Bagley corrections

Viscosities of the blends and composites were measured in shear flow with a Gottfert Rheograph 2002 capillary viscosimeter. The shear rate was investigated from 100-10000 s" . The L D ratio of the capillary die was 30 mm 1 mm. Rabinowitch correction was made to the measurements, but Bagley correction was not applied. 

The pressure change due to the entry effects for a set of experiments is the intercept Affl obtained through linear regression of the AP data as a function of L/R. This intercept APo is then subtracted from the measured pressure to obtain the correct pressure change, AP,. This pressure correction is known as the Bagley correction. The slope of the regression analysis from Fig 3.17 can be used to obtain the stress at the capillary wall, r , as follows ... 

Next the pressure change across the different capillaries must be calculated and corrected for the end-effect pressure loss using a Bagley correction. 

Person 1 Estimate the entrance region pressure drop, APgm, using the Bagley correction. What can you say about the percentage of the entrance pressure drop relative to the total pressure drop ... 

Finally, because the results obtained in capillary viscometry, especially for capillaries of small UR, are influenced by both extensional and shear flow phenomena associated with the fluid spatial accelerations at the capillary entrance, it is necessary to correct the values of tw given in Eq. E3.1-3. Chapter 13 covers the nature, magnitude, and significance of these, commonly known as Bagley corrections. 

Entrance and Exit Capillary Pressure Losses the Bagley Correction... 

If the melt is non-Newtonian, corrections have to be made, the Bagley correction and the Rabinowitz correction. 

T is the shear stress (using the Bagley correction), Y is the apparent shear rate. 

Fig 24 compares experimental entrance pressure losses of LLDPE obtained using Bagley correction and numerical results obtained with the three models, but using diSerent methods. 

Open symbols numerical computation of Filled symbols numerical Bagley corrections ... 

In axisymmetric flow situations, the global pressure drop in a capillary rheometer is well described by the three constitutive equations. If one focuses on the entrance pressure drop, the numerical entrance pressure drop related to Bagley correction is foimd to be less important than the corresponding experimental data for the differential models for LDPE and LLDPE melts. For the Wagner integral constitutive equation, the computed entrance pressure drops are found to be lower for both fluids, but the computed values are closer to the experimental data for LLDPE than those related to the LDPE melt. This descrepancy, previously reported in the literature, needs further investigation. 

The capillary flow. The Interlayer slip, apparent In unconpatlblllzed blend, BL, disappeared upon addition of EP-1 or EP-2. As shown In Fig. 21 the slip affected the entrance-exit pressure drop, P, ("Bagley correction") more than viscosity. 

Bacteria, 418 Bagasse flber, 83, 86 Bagley Correction Factor, 630 Bakelite, 78 Balusters, 42, 429 Bamboo flber, 90... 

Of course, polymier melts are non-Newtonian due to their shear-thinning behavior. The value calculated from Eq. (6.1) must be corrected for the shear rate at the wall, which is higher for a polymier melt than that calculated by Eq. (6.1). This method is known as the Rabinowitsch correction and is based on determination of viscosity at a location inside the flow channel as opposed to the wall. At a representative location, Newtonian and non-Newtonian shear rates coincide. This location is at r = nR/4, where the pressure transducer should be located to measure the pressure drop. Another correction has to be made for other pressure losses it is called the Bagley correction. PI... 

Four measures of melt elasticity have been used the first normal stress difference, Nj, the storage modulus, G , and the two indirect ones, the entrance-exit pressure drop, P. (or Bagley correction), and the extrudate swell, B. In homogeneous melts, the four measures are in a... 

Further consequences of the yield stress [i.e., the plug flow] are (i) a drastic reduction of the extrudate swell, B = d/d (d is diameter of the extrudate, d that of the die) [see, e.g., Crowson and FoUces, 1980 Utracki et al, 1984], and (ii) significant increase of the entrance-exit pressure drop, Pg (also known as Bagley correction). For single-phase fluids, these parameters have been related to elasticity by molecular mechanisms [Tanner, 1970 Cogswell, 1972 Laun and Schuch, 1989]. However, in multiphase systems, both B and P depend primarily on the inter-domain interactions and morphology, not on deformation of the macromolecular coils. Thus, in multiphase systems [i.e., blends, filled systems, or composites], only direct measures of elasticity, such as that of Nj, or G should be used. It is customary to plot the measure of the elastic component versus that of the shear components, viz., vs. 

Avrami equation Bagley correction Barrier properties... 

As mentioned earlier, calculations from measurements are always made on the basis of Newtonian behaviour. This results in apparent quantities which have to be corrected. These corrections are necessary because of the reduced wall adhesion of many polymers (especially with a large filler content), and to this end the Rabinowitsch correction is applied to the shear rate. Also, owing to pressure losses on entry into the capillaries (when measuring with a capillary viscometer), the Bagley correction is applied to the shear stress T. 

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