Charge trapping sites in spherulitic polypropylene

Charged areas of spherulitic polypropylene (PP) samples were visualized by a simple technique of attaching oppositely charged fine dye particles. A co mbination of this visualization technique and thermally stimulated current (TSC) spectroscopy was applied to identify the regions where shallow and de ep charge traps exist densely in positively corona-charged spherulitic PP. The shallow and deep traps in the PP sample are directly related to its two TSC bands, B-L and B-H, appearing at temperatures around 60 degrees C and above 100 degrees C, respectively. From visualized charge patterns of the P P samples with and without thermal cleaning of the B-L band, it was found t hat the shallow traps mainly exist in the boundaries and the peripheral reg ions of spherulites while the deep traps are located in the central parts. Furthermore, the relative numbers of the shallow and the deep traps in the PP spherulites were estimated and found to depend on spherulite size: the r atio of shallow to deep traps decreased from 60/40 for 130-190 mu m spherul ites to 43/57 for 320-400 mu m spherulites.