Types of polymer blends

The simplest method for preparation of polymer blends involves finding a mutual solvent. If the polymer blend is highly immiscible in the solid state, it will often show phase separation in solution with a common solvent with two layers observed (if densities of the solvent-polymer phases are different). If phase separation occurs in solution, the agitated solution will appear turbid or opaque if sufficient refractive index contrast is present. Observation of 

Another procedure for preparing polymer blends involves in-situ polymerization. In many cases, the polymerization of one polymer is conducted in the presence of the other polymer. Impact polystyrene and ABS are typically prepared by polymerization of styrene or styrene-acrylonitrile in the presence of a high molecular weight rubber. Polyolefin blends can be made by the sequential polymerization of compositionally differing polyolefins (e.g., PP/EPR) or by the simultaneous polymerization of polyolefin variants with multiple catalyst systems. 

In the discussion of specific polymer blends, there are examples where the phase behavior (miscibility) reported in the literature present different results. These examples typically include those polymer blends, which exhibit xn values 0 thus borderline miscibility. With borderline miscibility, the experimental protocol can critically affect the observed phase behavior. Many of these cases involve solvent cast films, where the choice of solvents and casting/annealing conditions can affect the phase behavior, as discussed earlier in this section. Not surprisingly, discrepancies exist in the literature concerning these blends and the different observations are noted in the specific discussions to follow. For miscible blends with specific interactions (xn 0), the phase behavior reported in the literature is in much clearer agreement. 

It has been estimated that polymer blends and alloys consume about 30 wt% of all manufactured polymers with about 9 % per annum growth in sales volume. The principal market for all blends is the automotive industry, which accounts for about 60 % of world consumption with about 

3 % yearly growth. Substitution of plastic for metal in cars results in weight savings that improves gas mileage. Other important markets for polymer blends include computer and other business machine housings, electrical components such as connectors, appliances, consumer products, recreational equipment, construction and industrial applications. 

Commercial activity is mirrored by technological activity. It was estimated that roughly 87,000 patents appeared worldwide on all aspects of polymer blends between 1970 and 1987 averaging almost 5,000 patents per year [Juliano, 1988]. The pace appears to have slowed little since then. 

When two immiscible polymers are blended without compatibilization, one generally obtains a mixture with physical properties worse than those of either individual polymer. Usually such a blend has poor structural integrity and poor heat stability since there is no mechanism for stabilizing a dispersion of one polymer in a matrix of the other. On a macroscopic scale the blend may appear heterogeneous and in the extreme case delaminated. 

Quite generally, the goal in any blending of polymers is to obtain one or all of the following benefits higher heat distortion temperature (HDT), improved variable temperature impact resistance, solvent resistance, dimensional tolerance, higher flow, utilization of recycle/regrind, and lower cost. 

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The relationship between glass temperature and composition for different types of polymer blends may be established on the basis of Eq. (110). According to Hirai-Eiring theory20, the partial free-volume is... 

Figure 1. Generalized mechanical loss (tan S) and modulus behavior for different types of polymer blends. Case 1 (dashed-dotted line), miscible case 2 (dashed line), limited miscibility case 3 (dotted line), microheterogeneous case 4 (solid line), heterogeneous. (Reproduced with permission from Ref. 5. Copyright 1979 Academic Press.)...

The importance of the concentration of polymer having a broad secondary loss maximum upon the loss modulus bandwidth of polymer blend materials is shown in Fig. 11 for the bulk polymerized IPN s of Huelck. (i ) The loss modulus temperature bandwidth constant is strongly dependent upon the concentration of methyl methacrylate, irrespective of whether methyl methacrylate is present in the matrix or the inclusions. Overall the Oberst type of analysis indicates that for a given type of polymer blend the area under the E" curve tends to be constant. In other words, one may have height or width but not both. 

Figure 5.1. Schematic illustrations of the general types of polymer blend phase diagrams, for the simplest case of binary blends without the additional complications that are sometimes introduced by competing processes such as the crystallization of one of the components. The coefficients dg and d refer to the general functional form for %Ag given by Equation 5.7 [10].

Since, at the critical point of a certain polymer, this polymer is always eluted at the same retention time (corresponding to = IX fiU different types of polymer blends containing this polymer as one component may be separated. This is demonstrated in Fig. 26 for PMMA- containing blends. Even chemically very similar blend components, such as poly(cyclohexyl methacrylate) (CHMA) and PMMA were separated. In addition, not only blends of homopolymers, but also blends of copolymers and PMMA may be investigated. Like the homopolymers, poly(styrene-co-acrylonitrile) and poly(styrene-co-methyl methacrylate) (CoStMMA) were eluted in the SEC mode. 

The adjoining Fig. 6.11b plots the probability of successful nucleation as a ftmetion of template feature size as compiled from Fig. 6.11a and similar data sets. Several observations can be made from this array of data. First, a minimum template feature size of 50-200 nm is necessary to have a chance of nucleating phase separation, and the probability of successful nucleation is statistical in nature. Second, the probability of successful nucleation and the size of the induced features depend on the polymer blend ratio. While this data set was only acquired for one type of polymer blend film that follows a nucleated phase separation schemed in Fig. 6.6a-e, the size effects and the statistical nature... 

The mixing action that takes place during blending of these three general types of polymer blends and the physical phenomena that dominates each one of them can be broken down into two major categories - distributive mixing and dispersive mixing. 

In addition to the outlined morphological difference between the two types of polymer blends, without and with hydrogen bonding between the blend partners, it turned out that the mechanism of formation of the nano-sized materials is completely different for the one or the other case. Detailed studies on the mechanism of formation of the individual micro- and nanofibrils led to the conclusion that it takes place during the cold drawing via coalescence of the elongated droplets [18], as schematically illustrated in Figure 9.9. 

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. 

This chapter has reviewed applications for polymer blends from the dual perspectives of material development and application requirements. It indicates the viability of various types of polymer blends for current markets and emerging opportunities. 

There are two types of polymer blends miscible and immiscible. 

Basic problems associated with the equilibrium and interfacial behavior of polymers, compatibilization of immiscible components, phase structure development, and the methods of its investigation are described herein. Special attention is paid to mechanical properties of heterogeneous blends and their prediction. Commercially important types of polymer blends as well as the recycling of commingled plastic waste are briefly discussed. 

IPNs A type of polymer blend prepared to modify the properties of NR. They are composed of two or more polymers with at least one being poly-merized/crosslinked in their networks both without and/or with covalent bonds between the chains of the same or different polymer types. They can be categorized into two types non-covalent IPNs and covalent semi-IPNs (Figure 7.1). For the covalent semi-IPNs, the crosslinked covalent bonds occur between the different polymer chains. In addition, non-covalent IPNs can be further categorized into full IPNs and semi-IPNs. Full IPNs are defined as a combination of NR and other polymers in a network in which each is synthesized by polymerization with a crosslinking agent. In semi-IPNs, in contrast, only one type of polymeric component is crosslinked. However, there are no covalent bonds between the chains of the different polymer types, but the chains of the polymer become inserted into the framework of the other polymers. Moreover, pseudo-IPNs are defined as a type of IPN in which one of the... 

Multicomponent polymeric materials consist of polymer blends, composites, or combinations of both. A polymer blend has two definitions The broad definition includes any finely divided combination of two or more polymers. The narrow definition specifies that there be no chemical bonding between the various polymers making up the blend. Table 2.5 and Section 2.7 summarize the basic types of polymer blends based on the broad definition primarily these are the block, graft, star, starblock, and AB-cross-linked copolymers (conterminously grafted copolymers), interpenetrating polymer networks, as well as the narrow definition of polymer blends. More complex arrangements of polymer chains in space can be shown to be combinations of these several topologies. 

While this brief chapter cannot cover all of the types of polymer blends and composites known in the literature (1-3), Rgures 13.1 (4) and 13.2 (5) categorize the more important classes of polymer blends and composites, respectively. Figure 12.30 already summarized the classification of polymer interfaces. 

This chapter has provided a brief presentation of the underlying theories, and the analytical tools and techniques used to characterize polymer blends by X-ray scattering (SAXS and WAXS). The text was not aimed at reviewing the studies conducted with all types of polymer blends - that is, miscible versus immiscible... 

As another example of the special type of polymer blend studied with EM, the SEM images of a biopolymer-based compound are presented in Figure 17.12. Recently, the encapsulation of curcumin in submicrometer spray-dried chitosan/ Tween 20 particles was evaluated using SEM imaging [84]. Tween 20 was a commercially available version of polyethylene glycol sorbitan monolaurate. The encapsulation of curcumin is important, as its optimal delivery in medicinal... 

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