Single-Phase Blending

The main aim of measurements of the single-phase mixing behavior in a stirred tank is to obtain a mixing time for the system under investigation. The mixing 

In an in-line mixing system, one is usually interested in quantifying how well mixed the fluids are at a particular location, or in a manner similar to the batch mixing time, how many mixer elements are required to achieve a given degree 

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Since this critical interaction parameter is very small for blends of long chains, most polymer blends have x > Xc and thus are phase separated over some composition range (within the miscibility gap). Only blends with either very weak repulsion (0 < x < Xc), or a net attraction between components of the mixture (x < 0) form homogeneous (single-phase) blends over the whole composition range. 

This means that the Flory interaction parameter y can be determined from the low wavevector limit of the scattering function of a single-phase blend of A chains (with monomers) and B chains (with monomers), where o is the volume fraction of A chains. In practice, the concentration fluctuations in the blend provide sufficient scattering contrast for neutron scattering, as long as one of the components is at least partially labelled with deuterium. 

As discussed in Chapter 2 of this Handbook, there is a significant difference in the rate of phase separation and the generated morphology when a single-phase blend is quenched into either the... 

While miscible blends have attracted considerable interest due to the thermodynamic implications and commercial relevance, phase separated blends have had a prominent role in polymer blend technology. While mechanical compatibility is assured in miscible blends, phase separated blends can often achieve property advantages not capable with single phase blends. (Mechanical... 

Thermodynamic compatibility of the components of a polymer material implies their capability for mutual dissolution under certain conditions with the formation of a stable single-phase blend [30]. This state of the material is stable in time, during which no matter or energy is transferred through it [38]. 

The state of thermodynamic equilibrium (implying the formation of a single-phase blend of components) can rarely be reached due to the high viscosity of polymer composite systems. Polymer CM are most often dispersed systems whose composition varies with time and individual components may form phase areas of different sizes. One of their components (the polymer phase) is a continuous dispersed medium, i.e. a matrix, in which all other components are spread as a dispersion of spatially separated particles called a dispersed phase [31],... 

The compatibility of two elastomers can generally be predicted from solubility parameter differences (Table 35-4). If the solubility parameter differences exceed about 0.7, then, two glass transition temperatures are observed and the mixture consists of two phases. Single-phase blends with only one glass transition temperature only occur when the solubility parameters do not differ by more than 0.7. 

Most polymer pairs are too dissimilar for complete miscibility. They reject each other and separate into two or more phases. Generally, the major polymer forms a continuous matrix phase and retains most of its original properties. The minor polymer separates into dispersed domains and may affect certain specific properties. When the domains are extremely fine, sensitive properties may detect the phase separation, but many practical properties may resemble homogeneous single-phase blends. When the domains are larger in size, they will have distinct effects on certain specific properties when these effects are beneficial, the blend is described as theoretically immiscible but practically compatible. When the domains are too coarse, most properties will suffer, and the blend is described as incompatible. 

One of the most basic questions regarding blends is whether the two polymers are miscible or exist as a single phase. In many circumstances, the polymers will exist as two separate phases. In this case the morphology of the phases is of great importance. In the case of a miscible single-phase blend, there is a single Tg, which is dependent on the composition of the blend. When two phases exist, the blend will exhibit two separate Tg values, one for each of the phases present. In the case where the polymers can crystallize, the crystalline portions will exhibit a melting point even in the case where the two polymers are a miscible blend. Miscible blends of commercial importance include PPO-PS, PVC-nitrile rubber, and PET-PBT. 

The detailed nature of single-phase blend correlations, effective interaction parameters, and the entropy-driven phase separation phenomenon have been found to be sensitive to system-specific factors such as composition, differences in A and B site diameter, density, and local architectural details.However, the basic conclusions summarized above seem qualitatively general. 

The very high Tg, high melt viscosity, and a pronounced tendency for PPE to oxidize at processing temperatures made it very difficult to process. However, in 1965 Westlake Plastics Co. started production of extruded rods, sheets, and tubing of PPE under fee Alphalux trademark. Also in 1965 Richardson Co. marketed a miscible blend of PPE with crystal polystyrene, PS. In spite of the PPE/PS miscibility, fee single-phase blend was not a commercial success [21],... 

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