Polymer Blends Containing Crystalline Polymers

Many of the polymer blends containing crystalline polymers involve crystalline polyolefins (e.g., polyethylene, polypropylene) and these blends will be discussed in Section 4.5. Additionally, crystalline engineering polymer blends, such as nylon 6,6, poly(butylene terephthalate), poly(aryl ether ketones), and poly(ethylene terephthalate), are blended with other engineering polymers (either amorphous or crystaUine) and these will also be discussed separately (see Section 4.6). Blends of the crystaUine engineering polymers with non-engineering polymers wiU be discussed in this section. AdditionaUy, crystaUine polyolefin blends with non-olefin polymers wiU be covered in this section. 

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Polymer Blends Containing Thermotropic Liquid Crystalline Polymer... 

The majority of polymer blends containing elastomeric, thermoplastic, and/or liquid crystalline polymers are processed by melt extrusion at some point in their history. After melt extrusion with intensive mixing, the morphology of an immiscible polymer blend on a microscopic scale will often consist of a dispersed phase of the more viscous polymer in a continuous matrix of the less viscous polymer (depending upon the relative amounts and viscosities of the two polymers in the blend). A good analogy from every-day experience is a dispersed mixture of viscous oil in an immiscible water matrix. 

This particular strategy is limited to those cases in which an immiscible polymer blend contains two semi-crystalline polymers that can co-crystalUze. Nadkarni and Jog [1989, 1991] have reviewed examples of this type of compatibilized blend. Co-crystaUization may also occur as a secondary process in an intimately mixed blend containing a copolymer with concomitant elfects on blend properties as shown in a few of the examples of this review. 

Polymer crystallization has been described in the framework of a phase field free energy pertaining to a crystal order parameter in which = 0 defines the melt and assumes finite values close to unity in the metastable crystal phase, but = 1 at the equilibrium limit (23-25). The crystal phase order parameter (xj/) may be defined as the ratio of the lamellar thickness (f) to the lamellar thickness of a perfect polymer crystal (P), i.e., xlr = l/P, and thus it represents the linear crystallinity, that is, the crystallinity in one dimension. The free energy density of a polymer blend containing one crystalline component may be expressed as... 

Her current research interests include studies of miscibility and physical aging in blends, nanophase separation in polymers with long side-chains, polymer dynamics, liquid crystalline polymers, composites, and systems containing nanoparticles. A common feature of these studies is the use of scattering techniques, especially neutron scattering, to study the local structure, conformation, and dynamics in polymers. She has written various reviews and book chapters in this area and has served on selection panels to allocate beam time at neutron facilities. 

Blizard, K. G., and D. G. Baird. 1987. The morphology and rheology of polymer blends containing a liquid crystalline copolyester. Polymer Engineering and Science 27 653-662. 

When dealing with crystallizable miscible polymer blends containing a noncrystallizable component, some refinements had to be made. Some modifications were proposed by Alfonso and Russell (1986) and by Cimmino et al. (1989) for blends in which the amorphous component is segregated into the interlamellar region (see also Sect. 3.2.2.1). First, the chemical potential of the liquid phase might be altered by the specific interactions that are often responsible for the miscibility of polymers (Olabisi et al. 1979). Such interactions may change the free energy required to form a critical nucleus as well as the mobility of both the crystalline and amorphous components. Second, the noncrystallizable component has to... 

The thermal history has a profound influence on the DSC curves of polymer blends containing at least one crystalline component. In order to obtain by DSC experiments, the samples are usually first heated to a temperature between the phase separation temperature and the melting point of the crystalline component and held for several minutes to remove the thermal history. 

Some examples of osmium tetroxide staining are worthwhile to discuss as they describe staining methods for specific polymers. Osmium tetroxide vapor was used to stain and harden (3 days) a thin film of a two phase blend containing crystalline polychloroprene [91]. The spherulitic texture was observed, likely by a combination of staining due to the unsaturation present and due to differential absorption by the crystalline and amorphous regions in the spherulites as the crystalline... 

Polymer blends containing a crystallizable component have attracted many scientists, both from basic research and applied research laboratories. This is probably due to the fact that the majority of commercially used thermoplastic blends and alloys contain at least one crystallizable material [5]. In order to obtain the desired product properties, it is often very important to control the crystallization process. For instance, in certain applications it is useful to have amorphous polyester (e.g., PET, as a package material), whereas for other applications a higher degree of crystallinity is necessary (e.g., as a fiber material). In amorphous/crystalline polymer blends the crystallization behavior is often strongly influenced by the amorphous component. Usually, the crystallization rate of the crystalline polymer is reduced by the amorphous polymer. In most systems this is caused by an increase... 

Hsieh T-T, Tin C, Simon GP. Miscibility and free volume behaviour of a number of polymer blends containing only thermotropic liquid crystalline polymers. Polymer 2000 41 4737-42. 

Generally, polymer chains exhibit a variety of flexibility, from flexible to rigid rodlike polymers. Polymer blends containing a liquid crystalline ordering have received considerable attention. The volume of literature on the theories and experiments of liquid crystallinity in polymer blends is now very extensive. There are many theoretical models for liquid crystalline polymers, such as the Flory lattice model [3-8], wormlike chain model [9-11], and Onsager virial theory [12] for rigid rods. An example of a recent review of liquid crystalline polymers is the text book of Donald and Windle [13[. 

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