from electron photomicrographs (110,343) the latter also gives details of particle morphology. Rheological studies are made with a modified tensile tester with capillary rheometer (ASTM D1238-79) or with the powerful Rheometrics mechanical spectrometer (344). For product specifications, a simple melt-fiow test is used (ASTM D1238 condition G) with a measurement of the heat-distortion... 

Some type of melt viscosity is included in the specification for almost every polymeric or plastic product. This is because viscosity is related to the molecular weight and to the performance of a polymer. Equipment used for rheological measurements range from the simple and ubiquitous melt flow indexer to the precise and quantitative capillary and cone-and-plate rheometers. 

Rheology studies the relationship between force and deformation in a material. To investigate this phenomenon we must be able to measure both force and deformation quantitatively. Steady simple shear is the simplest mode of deforming a fluid. It allows simple definitions of stress, strain, and strain rate, and a simple measurement of viscosity. With this as a basis, we will then examine the pressure flow used in capillary rheometers. 

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