Fabrication methods melt casting

Fabrication methods have overwhelmingly focused on improving nanotube dispersion because better nanotube dispersion in polyurethane matrix has been found to improve the properties of the nanocomposites. The dispersion extent of CNTs in the polyurethane matrix plays an important role in the properties of the polymer nanocomposites. Similar to the case of nanotube/solvent suspensions, pristine nanotubes have not yet been shown to be soluble in polymers, illustrating the extreme difficulty of overcoming the inherent thermodynamic drive of nanotubes to bundle. Therefore, CNTs need to be surface modified before the composite fabrication process to improve the load transfer from the polyurethane matrix to the nanotubes. Usually, the polyurethane/CNT nanocomposites can be fabricated by using four techniques melt-mixing (15), solution casting (16-18), in-situ polymerization (19-21), and sol gel process (22). 

Although in principle this route can be used for the production of both glasses and polycrystalline ceramics, in practice it is hardly ever used for glasses because of the availability of more economical fabrication methods (e.g., melt casting). It is, however, by far the most widely used method for the production of polycrystalline ceramics. The various processing steps are shown in Fig. 1.15. In its simplest form, this method involves the consolidation of a mass of fine particles (i.e., a powder) to form a porous, shaped powder (referred to as a green body or powder compact), which is then fired (i.e., heated) to produce a dense product. Because of its importance and widespread use, the fabrication of polycrystalline ceramics from powders will form the main focus of this book. In the next section, we provide an overview of the fabrication of polycrystalline ceramics from powders which will form the basis for the more detailed considerations in subsequent chapters. 

Extmsion technology is used to produce spunbond, meltblown, and porous-film nonwovens. Fabrics produced by these systems are referred to individually as spunbonded, meltblown, and textured- or apertured-film nonwovens, or genericaHy as polymer-laid nonwovens. These fabrics are produced with machinery associated with such polymer extmsion methods as melt-spinning, film casting, and extmsion coating. In polymer-laid systems, fiber stmctures are simultaneously formed and manipulated. 

Purely physical polymer blends are most commonly prepared by either mechanical mixing (melt) or dissolution in a common solvent followed by casting and solvent removal. In this study, both techniques were used the latter method was more readily applicable for film formation in small-scale laboratory batches. It was recognized that certain morphological differences between melt- and solution-fabricated polymers are often observed these include phase inversions and distortions, especially with graft and block polymers. However, casual observation by optical and electron microscopy revealed no dramatic differences between the melt- and solution-cast films, and this cannot be readily explained. 

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