Site-resolved X-ray studies on bicomponent injection molded polypropylene plates

Rectangular plates were bicomponent injection molded from various grades of isotactic poiypropyientl (PP) which differed in the molecular properties and were used as core and skin components in several different combinations. Site-resolved wide angle X-ray scattering (WAXS) studies on cross-sections elucidated the layered structures in the plates in dependence on the distance from the gate and on the combination of core and skin material. The results are presented in terms of various depth profiles for alpha- and beta-PP crystallites, supplemented by longitudinal profiles and by micrographs taken with polarized light. The comparison of results obtained for different pairs of core and skin components reveals characteristic differences in the orientation behavior of the various PP grades used and in the patterns of layered structures formed. The results are related to the molecular properties of the polymer and to the flow conditions of the melt during mold filling, and may serve as a basis for constructing appropriate simulation models.