Plastic Deformation of Polypropylene. III. Small-Angle X-Ray Scattering in the Neck Region

Abstract

The small‐angle x‐ray scattering (SAXS) pattern of polypropylene (PP) drawn at various temperatures (Td = 20°, 100°, and 135°C) was investigated in a range of very closely spaced draw ratio (λ) values through the neck region. In the zone before the neck starts (λ = 1.05–1.1) the uniform diffraction ring due to microspherulitic material with a long period L 0 changes into a four‐point diagram superposed onto an elliptical halo. At the beginning of the neck (λ = 1.3–2.5) two meridional maxima arising from a new fibrous structure with a limiting long period LT appear. Irrespective of whether L 0>LT or L 0<LT the transition between L 0 and LT is discontinuous. The four‐point pattern reminiscent of the spherulitic structure remains observable up to the end of the neck. In the same manner as in the case of PE, stacks of lamellae exhibiting the most favorable orientation for chain tilt and slip start being plastically deformed and finally break into folded‐chain blocks which are incorporated into microfibrils. The fracture occurs in a thin destruction zone which separates the new microfibrils from the not yet transformed stack of original lamellae. Because of the morphological inhomogeneity of the spherulitic sample, the destruction zones and, hence, the starting points of the microfibrils are rather randomly scattered in the neck region and do not merge into one single layer extending over the whole cross section of the sample.