Crystalline polymers amorphous regions

Polymers are difficult to model due to the large size of microcrystalline domains and the difficulties of simulating nonequilibrium systems. One approach to handling such systems is the use of mesoscale techniques as described in Chapter 35. This has been a successful approach to predicting the formation and structure of microscopic crystalline and amorphous regions. 

The dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

Many polymers show partial crystallinity. This is apparent from the study of X-ray diffraction patterns, which for polymers generally show both the sharp features associated with crystalline regions as well as less well-defined features which are characteristic of disordered substances with liquid-like arrangements of molecules. The co-existence of crystalline and amorphous regions is typical of the behaviour of crystalline polymers. 

In the case of a semicrystalline polymer, the two components are the crystalline and amorphous regions. If we know the densities of the crystalline and the amorphous regions, we can calculate a sample s degree of crystallinity from Eq. 7.5. 

Rastogi, S. and Terry, A.E. Morphological implications of the interphase bridging crystalline and amorphous regions in semi-crystalline polymers. Vol. 180, pp. 161-194. 

Unlike simple inorganic compounds (e.g., NaCl or KC1), polymers do not have a perfectly ordered crystal lattice formation and are not completely crystalline. In fact, they contain both crystalline and amorphous regions. Hence, the X-ray diffractions from them are found to be a mixture of sharp as well as diffused patterns. 

Figure 13.3 also shows the orientation factors of the crystalline and amorphous regions as a function of take-up speed, which is pronounced in the case of a branched PET polymer. The shift towards increased freezing temperatures in branched polymer samples seems to be an indicator of higher elasticity (Figure 13.4). 

Figure 2.13 Schematic of the crystalline and amorphous regions of a semicrystalline polymer...

Most polymers consist of a combination of crystalline and amorphous regions. Even within polymer crystals such as spherulites (Figures 2.15 through 2.17), the regions between the ordered folded crystalline lamellae are less ordered, approximating amorphous regions. 

Polymeric solids such as polystyrene are most often noncrystalline. The random coil model would be most appropriate to describe such solids. In many polymers, both crystalline and amorphous regions are present in such materials, well-defined coiled regions are embedded in a randomly coiled matrix. 

Crystallinity In crystallization of polymers, the polymer forms crystalline and amorphous regions [2,4,25]. The formation of crystalline regions is accompanied by an increase in new vibrational modes caused by their crystal lattice interactions [2]. The IR spectrum of a given polymer differs by various absorption bands, depending on whether it is in the amorphous or crystalline state [2]. The IR spectrum exhibits regularity bands, splitting, and frequency shifts. Other absorption bands are not affected by crystallization and remain the same in both cases. Crystalline and amorphous bands can be used in the determination of the degree of crystallinity independent bands are useful for the determination of sample thickness [2],... 

A polymer may be amorphous, crystalline, or a combination of both. Many polymers actually have both crystalline and amorphous regions, i.e., a semicrystalline polymer. The Tg is a transition related to the motion in the amorphous regions of the polymer [3,8,9], Below the Tg, an amorphous polymer can be said... 

Polyolefins, especially polyethylene, can be cross-linked into a material that is elastic when heated. The structure of polyolefins, normally entangled long chains, includes crystalline and amorphous regions. Upon heating above the crystalline melting point of the polymer the crystalline regions disappear. 

Semicrystalline polymer A material consisting of a combination of crystalline and amorphous regions. Essentially, all common plastics and elastomers with the tendency to crystallize are semicrystalline. The degree of crystallization depends on the structure of the polymer and the conditions of fabrication. 

The morphology of solid polymers is also an important parameter. Thus, radiation-induced changes can be expected to differ in crystalline and amorphous regions — but in what way and to what extent "Crystallinity" and "amorphous" are not absolute terms and as more becomes known about the solid-state structure of polymers this should be related to radiation degradation. 

However, with naturally occurring macromolecules, such as cellulose, the older fringed micelle concept is believed to apply. This represents a crystalline polymer, (it would be more correct to speak of semicrystalline or partially crystalline polymers since a material consisting of chain molecules can never be completely ordered), made up of ordered (crystalline) domains interspersed with disordered (amorphous) domains, so that each polymer chain passes through several crystalline and amorphous regions (Figure 4). 

The polymer systems are often complex. For example, crystalline and amorphous regions coexist in semi-crystalline polymers. Any physical or chemical treatment of a polymer will induce structural changes, the knowledge of which is essential for a better... 

Morphological Implications of the Interphase Bridging Crystalline and Amorphous Regions in Semi-Crystalline Polymers... 

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