The Principle of Polymer Blending

As discussed in Chapter 2 of this Handbook, there is a significant difference in the rate of phase separation and the generated morphology when a single-phase blend is quenched into either the 

For proper understanding of the immiscible polymer blends it is important to take into account the interphase. In binary blends, the interphase thickness, is inversely proportional to the interfacial tension coefficient, thus, poorer the miscibility, larger the interfacial tension coefficient and smaller the interphase thickness. Owing to the thermodynamic forces the polymeric chain-ends concentrate at the interface and the low molecular weight components difiuse to it as well. Thus, 

The interphase thickness depends on the miscibility of the polymeric component as well as on the compatibilization. For uncompatibilized binary, strongly immiscible systems, the interphase thickness Al - 2 nm. The thickest interphase has been observed for reactively compatibilized polymer alloys Al = 65 nm. For most blends, the interphase thickness is in between these two limits. The importance on the interphase can be appreciated noting that its volume will be the same as that of the dispersed phase when the drop diameter (without interphase) is about 500 nm. It is noteworthy that in most commercial polymer alloys the drop diameter is about five times smaller, making the importance of the interphase much greater. 

Only in rare cases (mixtures with 0.1, or compositions near the phase inversion) the compatibilization may not be necessary. However, even in these cases compatibilization has beneficial effects on blends performance. All the other immiscible blends should be compatibilized. 

The compatibilization must 1. Reduce the interfacial tension to facilitate dispersion, 2. Stabilize the generated morphology against modification during the subsequent processing steps, and 3. Enhance adhesion between the polymers domains, facihtating the stress transfer, hence improving the mechanical properties of the product. The methods of compatibilization are discussed in details in Chapter 4. Interphase and compatibilization by addition of a compatibilizer, and in Chapter 5. Reactive Compatibilization of this Handbook. 

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Even the outstanding mechanical properties of natural products are based on the principle of polymer blends, like, for example, wood, which is composed in a complicated way of cellulose and lignin. 

To obtain well performing material out of a mixture of immiscible polymers two principal operations must be performed compatibilization and compounding. Fundamental aspects of these will be discussed in Part 16.3 The principles of polymer blending. However, interested reader is advised to search detailed information is specific chapters of this Handbook, viz. on compatibilization in Chapters 4 and 5, on flow, morphology and compounding in Chapters 7, 8 and 9, respectively. 

This second group of tests is designed to measure the mechanical response of a substance to applied vibrational loads or strains. Both temperature and frequency can be varied, and thus contribute to the information that these tests can provide. There are a number of such tests, of which the major ones are probably the torsion pendulum and dynamic mechanical thermal analysis (DMTA). The underlying principles of these dynamic tests have been covered earlier. Such tests are used as relatively rapid methods of characterisation and evaluation of viscoelastic polymers, including the measurement of T, the study of the curing characteristics of thermosets, and the study of polymer blends and their compatibility. They can be used in essentially non-destructive modes and, unlike the majority of measurements made in non-dynamic tests, they yield data on continuous properties of polymeric materials, rather than discontinuous ones, as are any of the types of strength which are measured routinely. 

Since its introduction some years ago, inverse gas chromatography (IGC) has been recognized as a convenient route to the determination of thermodynamic interaction parameters for polymeric or other non-volatile stationary phases in contact with selected vapor probes (1,2). The principles of IGC experiments have also been extended to two-component stationary phases (3), thereby making it possible to specify thermodynamic interaction parameters for the components of polymer blends (4,5), as well as for filled polymers and other mu 11i-component systems. Despite these attractive features, limitations must by recognized on the general... 

The use of infrared spectroscopy for the characterization of polymer blends is extensive (Olabisi et al. 1979 Coleman and Painter 1984 Utracki 1989 He et al. 2004 and references therein Coleman et al. 1991, 2006). The applicability, fundamental aspects, as well as principles of experimentation using infrared dispersive double-beam spectrophotometer (IR) or computerized Fourier transform interferometers (FTIR) were well described (e.g., Klopffer 1984). 

Rodgers, B, and Ryba, (, (1995) Principles of polymer blending. Paper V presented at the 147 Meeting of the Rubber Division, American Chemical Society, Philadelphia,... 

A full discussion of the thermodynamics of polymer blends is beyond the scope of this review and only some essential, and frequently discussed, aspects are presented here in order to provide the reader with some principles of the thermodynamics of polymer blends. 

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. 

Volume 1 is devoted to fundamental principles of polymer blends and is divided into eight chapters. These chapters cover the basic thermodynamic principles defining the miscible, immiscible, or compatible nature of amorphous, semi-crystal-hne and Uquid crystalline polymer blends, and temperature and composition dependent phase separation in polymer blends. They are detailed below and build upon each other. 

As the screw turns, it conveys the pellets from the feed zone towards the melting zone. A combination of external heating and mechanical work melts the polymer as it is transported towards the metering zone. The metering zone pumps a uniform stream of molten polymer to a forming device, such as a profile die. Other types of extruders that employ two or more screws are commonly used for compounding polymer blends. The principles of twin screw extrusion will be discussed in Chapter 12. 

The first papers describing an LC LC separations of polymer blends due to the barrier effects were published in the mid-1990s [226,227] and the explanation of separation principle was originally presented in 1996 [231]. The review of both LC LC procedures and systems, as well as their first applications can be found in Ref. [28]. 

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