A general analysis allowing the determination of shear rate and viscosity from batch mixer rotor speed and torque data is presented. The batch mixer was represented by two effective adjacent sets of concentric cylinders exerting the same torque as that obtained from the batch mixer. The effective internal radius was determined through a general procedure for calibration using non-Newtonian fluid. The effective equivalent internal radius, Ri, was determined for different polymers and processing conditions. The results revealed that Ri is a universal quantity practically insensitive to the nature and to the rheological behavior of the fluid under mixing. In the case of small gaps, it was found that there is a special position in the gap where the effective internal radius, the shear rate and viscosity are independent of rheological characteristics of the fluid under mixing. This validates the Newtonian approximation previously used by Goodrich and Porter to extract the shear rate-viscosity dependence from batch mixer data. The technique was tested on seven different amorphous and semicrystalline polymers and the results were found to be in reasonable agreement with the data obtained independently with cone-and-plate and capillary rheometers. Contributions of both shear stress between the two cylinders and the stress generated at the wall were evaluated. The latter was found predominant.
Straight asphalt binders have been modified by addition of both high‐density polyethylene (HDPE) and a blend of HDPE and ethylene‐propylene‐diene‐monomer (EPDM). The blend composition was fixed to 90/10 HDPE/EPDM to illustrate the possibility of adapting the polymer to be added to the asphalt binder for specific end‐use applications. Linear viscoelastic properties of unmodified and polymer modified asphalts at concentrations ranging from 1 to 5 wt% were studied before and after Thin‐Film Oven Test (TFOT) aging. Temperatures ranging from −15°C to 60°C were considered. Standard tests such as Ring‐and‐Ball softening point, Fraass breaking point and TFOT aging were also performed on the whole set of samples. It was found that addition of rubber‐modified polyethylene (HDPE/EPDM) to the straight asphalt results in materials with enhanced overall properties, and most important, dispersed phase much more stable than the equivalent HDPE modified asphalt, mainly before TFOT aging. Good results were obtained for 1% HDPE/EPDM samples. Optimum design is, however, required for the desired properties to be obtained.
A procedure based on a Couette analogy, to quantitatively analyze torque/rotor speed data in order to extract viscosity/shear-rate curves using non-conventional geometries is presented. It is first validated using a relatively simple geometry for which the equivalent internal radius used in the analogy can be analytically obtained. The results showed that the equivalent internal radius depends only slightly on the nature of the fluid and that there is an optimal radial position r* in the analog Couette gap where the calculations can be easily performed for computing the viscosity/shearrate data from torque/rotational speed data. The experimental results with complex geometries and complex fluids are found to coincide, within experimental errors, with those obtained using standard geometries over a wide range of shear rates. The approach is also found to be very useful to evaluate shear-rate and viscosity data in Couette viscometers when large gaps are used with non-Newtonian fluids.Nous présentons une procédure basée sur une analogie Couette, permettant d'analyser de façon quantitative des données couple-vitesse angulaire de rotor afin d'extraire des rhéogrammes dans des géométries non conventionnelles. Cette procédure est tout d'abord validée à l'aide d'une géométrie simple pour laquelle un calcul analytique du rayon interne équivalent est possible. Les résultats montrent que ce dernier dépend peu de la nature du fluide et qu'il existe une position radiale optimale, r*, dans l'entrefer Couette virtuel permettant de calculer simplement les valeurs de viscosité-vitesse de cisaillement à partir des données de couple-vitesse angulaire de rotor. Les résultats expérimentaux obtenus à l'aide de géométries complexes et des fluides non-newtoniens complexes coïncident, aux erreurs expérimentales près, avec ceux obtenus à l'aide de géométries conventionnelles, sur une large place de vitesses de cisaillement. Cette procédure s'est avérée particulièrement utile pour des viscosimètres de Couette à entrefer large. Rheological characterization of complex fluids may in certain circumstances be a challenging task when conventional rheometers are used. Some food materials, for example, have microstructures with characteristic dimensions in the order of magnitude of the gap available for flow in the conventional rheometers. Placing a sample of such fluid in these geometries may result in a partial destruction of the internal structure. In other situations, phase separation of the basic constituents of the fluid to characterize occurs while the measurement is in progress. Mixer-type rheometry, consisting of a mixing device with a more or less complex geometry rotating in a fluid contained in a cylindrical tank, provides an alternative solution to such rheological characterization problems (Choplin and Marchal, 1996). Mixing devices with large local spacing can indeed be used to handle fluids with relatively large heterogeneities while providing continuous mixing. Monitoring torque and rotational speed during the mixing process can ...
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