Heterogeneous blend

Polymers can exist in a number of states. They may be amorphous resins, rubbers or fluids or they can be crystalline structures. TTie molecular and the crystal structures can be monoaxially or biaxially oriented. Heterogeneous blends of polymers in different states of aggregation enable materials to be produced with combinations of properties not shown by single polymers. 

Whether or not polymers in different states of aggregation have been heterogeneously blended. 

Unlike incompatible heterogeneous blends of elastomer-elastomer, elastomer-plastic, and plastic-plastic, the reactively processed heterogeneous blends are expected to develop a variable extent of chemical interaction. For this reason the material properties, interfacial properties, and phase morphology of reactively processed blends would differ significantly from heterogeneous mixtures. 

But there is another method — the use of heterogeneous blends of polymers [45, 46], To this end, electrical properties and distribution of the filler (carbon black) in the mixtures of polyethylene and thermodynamically incompatible polymers were investigated. 

One more fact, important in practice, lies in that a of the compositions based on heterogeneous blends of polymers obtained by the method 3, depends considerably on mixing temperature Tm. This is bound up with a variation of the polymer viscosity with the temperature on being introduced into the polymer mixture, a filler becomes distributed mostly in the less viscous polymer and, if the viscosity of polymers is almost the same, it is distributed comparatively uniformly and a of the composition decreases. Therefore, the dependence of a of the conducting polymer composite on Tm has a minimum (by a factor of 102 to 104) in the Tm region when the viscosities of the polymer components are close. 

Thus, the use of heterogeneous blends of polymers is a successful example of creating the ordered structure of the filler distribution conductance occurs when the filler concentration exceeds the threshold cpf in the polymer phase the concentration... 

The existence, on a qualitative basis, of the above-mentioned region (homogeneous diblocks and heterogeneous blends) adds measurably to the understanding of much of our earlier data on rubbery/ rubbery systems. We have recently extended this explanation to a more quantitative level by calculating (7 ) values of Mcri t for various AB pairs. The AB interaction parameter for each pair, re-... 

Here the solid curve representing the boundary between homogeneous and heterogeneous blends is located at a position halfway between the two curves of Figure 1. The various data points shown... 

Glass transition temperature (2 peaks, as is expected for a heterogeneous blend)... 

At the recent European Symposium on Polymer Blends [59] about half of the contributions dealt with thermodynamic effects on molecular architecture, on polymer morphology, and on processing and performance of polymer blend materials. Although some attention has been focused mainly on the interface (material) in heterogeneous blends, in general most thermodynamic studies of such heterogeneous blends deal with two- or more bulk phases. Essential morphological features such as droplet size, cocontinuous phases, micellar or... 

A plastic foam is a heterogeneous blend of a polymer with a gas. The gas cells are between 1 mm and 0.1 mm. Foams are made from thermoplasts, thermosets and rubbers. In all these cases the foam structure is generated in the fluid condition with thermoplasts it is fixed by solidification, with thermosets and rubbers by the curing or vulcanisation reaction. 

Avgeropoulos GN et al. (1976) Heterogeneous blends of polymers. Rheology and morphology. Rubber Chem Technol 49 94... 

Heterogeneous blends with very line scales of segregation may have very broad glass transition regions and good optical clarity. It is a moot point, then, whether such mixtures are compatible. If the components are not truly miscible, the blend is not at equilibrium but the user may not be able to distinguish between a persistent metastable state and true miscibility. 

Fig. 27. Dependence of craze flow stress on weight fraction of low molecular weight PB rubber. The upper branch is for homogeneous blends, the lower for heterogeneous blends ->-2...

Han (28-34) has found that the tenqperature Independence of G when plotted against G" to be a universal feature of all homogeneous visco-elastic fluids. This author has also postulated the general rule that, for a miscible blend, the G -G" plot is invariant to changes in blend concentration, while for heterogeneous blends such Invariance is not observed. However, Roland (35) has shown an exanqple of a miscible blend exhibiting a variation in the G -G" plot as a function of composition, which is at variance with the above-mentioned proposal. 

REDOR was also applied to examine the structure and dynamics of interfaces of heterogeneous polymer blends. A heterogeneous blend was prepared from [carbonyl- C]polycarbonate and poly(p-fluorostyren-co-styrene) copolymer of p-fluorostylene. The blend was formed by coprecipitation from chloroform into methanol. A fluorine dephased REDOR signal indicates that the 1 polycarbonate chain in 20 exists at the interface, suggesting that the polycarbonate phase is embedded in a continuous polystyrene matrix which is 200 A thick or 400 A in diameter [54],... 

Characterization of the interfacial regions is important to understand the mechanical properties of incompatible polymer blends. As shown, in many heterogeneous blends, the simplifying assumption of the neglect of spin diffusion between domains is reconcilable with NMR observations. In other words, most of the NMR observables are not sensitive enough to appreciate the influences of the other domains. However, it is also true that the spins are interacting with each other via the interface. To study such interactions. 

Fig. 10.26. Carbon-observe, fluorine-dephase REDOR NMR spectra of a heterogeneous blend of [carbonyl- CJpolycarbonate and poly(p-fluorostyrene-co-styrene) as a function of the number of rotor cycles of 5 kHz magic-angle spinning. The natural-abundance background has been subtracted from both the top and bottom sets of spectra. The REDOR difference (top) arises exclusively from the polycarbonate carbons at the interface. (Reprinted with permission from Ref. [153]. 1995 American Chemical Society, Washington, DC.)...

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