Spherulite structure, deformation morphology, and mechanical properties of isotactic polypropylene fibers

This study delineates the complex morphological-deformation processes that occur during the spinning, fabrication, and testing of a series of drawn yarns as an integrated picture of mass movement on all morphological levels. The study involved the use of nine different experimental techniques, including small-angle light scattering, small-angle and wide-angle x-ray diffraction, micro x-ray diffraction, birefringence, interference microscopy, and sonic-modulus, density, and tensile measurements. A prerequisite of the study was a clarification of the morphological structure of three-dimensional bulk isotactic polypropylene spherulites. The bulk spherulite was found to have a morphological structure (a axis parallel to the radius) consistent with the observed bulk morphology of fibers and films. Two-dimensional Type III spherulites were similarly examined; their crystallites were found to be of the β form. As a result of the broad experimental approach to fiber-deformation morphology used in this study the significance of the often ignored interspherulitic-deformation mechanisms to fiber processes becomes apparent, the importance of the wide-angle x-ray, azimuthal intensity distribution for the characterization of inhomogeneous-deformation processes is demonstrated, and an oriented-microvoiding process is observed to be an important deformation mechanism.