HIGH-MODULUS POLYETHYLENE FIBER STRUCTURE AS SHOWN BY X-RAY-DIFFRACTION

High-quality X-ray diffraction patterns were obtained from small bundles and single fibers of Polyethylene at both small and wide angles using a synchrotron X-ray source. The equatorial streak in small angle (SAXS) can be used to give the length, width, and misorientation of the scattering objects, while the shape of wide-angle spots gives the same information about the crystals. The SAXS objects are 150-200 nm long, longer than the crystal length. This is in accord with microfibril models where the crystals are not continuous. The fibril interfaces are significantly less well oriented than the crystals within them. This seems anomalous, but the misorientation could correspond to tapered or irregular fibrils. The crystals are 15-30 nm across, but in some samples the fibrils are apparently only 6 nm across on average. The widths could really be the same if the fibril size distribution is broad or if fibril volume fraction has been underestimated. The method of analyzing the SAXS equatorial streak can be applied to any reasonably well oriented fiber that has a fibrillar structure.