Firstly a short review of some frequently used models for fibre structures is given. Then a model, based on a three-dimensional monoclinic paracrystalline macrolattice is described. This model allows the calculation of the two-dimensional intensity distribution for the small-angle scattering from semicrystalline polymers with different orientational states. The parameters of the model result from comparison with the measured intensity. The method of analysis is applied to low-density polyethylene deformed uniaxially at different temperatures. The use of synchrotron radiation makes it possible to follow the destruction and rebuilding of the superstructure. A reversible change of the superstructure during stretching and relaxing was found for different draw ratios for very high-molecular-weight polyethylene samples.

The change of the superstructure of different polyethylenes during uniaxial deformation is investigated. The method used is small-angle scattering with synchrotron radiation. For branched polyethylene (Lupolen 18400) the whole deformation range is analyzed. Beginning with superstructure of the lamellar cluster type, the superstructure partly disappears on a time scale of a few minutes and the fibrillar structure is built up. The degree of destruction and rebuilding depends on the drawing temperature. For very high molecular weight polyethylene (GUR) a reversible change of the superstructure at higher deformation ratios and at different temperatures is observed. The superstructure of (ethylene-hexene) copolymers (TIPELIN) at high draw ratios depends on the drawing temperature and is almost independent of the side group content. lnterfibrillar microcracks parallel to the draw direction are produced in samples with a low side group content for draw ratios 1 3 1.5.