Mixing, dispersive

Dispersive mixing is the process of reducing the size of a component within a polymer melt (Fig. 2.22). Consider the addition of color pigment or calcium carbonate to a polymer matrix. These additives are in particulate form and need to be reduced in size (broken up) before they can be adequately distributed throughout the matrix. Dispersive mixing breaks them up. 

The most common example of dispersive mixing of particulate solid agglomerates is the dispersion and mixing of carbon black into a rubber compound. The dispersion of such a system is schematically represented in Fig. 3.22. However, the break up of particulate agglomerates is best explained using an ideal system of two small spherical particles that need to be separated and dispersed during a mixing process. 

If the mixing device generates a simple shear flow, as shown in Fig. 3.23, the maximum separation forces that act on the particles as they travel on their streamline occur when they are oriented in a 45° position as they continuously rotate during flow. However, if the flow field generated by the mixing device is a pure elongational flow, such as shown in Fig. 3.24, the particles will always be oriented at 0° the position of maximum force. 

In general, droplets inside an incompatible matrix tend to stay or become spherical due to the natural tendencies of the drop to maintain the lowest possible surface-to-volume ratio. 

Force applied to a two particle agglomerate in a simple shear flow. 

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Clarke,. 1. and Freakley, P.K., 1995. Modes of dispersive mixing and filler agglomerate size distributions in rubber compounds, Plast. Rubber Compos. Process. Appl. 24, 261-266. 

Motionless mixers continuously interchange fluid elements between the walls and the center of the conduit, thereby providing enhanced heat transfer and relatively uniform residence times. Distributive mixing is usually excellent however, dispersive mixing may be poor, especially when viscosity ratios are high,... 

The table data show that the stress/strain properties of compositions are improved by additional dispersion (mixing). Ultrasonic analysis is sufficiently reliable and informative as a means of mixing quality assessment. The very small change of the characteristics for filled compositions (chalk + kaolin) can be due to the fact that these fillers are readily distributed in the matrix as they are. 

We prepared ceria on Ni substrate by sol-gel coating method. Ceria sol solution was prepared with ceria sol solution (Alfa, 20% in H2O, colloidal dispersion) mixed with ethanol (99.9%, Hayman) with weight ratio (1 2) and stirred. Ceria was deposited on Ni substrate by dip coating method. The variation number of dipping was carried out to obtain different coating ratio. The anode was completely dipped into the ceria sol solution for several seconds and dried at a temperature of 50 C for 24 hours in air atmosphere followed by calcination at 700 C for 30 minutes in 5%H2-N2 atmosphere. 

Manas-Zloczower, I., Dispersive mixing of solid additives, in Mixing and Compounding of Polymers—Theory and Practice. (I. Manas-Zloczower and Z. Tadmor, Ed.) Hanser Publishers, Munich, 1994, pp. 55-83. 

Manas-Zloczower, I., Nir, A., and Tadmor, Z., Dispersive mixing in internal mixers—a theoretical model based on agglomerate rupture. Rubber Chem. Tech 55, 1250-1285 (1982). 

Explain the differences between dispersive and distributive m being. Why does dispersive mixing rely on shearing processes, while distributive mixing relies on iteratively folding the polymer melt back on itself ... 

For any given size of mill there is a minimum volume of polymer per unit width of roll, below which no dispersive mixing occurs. Increasing the amount of material above this minimum level increases the high shear zone in the polymer, increasing dispersive mixing. There is an upper limit however, above which a circulatory flow develops at the entrance to the nip region and no further improvement occurs. 

Flush models can also be configured to simulate the effects of dispersive mixing. Dispersion is the physical process by which groundwaters mix in the subsurface (Freeze and Cherry, 1979). With mixing, the groundwaters react with each other... 

Fig. 2.9. Use of a flush model to simulate dispersive mixing. Two fluids enter a unit volume of an aquifer where they react with each other and minerals in the aquifer, displacing the mixed and reacted fluid.

Fig. 21.4. Transport of benzene within an aerobic aquifer, modeled in two dimensions. Contaminated water containing 1 mg kg-1 benzene leaks into the aquifer over the course of two years, at the point indicated. As in the previous model (Fig. 21.3), the benzene is retarded by sorption to organic matter in the aquifer and attenuates due to sorption, biodegradation, and dispersive mixing. Plots were rendered using the matlab software.

AV reciprocating tachycardia, 5 108 Axial dispersion coefficient, 10 762 Axial dispersion/mixing, 10 762-763 in adsorption columns, 2 604 in bubble tray absorbers, 2 88-89 chromatographic adsorption, 2 610 in packed column absorbers, 2 61-65 Axial dissolved oxygen profiles, 25 707-708 Axial filtration, 22 385-386 Axial-flow angular-momentum flowmeter, 22 672-673... 

Elemans, P.H.M. and van Wunnik, J.M., The Effect of Feeding Mode on Dispersive Mixing Efficiency in Single-Screw Extrusion, Polym. Eng. Set, 41, 1099 (2001)... 

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