Properties of Miscible Blends

The basic issue confronting the designer of polymer blend systems is how to guarantee good stress transfer between the components of the multicomponent system. Only in this way can the component s physical properties be efficiently used to give blends with the desired properties. One approach is to find blend systems that form miscible amorphous phases. In polyblends of this type, the various components have the thermodynamic potential for being mixed at the molecular level and the interactions between unlike components are quite strong. Since these systems form only one miscible amorphous phase, interphase stress transfer is not an issue and the physical properties of miscible blends approach and frequently exceed those expected for a random copolymer comprised of the same chemical constituents. 

Miscible polymer blends behave similar to what is expected of a single phase system. Their properties are a combination of the properties of the pure components and in many cases they are intermediate between those of the components. The characteristics of the components affecting the properties of miscible blends are their chemical structure and molecular weight, their concentra-... 

CeccomUi G, PizzoU M, Scandola M (1993) Effect of a low-molecular-weight plasticizer on the thermal and viscoelastic properties of miscible blends of bacterial poly(3-hydroxybutyrate) with cellulose acetate butyrate. Macromolecules 26 6722-6726 Chanprateep S, Kikuya K, Shimizu H, Shioya S (2(X)2) Model predictive controller for biodegradable polyhydroxyalkanoate production in fed-batch culture. J Bacterid 95 157-169 Chen GQ, Wu Q (2005) The application of polyhydroxyalkanoates as tissue engineering materials. Biomaterials 26 6565-6578... 

The rheological properties of miscible blends tmder different temperatures can be obtained from some theoretical models. One such model is the double reptation self-concentration. The DRSC (double reptation self-concentration) model actually includes the temperature dependency and concentration dependency through a complex mixing mle given by the double reptation model and self-concentration model, which helps to exclude the complex contribution from miscible components under different temperatures in the experimental data and only illustrate the effect of the concentration fluctuation and interface formation. This model is applied to study PMMA/SMA (Wei 2011). 

The broadening of the dielectric spectra has to be considered as an intrinsic feature of the dielectric properties of miscible blends. Moreover, the broadening of the a-relaxation increases with the difference of the glass transition temperatures. 

These two examples, then represent cases of synergies being observed in the mechanical properties of miscible blends. These effects are likely due to improved packing of the polymer chains, as observed in the case of LCP/LCP blends. 

In theory, properties of miscible blends should be additive (linear behavior) based on the linear contribution from each polymer fraction [16]. Some properties such as glass transition temperatures and heat distortion temperatures exhibit near-linear behavior in PPE/PS blends, as shown in Fig. 9.2 [17, 18]. 

Other Physical Chemical Properties of Miscible Blends.—Other workers have been examining the nature of miscible blends and the phase separation process. 

The chapter is divided into five sections. Section 10.2 deals with the thermodynamics of polymer blends the general principles and the main theories on the phase behavior of polymer mixtures are briefly presented. Section 10.3 deals with the properties of miscible blends with crystallizable components. The phase morphology, crystal growth rate, overall crystallization kinetics, and melting behavior of miscible blends are analyzed. The crystallization phenomena in blends with miscibility gap are also described. Then, examples of miscible systems comprising one or two crystallizable components are reported with particular attention to the thermodynamic and kinetic aspects of the crystallization process. 

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... 

Polyvinyl alcohol (PVA), which is a water soluble polyhidroxy polymer, is one of the widely used synthetic polymers for a variety of medical applications [197] because of easy preparation, excellent chemical resistance, and physical properties. [198] But it has poor stability in water because of its highly hydrophilic character. Therefore, to overcome this problem PVA should be insolubilized by copolymerization [43], grafting [199], crosslinking [200], and blending [201], These processes may lead a decrease in the hydrophilic character of PVA. Because of this reason these processes should be carried out in the presence of hydrophilic polymers. Polyfyinyl pyrrolidone), PVP, is one of the hydrophilic, biocompatible polymer and it is used in many biomedical applications [202] and separation processes to increase the hydrophilic character of the blended polymeric materials [203,204], An important factor in the development of new materials based on polymeric blends is the miscibility between the polymers in the mixture, because the degree of miscibility is directly related to the final properties of polymeric blends [205],... 

A partial miscibility between a linear polyimide and a crosslinked BMI was evidenced when the polyimides and the BMIs were prepared with the same diamine (Fig. 36) [116]. As a consequence the adhesive properties of the blend were better at high temperature than the ones of the linear polymer alone. 

Although the number of miscible blends is rapidly being increased, immiscibility is generally the result when unlike polymers are mixed. Consequently, a great deal of research has been and is being done on ways to improve the mechanical properties of immiscible blends. A widely practiced approach at the present time is to connect the minor dispersed phase to the major continuous phase through a covalent bond. This approach can take several forms. The oldest and most basic is to... 

Liu, J., Jean, Y.C., Yang, H. (1995) Free volume properties of polymer blends by positron annihilation spectroscopy Miscibility . Macromolecules. 28, 5774. 

Enhanced property demands in the packaging sector and also in the electric/ electronic and automotive sectors require improved product properties. Homogeneously miscible blends with, e.g., polyphenylene ether (PPE) combine the excellent processability of the amorphous polystyrene with the thermal stabilty of its blend partners. 

Improvement in cost, processability, and performance of polymers can also be achieved through blending two or more polymers. The blends may be homogeneous, heterogeneous, or a bit of both. Properties of miscible polymer blends may be intermediate between those of the individual components (i.e., additive behavior), as is typically the case for Tg. In other cases, blend properties may exhibit either positive or negative deviation from additivity. 

In blends composed of immiscible polymers, amorphous polymer does not affect the crystallization of crystallizable polymer, but if two polymers are miscible, amorphous polymer acts as diluent and affects crystallization of the second polymer. Poly(E-caprolactone) is a crystallizable component of the blend with poly( vinyl butyral), which is studied in compositions containing carbon black. Typically, blends of these two polymers form very large spherulites, and it is interesting to find out how carbon black affects crystallization and other properties of the blend as well as the distribution of carbon black in relationship to the spherulites. Figure... 

Macroscopic properties of polymer blends are influenced by the degree of mixing between component polymers [4, 5]. Miscibility is a term based on thermodynamics, and a miscible state means a homogeneous single phase on... 

Since miscibility (degree of mixing) influences macroscopic properties of a blend significantly, it is important to know the size and morphological information of domains in a blend. In Section 10.2.3.1, the effects of spin diffusion on Ti and Tip are discussed, which can be used to deduce the domain size on a scale of 2-50 nm. Sections 10.2.3.2, 10.2.3.3 and 10.2.3.4 discuss several experiments to monitor spin diffusion. To monitor spin diffusion, the following three periods, which are formally analogous to cross-relaxation and chemical exchange NMR experiments in liquids, may be required ... 

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