Blends miscible and immiscible

There are two main categories of polymer blends, miscible and immiscible (Figure 3.9). Miscible blends are homogeneous down to the molecular level [33]. Properties scale with the ratios of the coirstituent pol3uners [36]. 

Commercial polymer products are frequently derived from blending two or more polymers to achieve a favorable balance of physical properties. As described in Chap. 2, Thermodynamics of Polymer Blends in this handbook, from the thermodynamic point of view, there are two basic types of polymer blends miscible and immiscible. The vast majority of polymer pairs are immiscible. There are only a few commercially important polymer blends based on miscible or partially miscible (i.e., miscible within a low range of concentration) polymer pairs. It is seldom possible to mix two or more polymers and create a blend with useful properties. Instead, when preparing a new polymer blend from immiscible resins, it is necessary to devise a specific strategy for compatibilizing the mixture to provide for optimum physical performance and long-term stability. Although there do exist a very small number of commercial blends of immiscible polymers that are not compatibilized, most commercially available blends of immiscible polymers have been compatibilized by some specific mechanism. 

There are two types of polymer blends miscible and immiscible. 

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.

We can classify blends into three categories miscible, partially miscible, and immiscible. Miscibility can be defined in thermodynamic terms. For a binary blend to be miscible the following two conditions should be satisfied ... 

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. 

Ruckdaschel H, Rausch J, Sandler JKW, Altstadt V, Schmalz H, Muller AHE (2007) Foaming of miscible and immiscible polymer blends. Mater Res Soc Symp Proc 977... 

PAL has been used to study both miscible and immiscible polymer blends [41, 61, 67-70], PAL results have shown both positive and negative deviations from additivity of free volume with blend composition. In the case of multi phase systems, PAL data analysis is complicated by the fact that Ps may diffuse between the different blend phases. 

The understanding of the formation of miscible and immiscible polymer blends requires the application of the principles of phase chemistry. A miscible blend may be regarded as a solution of one polymer in the other. The thermodynamic criteria for the miscibility of liquids are well known and may be applied to polymers as a first approximation. The added complexity comes from the long-chain nature of polymers. In addition to the entropic factors there are kinetic factors to be considered. Since in reactive processing the reactions are occurring within a short time, they will very often be a long way from equilibrium. 

For partially miscible and immiscible blends, various domain/phase structures can be invoked. Unfortunately, the resonance position of a particular spin in each domain is not appreciably affected by its respective domain structure (see Section 10.2.2.1). Therefore, we cannot expect to observe highly resolved NMR resonances for different domains. Since relaxation times are different for each domain, a relaxation curve is observed to be a featureless multiexponential one and, in most of the cases, is too monotonous to include interdomain spin diffusion. Therefore, most of the experimental results have been explained by using the simplified picture of no interdomain spin diffusion and the observed multiexponential decay is fitted to a sum of exponential functions. Practically three exponentials are enough to realize the observed decay. Each relaxation time represents one domain, thus, only a few domains can be distinguished by one resonance line. Inevitably, the heterogeneous structures deduced from NMR relaxation experiments become simple. 

The crystallization of miscible and immiscible polymer blends can differ remarkably from that of the neat crystallizable component(s). In the case of crystallizable miscible blends (discussed in this section), important polymer characteristics with respect to crystallization are the chemical nature and molecular mass of the components, their concentration in the blend, and the intermolecular interactions between the components. 

Table 7.1. Rheological models for miscible and immiscible blends...

Chuang and Han [1984] reported that for miscible and immiscible blends at constant composition, the plots of Nj vs. 0 2 and G vs. G are independent of T. However, while for single phase systems the two dependencies are approximately parallel, for immiscible blends, such as PS/PMMA, the steady state relation may be quite different from the dynamic one. 

In terms of miscibility, polyolefin blends may also be classified as miscible and immiscible blends (10, 11). Polyolefin blending requires knowledge of the miscibility and crystallinity of the blend, in addition to the contributions of the components of the blend. Miscibility depends on molecular structure, blend composition, and mixing temperature. To characterize miscibility, a phase diagram is needed. 

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. 

These blends are immiscible and their interfaces are unstable. Special interfacial treatments are required to make them suitable as materials of commerce. A second group of blends are those in which the components are all polyolefins. These blends will be miscible or nearly so. Also in this paper the general questions of blend miscibility and interfacial characteristics will be treated. 

We begin in Section 9.2 with the morphology in binary blends of iPP and various rubbery olefin copolymers where we remark the interrelation between the miscibility and dynamic mechanical properties. Section 9.3 describes the molecular orientation behavior under tensile deformation of iPP-based blends, and we compare the differences in deformation behavior between miscible and immiscible blends. Section 9.4 contains the solidification process in iPP-based blends where the effects of miscibility in the molten state on the crystallization of iPP matrix are discussed. 

Takahashi, T., J.-I. Takimoto, and K. Koyama. 1999. Elongational viscosity for miscible and immiscible polymer blends, n. Blends with a small amoimt of UHMW polymer. Journal of Applied Polymer Science 72 961-969. 

Equation-5, X and Phi denote the molar and volume fiaetion of the components, respectively. Eor two polymers to be miscible, the free energy of mixing must be negative. If the solubility parameters of the polymer pairs are too far apart, the free energy of mixing becomes positive, and compatibilizers are often needed to reduce the interfacial tension between incompatible components in a blend. In industry, both miscible and immiscible polyblends are important materials because they fill (filFerent market needs. 

The frequent interruption in the crystallization of a semicrystalline/amorphous blend with the incorporation of salt not only elevates its T, but also reduces the crystallization kinetics and G of the crystallizable component in both miscible and immiscible blends (Rocco et al., 2002 Rocco et al., 2004 Chan and Rammer, 2008 Florjanczyk et al., 2004 Acosta and Morales, 1996). Salt-free miscible PEO/PBE 60/40 blend exhibits an exothermic crystallization peak at -31 °C, but... 

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