Immiscible blended polymer

Karasz and McKnight (1977) have developed a model based on segmental interaction parameters in copolymers to quantify these qualitative interactions. Each segment in a copolymer conriibutes to both a configurational and an enthalpic term due to chemical interaction. A pair of copolymers can be miscible or immiscible, or a single polymer can act as a compatibilizer, or an immiscible blend polymer can act as a compatibilizer. Paul and Barlow have shown that A H may be negative in a blend due to dilution of more unfavorable interactions, where at least one component in the blend is a copolymer (Paul and Barlow, 1980). 

Miscible polymer blend polymer blend, homogenous down to the molecular level, in which the domain size is comparable to the macromolecular dimension associated with negative value of the free energy of mixing, AG Aff , < 0, and within the phase stability condition cP hGmld > 0 Immiscible blends polymer blends whose free energy increases upon mixing, i.e., AG , ci... 

Gleisner, W., Braun, H., Friedrich, Chr., and Cantow, H.-J. (1994) Correlation between rheology and morphology of compatibilized immiscible blends. Polymer, 35 (2), 128-135. 

For the immiscible blended polymer type, phase-separated mixtures are obtained when one tries to mix most polymers. However, strangely enough, the phase-separated materials also turn out to be sometimes useful. The examples of immiscible polymer are polystyrene and polybutadiene. When polystyrene is mixed with a small amount of polybutadiene, the two polymers do not blend. Polybutadiene separates from the polystyrene into Uttle spherical blobs. 

Li M F, Xiao R and Sun G (2011) Formation and morphology development of poly(butylene terephthalate) nanofibers from poly(butylene terephthalate)/cellulose acetate butyrate immiscible blends, Polym Eng Sci 51 835-842. 

R. Ratnagiri and C. E. Scott, Effect of Viscosity Variation with Temperature on the Compounding Behavior of Immiscible Blends, Polym. Eng. Sci. 39(9), 1823-1835 (1999). 

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). 

Fig. 6. Illustration of (a) compatibiLization of immiscible blends of polymers and B by block or graft copolymers and (b) the subsequent modification of...

Immiscible Blends. When two polymers are blended, the most common result is a two-phase composite. The most interesting blends have good adhesion between the phases, either naturally or with the help of an additive. The barrier properties of an immiscible blend depend on the permeabihties of the polymers, the volume fraction of each, phase continuity, and the aspect ratio of the discontinuous phase. Phase continuity refers to which phase is continuous in the composite. Continuous for barrier appHcations means that a phase connects the two surfaces of the composite. Typically, only one of the two polymer phases is continuous, with the other polymer phase existing as islands. It is possible to have both polymers be continuous. 

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... 

Esseghir, M., Gogos, C. G., Yu, D., Todd, D. B., and David, B., A Comparative Study on the Performance of Three Single-Screw Elements in Melt-Melt Mixing of Immiscible Blends, Adv. Polym. TechnoL, 17, 1 (1998)... 

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. 

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. 

Thus most of the time one obtains phase-separated systems in which the macromolecules of component A are not at all or only to a limited extent miscible with the macromolecules of component B, i.e., polymer A is incompatible or only partially compatible with polymer B. The synonymical terms polymer blend , polymer alloy , or polymer mixture denote miscible (homogeneous) as well as immiscible (heterogeneous) systems consisting of two or more different polymers. 

Other models are based upon the immiscibility of polymer blends described above, and they model the system as Newtonian drops of the dispersed polymer with concentration (pi in a Newtonian medium of the second polymer with concentration (p2 = — (pi. There exists some concentration, cpu = cp2i — 1, at which phase inversion takes place that is, at snfficiently high concentration, the droplet phase suddenly becomes continuous, and the second phase forms droplets. The phase inversion concentration has been shown to correlate with the viscosity ratio, A. = r i/r 2, and the intrinsic viscosity for at least a dozen polymer alloys and blends ... 

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