Polymer semicrystalline, morphological

C), it has been observed that its crystallization from the melt is enhanced [103-106], Melt crystallized polymers nucleated with n-s polymer-CD-ICs crystallize more rapidly, evidence greater levels of crystallinity, higher melt crystallization temperatures, and semicrystalline morphologies characterized by crystals which are smaller and more uniformly distributed than in un-nucleated pure bulk samples. 

The properties of block copolymers, on the other hand, cannot be calculated without additional information concerning the block sizes, and whether or not the different blocks aggregate into domains. The results of calculations using the methods developed in this book can be inserted as input parameters into models for the thermoelastic and transport properties of multiphase polymeric systems such as blends and block copolymers of immiscible polymers, semicrystalline polymers, and polymers containing various types of fillers. A review of the morphologies and properties of multiphase materials, and of some composite models which we have found to be useful in such applications, will be postponed to Chapter 19 and Chapter 20, where the most likely future directions for research on such materials will also be pointed out. 

This chapter, related to the crystallization, morphological structure and melting of polymer blends has been divided into two main parts. The first part (section 3.1) deals with the crystallization kinetics, semicrystalline morphology and melting behavior of miscible polymer blends. The crystallization, morphological strucmre and melting properties of immiscible polymer blends are described in the second part of this chapter (section 3.4). 

In the following part, a discussion on the crystallization behavior in immiscible polymer blends is given, including the nucleation behavior, spheiuhte growth, overall crystallization kinetics, and final semicrystalline morphology. Each topic is illustrated with several examples from the literature, to allow the reader to find enough references on the discussed subject for further information. 

The discussion on the crystallization behavior of neat polymers would be expected to be applicable to immiscible polymer blends, where the crystallization takes place within domains of nearly neat component, largely unaffected by the presence of other polymers. However, although both phases are physically separated, they can exert a profound influence on each other. The presence of the second component can disturb the normal crystallization process, thus influencing crystallization kinetics, spherulite growth rate, semicrystalline morphology, etc. 

Table 3.23. Overview of literature in which the final semicrystalline morphology in immiscible crystaUine/amorphous polymer blends has been studied...

Several authors have investigated the influence of compatibilization on the global blend morphology. However, only a few authors really tried to understand the effect of compatibilization in crystalline/crystalline polymer blends on the crystallization kinetics, melting behavior and semicrystalline morphology of the components. In Table 3.29 some recent results on this topic are summarized. 

The scientific literature on crystallization in polymer blends clearly indicates that the crystallization behavior and the semicrystalline morphology... 

The third design feature is the polymer microstructure. Morphology of polymer can influence wear resistance of polymers. For example, in a semicrystalline polymer, both amorphous and crystalline phases coexist. The amorphous phase has been shown by Tanaka (8) to be weaker than the crystalline phase, thus the former wears faster than the latter. In addition to the difference in phases, the size of the spherulites and the molecular profile can also influence the wear rates. Thus, a control of the morphology through crystallization can improve the wear resistance of a polymer such as polytetrafluoroethylene (11). 

The processes that occur in the spinline, between the exit of the polymer from the spinneret and the point of stress isolation on the first godet or roller at the base of the spin line, involve the changing of this fluid network to the solid-state molecular chain topology of the filament. Within a distance of 3 5 m, and under the influence of an applied force (take-up tension) and quench media, at speeds in excess of 100 miles per hour—less than 0.01 sec residence time—the fiber is transformed from a fluid network to a highly interconnected semicrystalline morphology, characterized by the amount, size, shape, and net orientation... 

In the solid state, chitosan is a semicrystalline polymer. Its morphology has been investigated and many polymorphs are mentioned in the literature. Single crystals of chitosan were obtained using fully deacetylated chitin of low molecular weight. The dimensions the orthorhombic unit cell of the most common form were determined as a = 0,807 nm, h = 0,844 nm, c = 1,034 nm the unit cell contains two antiparallel chitosan chains, but no water molecules (Dash et al., 2011). 

The scientific literature on crystallization in polymer blends clearly indicates that the crystallization behavior and the semicrystalline morphology of a polymer are significantly modified by the presence of the second component even when both phases are physically separated due to their immiscibility. The presence of the second component, either in the molten or solid state, can affect both nucleation and crystal growth of the crystallizing polymer. The effect of blending on the overall crystallization rate is the net combined effect on nucleation and growth. 

In the formation of crystals, polymer chains fold back and forth to form the crystalline lamellae. The crystalline lamellae and the amorphous phase are arranged in semicrystalline morphological entities, ranging from a micron to several millimeters in size. The most common morphologies that can be found in injection-molded polymers are spherulites, which usually form under quiescent conditions, and shish-kebab structures, which may appear under shear flow [see, for example, Eder and Janeschitz-Kriegl (1997), Zuidema et al. (2001) and Janeschitz-Kriegl (2009)]. 

HetGfOgGnGOUS Oxidation. Oxidation of a polymer in service is a reaction between the solid polymer and a reactive gas, oxygen. In polyolefins the situation is complicated by the semicrystalline morphology. It is important to ask whether oxidation can be treated as effectively homogeneous and subject to the normal rules of liquid-phase kinetics, or whether the oxidation is more heterogeneous. 

Fibers, Latex Particles, and Polymer Processing, in addition to the typical morphologies displayed by semicrystalline polymers, the morphologies formed or present in polymers used in important applications or subjected to various processes, namely fibers (141) and latex particles (187), were investigated by SFM. 

In contrast to amorphous polymers, the structural details of semicrystalline polymers can also be visualized using diffraction phenomena (X-ray scattering or electron diffraction in electron microscopes). Depending on the processing, several other special semicrystalline morphologies are possible, such as shish kebab structures, oriented lamellae, microfibers, or spiral lamellae for details see Chapter 2 in Part 11. 

Semicrystalline polymers constitute an important group of polymers with a very broad range of applications, in particular, the family of polyolefins, including poly-ethylenes and polypropylenes, is one of the most prominent commodity plastics that make up a great part of the world s plastic market. The rapid development of new catalysts has allowed for the tailored design of macromolecules with defined semicrystalline morphologies and thus defined properties. Besides these commodity plastics, there are a number of technical and functional polymers that have a typical semicrystalline structure (e.g., PEEK, PVDE, PTFE). 

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