| Abstract: | Structural foam specimens, consisting of three co-axial cylinders of different diameter and length, were injection-molded from isotactic polypropylene, mixed with 0.5 wt% azodicarbonamide as blowing agent, by the classical low-pressure process in a mold cavity (temperature 20°C) pre-pressurized with nitrogen, at melt temperatures of 200, 220, and 240°C, applying different sprue systems and injection directions. Cross-sections were cut from the middle of each cylinder in longitudinal orientation and investigated by site-resolved wide-angle x-ray scattering, making use of the so-called “parallel transmission” geometry. The measurements yielded detailed information about the orientation, dimensions, and interplanar spacings of α-PP crystallites, the distribution of β-PP, and the crystallinity in the cross-sections of the moldings and led to the establishment of general relations between the molding conditions and the microstructure of the moldings in dependence on the configuration of the specimens. |
