Solid-state deformation/forming

The most important parameters in solid-state deformation are the polymer forming temperature, the rate of deformation, the deformation and the tension or pressure. The effect of the polymer temperature is illustrated in Figure 2 in the case of the extrusion. An increase in the extrusion temperature leads to a decrease of the total pressure required... 

This section deals with semicrystalline thermoplastics that cannot be processed by the techniques described earlier. Perkins and Porter (22) have reviewed the solid state deformation of polymers in detail and describe the numerous reports of solid state extrusion. Aharoni (23) has reported that a number of polymers may be solid state extruded to high draw ratio (> 10) by the conventional process. These include HOPE, poly(ethylene oxide), poly(4-methyl pentene-1). Polypropylene is also readily extrudable (24). However, there are many other polymers that would be attractive if they could be obtained in high draw, particularly the established fiber-forming polymers such as the nylons and poly(ethylene terephthalate). The ma,ximum extrusion draw ratio that has been reported for nylon 6 is 5 (25). This has been attributed to the onset of strain hardening at much lower extensions than polyethylene (10). Ultrahigh molecular weight polyethylene is also of interest as a way of improving the mechanical properties. 

In the context of this discussion, solid-state deformation will encompass any orientation that takes place at temperatures below the final melting temperature of the polymer. Such deformation may be imposed on samples that are initially isotropic or anisotropic. During commercial forming processes, such deformations are usually taken to the point at which a stable morphology is formed, i.e., beyond the yield point. For a general description of the macroscopic phenomena associated with solid-state deformation, the reader s attention is directed to the section on mechanical properties in Chapter 5. 

Solid-state deformation normally results in the destruction of the crystallites of the original morphology, followed by reordering to form new crystallites. Newly formed crystallites are themselves subject to disruption at higher orientation levels, being replaced by a hbrillar morphology. The proposed mechanisms of solid-state deformation are discussed separately in a subsequent section. 

SOLID. Matter in its most highly concentrated form, i.e., the atoms or molecules are much more closely packed than in gases or liquids and thus more resistant to deformation. The normal condition of the solid state is crystalline structure—the orderly arrangement of the constituent atoms of a substance in a frame work called a lattice, See also Crystal. Crystals are of many types and normally have defects and impurities that profoundly affect their applications, as in semiconductors, The geometric structure of... 

Solidification and deformation processes are very seldom used to fabricate bulk articles from ceramics and other materials with low ductility and malleability. These substances are brittle and suffer fracmre before the onset of plastic deformation. Additionally, ceramics normally have exceedingly high melting points, decompose, or react with most cm-cible materials at their melting temperatures. Many ceramics are worked with in powder form since the products of most solid-state chemical syntheses are powders. Fabricating a bulk part from a powder requires a consolidation process, usually compaction followed... 

In the solid state, amino acids exist in the zwitterionic form, E (Fig. 4.5). The primary ammonium group, NH3+, exhibits a broad band 3040 cm-1 and two bands common to amino acids at 2500 and 2100 cm-1. Strong bands at 1665 and 1590 cm-1 for the COO- asymmetric and symmetric stretches, respectively, and NH3+ deformations at 1550 cm-1 are also typical of amino acids. A full assignment for glycine is found in Nakamoto.10 The metal-bound COO- and NH2 groups will show characteristic shifts in these stretching frequencies. 

The theory of electronic excitation, which occurs during plastic deformation and fragmentation of crystals, is discussed by Molotskii [99]. The mechanochemistry of inorganic solids has been reviewed by Boldyrev et al. [100] with particular reference to the work done in The Institute of Solid State Chemistry at Novosibirsk. The consequences of mechanical activation on the structures and properties of selected spinels have been examined and the rate of the reaction forming barium tungstate investigated. Prospects for the future development of this subject are assessed. 

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