Problems relating to long period determination in polyethylene shish-kebab structures

The X-ray long periods from high molecular weight injection molded polyethylene (PE) with a shish-kebab structure have been compared with values derived from electron micrographs. It is shown that while small angle X-ray scattering (SAXS) presents two long periods, the direct measurements from transmission electron microscopy (TEM) furnish only the lower SAXS periodicity. In an attempt to clarify this discrepancy of results, laser light diffraction and Fourier transformation of electron micrographs have been undertaken. Using this method two long periods are found in all regions investigated. Results are discussed in terms of the role played by the structured or “weakly crystalline” interlamellar parts, containing a lower electron density, which are neglected by the small angle scattering of X-rays and which give rise in particular regions to larger scattering periodicities.