Comparative Wide-angle X-ray and Microscopical Studies on the Layered Structure in Injection Molded Polypropylene Disks

Abstract

Abstract Circular disks (280 mm diameter, 2 mm thickness) were injection molded from isotactic polypropylene under systematic variation of processing parameters (melt temperature, mold temperature, screw velocity, packing pressure, and packing time). Sections were taken from the disks perpendicular to their surface, at 40 mm distance from gate, in different orientations, and were investigated by means of optical microscopy using polarized light and by spatially resolved wide-angle X-ray scattering. The results from X-ray scans of the cross-sections are presented in terms of several parameters characterizing the state of orientation of α-PP crystallites and the relative amount of β-PP crystallites. The profiles of the various X-ray parameters versus the distance from surface deliver a detailed picture of the layered structure of the cross-sections which is supported and supplemented by micrographs taken with polarized light. The comparison of the results obtained for disks molded under different conditions unveils clear correlations between processing parameters and morphological characteristics of the disks.