| Abstract
| - Several commercial and noncommercial, high- and low-density and ultraoriented polyethylene samples, as well as polyethylene samples with inorganic fillers, have been investigated by inversion−recovery cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (NMR). In allthese samples two types of all-trans chains in orthorhombic crystalline domains are detected, which givetwo overlapping carbon-13 lines with different line widths and different relaxation times. From the NMRrelaxation parameters we conclude that one type of the crystalline chains, which composes 60−90% ofthe crystalline fraction in all samples, can execute at room temperature 180° flips with a frequency inthe kilohertz domain. The other crystalline chains are more rigid and probably are found in more perfectstructures in which such chain flips do not occur or occur on a much slower time scale. Adding kaolinefiller particles to polyethylene enhances the contribution of the more mobile crystalline chains. Thepresence of the two distinctly different types of crystalline environments is found in all polyethylenesamples investigated so far (more than 25 samples).
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