Blending miscible components

The two generic terms found in the blend literature are compatibility and miscibility. Components that resist gross phase segregation and/or give desirable blend properties are frequently said to have a degree of compatibility even though in a thermodynamic sense they are not miscible. In the case of immiscible systems, the overall physicomechanical behavior depends critically... 

Diblock copolymers, especially those containing a block chemically identical to one of the blend components, are more effective than triblocks or graft copolymers. Thermodynamic calculations indicate that efficient compat-ibilisation can be achieved with multiblock copolymers [47], potentially for heterogeneous mixed blends. Miscibility of particular segments of the copolymer in one of the phases of the bend is required. Compatibilisers for blends consisting of mixtures of polyolefins are of major interest for recyclates. Random poly(ethylene-co-propylene) is an effective compatibiliser for LDPE-PP, HDPE-PP or LLDPE-PP blends. The impact performance of PE-PP was improved by the addition of very low density PE or elastomeric poly(styrene-block-(ethylene-co-butylene-l)-block styrene) triblock copolymers (SEBS) [52]. 

Because the components must initially form miscible solutions or swollen networks a degree of affinity between the reacting components is needed. Therefore, most of the investigations into epoxy IPNs have involved the use of partially miscible components such as thermoplastic urethanes (TPU) with polystyrenes [57], acrylates [58-61] or esters which form loose hydrogen-bound mixtures during fabrication [62-71 ]. Epoxy has also been modified with polyetherketones [72],polyether sulfones [5] and even polyetherimides [66] to help improve fracture behavior. These systems, due to immiscibility, tend to be polymer blends with distinct macromolecular phase morphologies and not molecularly mixed compounds. 

The composition dependence of Tg of binary (starch-water) or ternary (starch-sugar-water) blends, assuming component miscibility and the absence of crystallinity... 

Miscible Blends. Both Components Amorphous. Certainly one of the most commercially important and publicized examples of a miscible polymer blend system is that based on polystyrene and poly(phenylene oxide), which is sold under the trade name Noryl by General Electric. Many fundamental studies of this system have been published, many of which were devoted to proving that these two components are miscible in a thermodynamic sense (see chapter 5 of Ref. 10 by MacKnight, Karasz, and Fried). Commercial interest in this system involves both... 

For sPS/PPE blends, DSC and DMTA measurements give a single Tg value [16-19], intermediate between those of the components and dependent on composition. The Tg values of sPS and PPE being very different from each other (98 and 220 °C, respectively), this result constitutes an unambiguous proof of blend miscibility within the whole composition range. 

Chen et al. [67,68] further extended the study of binary blends of ESI over the full range of copolymer styrene contents for both amorphous and semicrystalline blend components. The transition from miscible to immiscible blend behavior and the determination of upper critical solution temperature (UCST) for blends could be uniquely evaluated by atomic force microscopy (AFM) techniques via the small but significant modulus differences between the respective ESI used as blend components. The effects of molecular weight and molecular weight distribution on blend miscibility were also described. 

After the examination of the PS photooxidation mechanism, a comparison of the photochemical behavior of PS with that of some of its copolymers and blends is reported in this chapter. The copolymers studied include styrene-stat-acrylo-nitrile (SAN) and acrylonitrile-butadiene-styrene (ABS). The blends studied are AES (acrylonitrile-EPDM-styrene) (EPDM = ethylene-propylene-diene-monomer) and a blend of poly(vinyl methyl ether) (PVME) and PS (PVME-PS). The components of the copolymers are chemically bonded. In the case of the blends, PS and one or more polymers are mixed. The copolymers or the blends can be homogeneous (miscible components) or phase separated. The potential interactions occurring during the photodegradation of the various components may be different if they are chemically bonded or not, homogeneously dispersed or spatially separated. Another important aspect is the nature, the proportions and the behavior towards the photooxidation of the components added to PS. How will a component which is less or more photodegradable than PS influence the degradation of the copolymer or the blend We show in this chapter how the... 

If there are more than two components in a mixture (as in a blend of a homopolymer with a copolymer), binary interaction parameters can be combined into a composite % parameter to describe the overall behavior of the system. For example, Choi and Jo [11] showed how the effects of copolymer sequence distribution in blends of polyethylene oxide) with poly(styrene-co-acrylic acid) can be described by an atomistic simulation approach to estimate the binary intermolecular interaction energies which are combined into a total interaction parameter for the blend. Their paper [11] also provides a list of the many preceding publications attempting to address the effects of copolymer composition, tacticity, and copolymer sequence distribution on polymer blend miscibility. In addition to the advances in computational hardware and software which have made atomistic simulations much faster and hence more accessible, work in recent years has significantly improved the accuracy of the force fields [12] used in such simulations. 

Some polymers have been found miscible with many other resins, or in other words there are many immiscible blends whose components are miscible with the same polymer. Addition of this polymer can be used to partially homogenize the system, i.e., to compatibilize the blend. The added polymer is a co-solvent. Of particular interest are systems in which presence of a co-solvent makes it possible for the two immiscible components to form three-body interactions. In this case, the blend is indeed compatibilized, with the co-solvent being located in the interphase. For the thermodynamic reasons, mostiy copolymers belong to this type of co-solvents. In the left hand side column of Table 4.1 there are polymers that may be used as co-solvents for pairs of resins listed in the other column. Some of the latter resins may show local miscibihty (e.g., PS with styrenic copolymers), but the vast majority is immiscible. 

Crystallization may take place only within the temperature region limited on the upper side by the melting point, T, and on the lower side by the glass transition temperature, T. The crystallization behavior very much depends on the state of miscibility, as well as on the nature of other blend s components. In miscible blends Tg is a monotonic function of the components T s. When the second component is amorphous, its presence can either decrease or increase the tendency of the first resin to crystallize. The process depends on the blending effects on T and on the chain mobility (the free-volume effect). When T of the amorphous component is lower... 

By definition, miscible polymer blends are singlephase mixtures. Miscibility depends on the molecular weight, concentration, temperature, pressure, deformation rate, etc. Flow of these systems can be compared to that of solutions of low molecular weight, miscible components, or to flow of mixtures of polymeric fractions. Both models are far from perfect, but they serve to illustrate the basic behavior of miscible systems. 

On the other hand, if one looks at the whole system, a number of phenomena can take place segregation, encapsulation, interlayer slip or variations of miscibility. Components can segregate during the flow, leading to spatial redistribution, encapsulation of one phase by the other being a special case of flow segregation. A redistribution of the phases was observed for HDPE/PA-6 blends during capillary flow [Dumoulin et al.,... 

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. 

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. 

Chlorinated polymers/Copolyester-aniides Recent studies (5) of blends of chlorinated polyeAylenes with caprolactam(LA)-caprolactone(LO) copolymers have been able to establish a correlation between miscibiUty and chemical structure within the framework of a binary interaction model. In some of the blends, both components have the ability to crystallize. When one or both of the components can crystallize, the situation becomes rather more complicated. Miscible, cystallizable blends may also undergo segregation as a result of the crystallization with the formation of two separate amorphous phases. Accordingly, it is preferable to investigate thermal properties of vitrified blends. Subsequent thermal analysis also produces exothermic crystallization processes that can obscure transitions and interfere with determination of phase behavior. In these instances T-m.d.s.c has the ability to separate the individual processes and establish phase behavior. 

Conclusions T-m.d.s.c. has already become an indispensable tool for polymer blends studies. Its main advantage is in resolving phase behavior in those situations where additional exothermic processes are present. However, as far as miscibility studies of polymer blends involving components with comparable glass transition temperatures is concerned, we still have to rely on the enthalpy recovery method, that is, assuming that thermal analysis is the experimental technique selected. 

Clearly, the T value for component 1 in miscible blends is responsible for much of the crystallization behavior of component 2. This is most clearly illustrated by our recent data for PVF2 in blends with a variety of miscible components whose Tg varied rather widely (12). To illustrate this we return to case (c) in Fig. 4 where we define (w2)q the limiting composition at which crystallinity no longer develops during cyclic DTA. Fig. 6 shows the... 

In partly miscible systems, interactions cause a glass transition shift of the pure components toward each other. For immiscible blends, the components are completely separated in different phases and the glass transitions of the pure components remain at their original temperature. Here it is important to emphasize that the appearance of one glass transition is not a measure of complete misdbiUty rather than a correlation with domain sizes of less than 15 nm. Various examples were discussed elsewhere [95]. 

Excitation fluorescence is the principle of the fluorescence techniques used for studying polymer blends. The method comprises of three steps incorporation of an excimer, its excitation, and recording the excitation delay. The excimer can be an aromatic polymer component of the blend (viz., PS, poly(viny 1-dibenzyl), polyvinylnaphthalene, an aromatic group grafted onto the macromolecular chain, etc.), or it can be added as probe molecule (e.g., anthracene). There are three possibilities for the aromatic rings to form excimers intramolecular adjacent, intramolecular nonadjacent, and intermolecular types. Each of these types is sensitive to different aspects of the chain conformation and environment, thus, sensitive to blend miscibility effects. The most important of these for studies of polymer blends is the intermolecular, usually identified from concentration measurements (Wiruiik et al. 1988). 

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