Crystalline regions of polymers

Crystalline regions of polymers can be represented as combinations of folded chains forming lamellar structures. Amorphous regions are less ordered than crystalline regions. Additional orientation of polymer chains occurs. This results in increased strength in the order of the orientation. 

Crystallinity refers to a regular, ordered, three-dimensional crystal lattice portion of a polymer (Kroschwitz, 1990) where the polymer chains align themselves in perfect parallel array. There are no purely crystalline polymers, as all polymers, even so-called crystalline polymers, have some portion of amorphous content. Nonetheless, crystalline regions of polymers can form up to 98% of the polymer structure (Rosen, 1993) and have consequent large impacts on mechanical behavior. 

Wriggling, or vibrations of atoms about equilibrium positions. For crystalline regions of polymers, this vibration is about a fixed position, while for amorphous polymers the motion is about a less-ordered atomic center. 

The non-crystalline regions of polymers are usually called amorphous, but they may sometimes have some kind of organisation and they may certainly be oriented, as discussed in chapters 10 and 11. They are the... 

The structure of the crystalline regions of polymers can be deduced from wide-angle X-ray diffraction patterns of highly stretched specimens. When the stretching is uniaxial the patterns are related to those obtained from fully oriented single crystals. The crystal structure of polyethylene was determined by Bunn [7] as long ago as 1939 (Figure 1.10). 

Two factors lead to increase in the crystallinity of polyimides. One is the simple combination of only two monomer units, which facilitates the packing necessary for good crystallinity. Another factor is the flexibility required for the fold-back observed in crystalline regions of polymers. 

SOLUBILITY COEFFICIENT AND DIFFUSION COEFFICIENT Solubility coefficient is a measure of the amount of penetrant absorbed by the polymer from a contacting phase. It represents polymer sorption capacity with respect to a particular sorbate. Diffusion coefficient, on the other hand, is a measure of the mobihty of penetrants within the polymer. Gas diffusion rate in crystalline region of polymers is usually negligible compared to that in the amorphous region. Values of solubility and diffusion coefficients depend on various factors such as size of penetrant, polymer-penetrant interactions, polymer morphology, glass transition temperature, and so on. Both solubility and diffusion coefficient typically exhibit Arrhenius-type dependence on temperature ... 

The structure of the crystalline regions of polymers can be deduced from wide-angle X-ray diffraction patterns of highly stretched specimens. When the stretching is uniaxial. 

TEM is a very effective technique to study the morphology of polymer samples. TEM can be also used to identify the crystalline regions of polymer and the spherulitic structure of polyethylene composites. Many studies on agglomeration and dispersion of nano-particle in PE based nanocomposites have been carried out by TEM [54, 55]. 

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