Polyethylene, crystallites high-density

Polyethylene, crystallites in, 1215 high-density, 1210 high-molecular-weight, 1210 kinds of, 1210 low-density, 1210 synthesis of, 240-241 ultrahigh-molecular-weight, 1210 uses of, 242... 

In some cases it is not possible to fit the data to a simple model in which there are only two phases, crystalline and non-crystalline it is necessary to assume the presence of an intermediate interfacial phase. For instance, in a particular set of spin-diffusion experiments on polyethylene the data could be fitted to a three-phase model in which the thickness of the interfacial region was found to be 2.2 0.5 nm both for low- and for high-density polymers, compared with thicknesses of about 9 and 40 nm, respectively, for the crystallites. 

Crystalline polymer a polymer with ordered structure, such as high-density polyethylene (HDPE) and cellulose. Semicrystalline polymers consist of regions of crystallinity or crystallites dispersed in amorphous regions. 

Since polymer chains are packed together more efficiently and tightly in crystalline areas than in amorphous areas, crystallites will have a higher density. Thus, low-density (0.92 g/cm ) polyethylene is estimated to be about 43% crystalline, while high density (0.97 g/cm ) polyethylene is about 76% crystalline. Density is, in fact, a convenient measure of the degree of crystallinity. Because the volumes of the crystalline and amorphous phases are additive, density and degree of crystallinity are related by... 

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