Distributive and Dispersive Mixing

In dispersive mixing, the dispersed phase undergoes size reduction and forms multiple smaller domains as a result of stresses acting at the interfaces [53, 54]. In this case, the viscous forces generated in the continuous phase overcome the restoring forces due to interfacial tension [55, 56]. Hence, the extent of deformation is determined by the ratio of the viscous and interfadal stresses, the relative magnitude of which can be expressed as a dimensionless number, the so-called capillary number [57, 58]. 

In distributive mixing, the flow field produces deformation in the dispersed phase, without inducing breakup. As a consequence, a lamellar morphology of alternating striations of dispersed phase and the matrix is obtained, which can be characterized by the striation thickness distribution. Note that the striation thickness (5) is a function of the initial length scale (la), viscosity of the dispersed phase r]i), total shear strain (y) (product of shear rate and time), volume fraction of the dispersed phase (4 a), and viscosity of the matrix (rim) [59] (Eq. (3.1))  

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K. Allemaskin, I. Manas-Zloczower, and M. Kaufman, Simultaneous Characterization of Dispersive and Distributive Mixing in a SSE, Conference Proc., SPEANTEC, 61,268-272 (2003). 

Alemanskin et al. (79) extended the use of the entropic measure of mixing to both dispersive and distributive mixing using essentially modified Shannon entropy for systems with multiple species. These authors have also employed entropy to asses color homogeneity in extruded samples by means of computer image analysis and using standard direct red-blue-red (RGB) correlations (80,81). 

More efficient dispersive and distributive mixing thanks to higher intermeshing zone volume. 

Kneaders are effective mixers for making color concentrates because they are excellent for both dispersive and distributive mixing. The main attribute of a kneader is uniform control of heat and dwell since there is no localized high-shear zone to overmix or overheat sensitive polymer like polyvinyl chloride (PVC). 

From the economic as well as the performance points of view, the reactive compatibUization is most interesting (see Chapter 5). The process involves (i) sufficient dispersive and distributive mixing to ascertain required renewal of the interface, (ii) presence of a reactive functionality, suitable to react across the interphase, (iii) sufficient reaction rate making it possible to produce sufficient quantity of the compatibiUzing copolymer within the residence time of the processing unit The method leads to particularly thick interphase, thus good stability of morphology. 

These factors affect both the dispersive and distributive mixings. 

Narrow residence time distribution High dispersive and distributive mixing Very high feeding efficiency Low pumping efficiency Reduced degassing efficiency... 

Single-screw compounding is intrinsically very limited in both dispersive and distributive mixing. 

Reactive compatibilization requires good dispersive and distributive mixing of reactants and sufficient residence time for the reaction to take place. The introduced components should be immediately uniformly mixed. Thus, appropriate mixing screw elements (kneading, turbine, etc.) should be placed in the reaction zone of the... 

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