Apparent shear rate, capillary rheometer measurement

A slit die is designed on the assumption that the material is Newtonian, using apparent viscous properties derived from capillary rheometer measurements, at a particular wall shear stress, to calculate the volumetric flow rate through the slit for the same wall shear stress. Using the correction factors already derived, obtain an expression for the error involved in this procedure due to the melt being non-Newtonian. Also obtain an expression for the error in pressure drop calculated on the same basis. What is the magnitude of the error in each case for a typical power law index n = 0.377... 

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 measured values of polymer flow taken by capillary rheometers are often presented as plots of shear stress versus shear rate at certain temperatures. These values are called apparent shear stress and apparent shear rate at the tube wall. Corrections must be applied to these values in order to obtain true values. The corrected value of shear stress is determined by the Bagley correction [20]... 

Measured with a capillary rheometer. The apparent shear rate was about 8.9 s (high-temperature crystal). 

A capillary rheometer Rosand 700 was used to measure the pressure drop and flow rate in a die having diameter D=1 mm, aspect ratio of L/D=16 and 180° entiy angle. The apparent shear rate,, and nominal... 

The wall slip measurements were carried out on the same capillary rheometer at 180°C according to the Mooney method [12]. Three dies having 1.0, 1.5 and 2.0 mm diameter and L/D=16 are used to record the wall shear stress at apparent shear rates within 20-100 s. If the die radius is R, the true slip free shear rate is Yj, the slip velocity is U, the volume flow rate, Q, through the die is given by the following equation [13] ... 

Shear viscosity-shear rate curves were measured using a Goettfert Rheograph 6000 triple bore capillary rheometer at 210°C. A die of 30/1 aspect ratio and 180° entrance angle was used. Apparent values were determined by controlling the drive speed and recording the entrance pressure. No corrections were made to the data to determine the Bagley and Rabinowitch factors. 

The shear viscosity at apparent shear rates ranging from 20 to 5000 s was measured on a two bore high precision capillary rheometer (Rosand RM - 700), equipped with a 1 imn diameter die with L/D = 16 and 180° entry angle. A zero length die with 1 mm diameter and 0.25 mm length was used for making the entrance pressme drop correction. 

In order to facilitate rapid melt viscosity measurement and data analysis a modified Gflttfert capillary rheometer has been interfaced to a Hewlett-Packard data acquisition system. All test parameters (temperature, barrel pressure, etc) are monitored automatically and the data is stored on magnetic tape. After testing is complete, raw data is entered into an analysis program used to compute tables and draw plots of shear stress, shear rate, and apparent viscosity. Examples of the application of this system to commercial polymers are discussed. 

FIGURE 6.28 Apparent viscosity of a blend of EPDM with a fluoroelastomer measured in a capillary rheometer at a shear rate equal to 14 s (Shih, 1976). 

The temperature dependence of the apparent melt viscosity of pure HP-LCP significantly differs from that of pure LCP-E. The melt viscosity of pure HP-LCP and pure LCP-E were measured by a Capilograph-IB capillary rheometer (Toyo Seiki Seisaku-sho, Ltd.) which can detect the shear rate and shear stress of molten polymer flowing out of the capillary. The geometry of the capillary die used in this measurement was 0.5 mm in diameter and 10 mm in length. 

Caoillarv rheometrv Apparent viscosities of PLA/IL-1, PLA/IL-2 compounds were determined using a capillary rheometer (Instron, Model 4204) in the shear rate range of 15 s to 38 s at 190°C. A melt flow indexer (Tinius Olsen, Model UE-4-78, Willow Grove, PA) was also used to measure flow characteristics at 2060g, 190°C. 

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