Immiscible blend miscibility

Blends are physical mixtures of polymers. Depending on the extent and type of blend the properties may be characteristic of each blend member or may be some blend of properties. Immiscible blends are phase-separated with the phases sometimes chemically connected. They are generally composed of a continuous and discontinuous phase. HIPS is an example of an immiscible blend. Miscible blends occur when the two blended materials are compatible. Often the properties are a mixture of the two blended materials. The plastic automotive panels and bumpers are generally made from a miscible blend of PE and a copolymer of PE and PP. 

Polymer blends can be divided into two groups miscible and immiscible blends. Miscible blends are homogeneous and stable. Their properties tend to be intermediate. However, they are relatively few. Most polymer blends are immiscible. Their properties are strongly affected by their phase morphologies, which are decided by their viscosity, interfacial tension, and processing methods. In this review we will describe polyolefin blends. Many of these blends involve polar polymers with polyolefins. 

Sulfonation has been used to change some characteristics of blends. Poly(2,6-diphenyl-l,4-phenylene oxide) and polystyrene are immiscible. However, when the polymers were functionalized by sulfonation, even though they remained immiscible when blended, the functionalization increased interfacial interactions and resulted in improved properties (65). In the case of DMPPO and poly(ethyl acrylate) the originally immiscible blends showed increased miscibility with sulfonation (66). 

Tables 5 and 6 summarize key properties and appHcations for miscible and immiscible blends which are either commercial as of 1996 or were commercialized in the past (2,314—316,342,343). Most of the Hsted blends contain only two primary components, although many are compatibiLized and impact-modified. Consequently, an immiscible system consisting of two primary components or phases may contain impact modifiers for each phase and a compatihilizer copolymer, for a total of five or more components.

Though both miscible and immiscible blends are composite materials, their properties are very different. A miscible blend will exhibit a single glass transition temperature that is intermediate between those of the individual polymers. In addition, the physical properties of the blends will also exhibit this intermediate behavior. Immiscible blends, on the other hand, still contain discrete phases of both polymers. This means that they have two glass transition temperatures and that each represents one of the two components of the blend. (A caveat must be added here in that two materials that are immiscible with very small domain sizes will also show a single, intermediate value for Tg.) In addition, the physical properties... 

In this chapter we have discussed the thermodynamic formation of blends and their behavior. Both miscible and immiscible blends can be created to provide a balance of physical properties based on the individual polymers. The appropriate choice of the blend components can create polymeric materials with excellent properties. On the down side, their manufacture can be rather tricky due to rheological and thermodynamic considerations. In addition, they can experience issues with stability after manufacture due to phase segregation and phase growth. Despite these complications, they offer polymer engineers and material scientists a broad array of materials to meet many demanding application needs. 

Barrier polymers, 3 375-405 applications, 3 405 barrier structures, 3 394-399 carbon dioxide transport, 3 403 flavor and aroma transport, 3 403-405 health and safety factors, 3 405 immiscible blends, 3 396-398 large molecule permeation, 3 388-390 layered structures, 3 394-396 miscible blends, 3 398-399 oxygen transport, 3 402 permanent gas permeation, 3 380-383 permeability prediction, 3 399-401 permeation process, 3 376-380 physical factors affecting permeability, 3 390-393... 

The effect of blend miscibility on transport properhes of SPEKK/PEI has been examined by Gasa, Weiss, and Shaw. Miscibilify in fhe SPEKK/PEI system was found to be highly dependent upon the lEC of SPEKK. Thus, miscible blends were found for SPEKK af low ionic confenf (lEC = 0.8 meq/g), whereas the blends were only parhally miscible at lEC = 1.1 meq/g and immiscible at lEC = 1.4 meq/g. In contrast, a blend composed of SPEKK wifh fhe non-ionic PES was miscible across a wide range of lEC values (0.8-2.2 meq/g). Conductivity of the high lEC SPEKK/PEI sample (lEC = 2.2 meq/g) was found to vary as a function of SPEKK content, as shown in Eigure 3.36. 

The effect of blending LDPE with EVA or a styrene-isoprene block copolymer was investigated (178). The properties (thermal expansion coefficient. Young s modulus, thermal conductivity) of the foamed blends usually lie between the limits of the foamed constituents, although the relationship between property and blend content is not always linear. The reasons must he in the microstructure most polymer pairs are immiscible, but some such as PS/polyphenylene oxide (PPO) are miscible. Eor the immiscible blends, the majority phase tends to be continuous, but the form of the minor phase can vary. Blends of EVA and metallocene catalysed ethylene-octene copolymer have different morphologies depending on the EVA content (5). With 25% EVA, the EVA phase appears as fine spherical inclusions in the LDPE matrix. The results of these experiments on polymer films will apply to foams made from the same polymers. 

Miscible blends are not as easy to achieve as immiscible blends. As noted above, entropy is the major driving force in causing materials to mix. Because polymer chains are already in a state of relatively high order, increases in randomness are not easily achieved so that immiscible blends are often more easily formed. To make matters worse, for amorphous polymers the amount of disorder in the unmixed polymer is often higher than for blends that tend to arrange the polymer chains in a more ordered fashion. 

Recently, a new concept in the preparation of TPVs has been introduced, based on the reaction-induced phase separation (RIPS) of miscible blends of a semicrystalline thermoplastic in combination with an elastomer, with the potential for obtaining submicrometer rubber dispersions. This RIPS can be applied to a variety of miscible blends, in which the elastomer precursor phase was selectively crosslinked to induce phase separation. Plausible schematic representation of the morphological evolution of dynamic vulcanization of immiscible and miscible blends is shown in Fig. 9. For immiscible blends, dynamic vulcanization leads to a decrease in the size... 

Fig. 9 Plausible representation of morphology evolution of reactive blending of immiscible and miscible blends...

Selective blending the more viscous PPE phase with PS allowed one to tailor the processing window of the miscible PPE/PS blend phase and the microstructure of the immiscible blend system. Following this approach, simultaneous foaming of both blend phases and more homogeneous cell structures could be achieved. Additionally, the overall foam density could be reduced. 

In this example of model reactive polymer processing of two immiscible blend components, as with Example 11.1, we have three characteristic process times tD,, and the time to increase the interfacial area, all affecting the RME results. This example of stacked miscible layers is appealing because of the simple and direct connection between the interfacial layer and the stress required to stretch the multilayer sample. In Example 11.1 the initially segregated samples do create with time at 270°C an interfacial layer around each PET particulate, but the torsional dynamic steady deformation torques can not be simply related to the thickness of the interfacial layer, <5/. However, the initially segregated morphology of the powder samples of Example 11.1 are more representative of real particulate blend reaction systems. 

Time-temperature superposition works for homopolymers and miscible blends but not for immiscible blends, filled systems (e. g., glass fiber reinforced plastics) or reactive or unstable polymers. 

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