Site-resolved X-ray scattering studies,I investigations on plates from PP-graphite composites

Cross-sections cut from rectangular plates injection or compression-molded from composites of isotactic polypropylene and varying amounts (up to 40 mass%) of different grades of graphite were investigated by site-resolved wide-angle X-ray scattering (WAXS), using a two-circle goniometer and a specially adapted Kratky camera, respectively. The measurements yielded detailed information about the orientation of both the filler particles and the PP crystallites, in dependence on the position in the cross-sections. In the plates molded from composites, the graphite particles are preferentially oriented with their (002) planes parallel to the surface of the plates and the α-PP crystallites prefer the same orientation for their (040) planes. In plates devoid of graphite, the PP crystallites show a different orientation behavior, however, the presence of 0.2% graphite is already sufficient to change the orientation to the afore-mentioned mode. The observed parallelism in the preferential orientation of the graphite particles and the PP matrix suggests the assumption of hetero-epitaxial growth of α-PP crystallites on the (002) surface of oriented graphite particles. According to our results, the effects of the PP-graphite interaction are dependent on the nature and properties of the graphite particles and may be modulated by treating the graphite surface with different coatings.