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.