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Sheared isotactic polypropylene (iPP) forms a special crystalline assembly called branched shish kebab. The effects of two colorants, Cu-phthalocyanine and ultramarine blue, on the branched shish-kebab structure have been investigated by using synchrotron wide-angle x-ray scattering. The effects of the colorants on the morphological distributions of iPP are well constructed through the shear field or temperature gradient, including crystallinity, molecular orientation, fraction of lamellae, and thickness of crystalline lamellae. It is found that the Cu-phthalocyanine can significantly affect the morphological development of sheared iPP but the ultramarine blue cannot. In the presence of Cu-phthalocyanine, the degree of crystallinity is increased, the molecular orientation is enhanced, the more a*-axis-oriented components form, and the crystalline lamellae are thickened. [ABSTRACT FROM AUTHOR]

Abstract: Small-angle X-ray scattering (SAXS) studies were carried out to investigate effects of sodium benzoate (SB) on the shear-induced distributions of lamellar structures through the depth direction of injection-moulded isotactic polypropylene (iPP) plates, using the micro beam available from a synchrotron to gain good spatial resolution. It was found that in the presence of SB, the shish–kebab structure emerges over a broader range to include regions in which a random arrangement of crystalline lamellae is found without SB. The oriented crystalline lamellae are even found in positions that are very close to the core center. The SB-induced shish–kebab structure under low levels of shear flow is attributed to lower free energy barriers for the coil-to-stretch transition and shorter times to start the crystallization. The effect of SB on the lamellar dimensions is significant only in the core region, and only when the concentration of SB is sufficiently high. A down-U distribution of the long spacing is found, which is mainly ascribed to the variation of thickness of crystalline lamellae with the depth. The results show that a higher level of lamellar orientation is not necessarily accompanied by a higher degree of linear crystallinity. [Copyright &y& Elsevier]

Synchrotron small-angle X-ray scattering (SAXS) studies were carried out to investigate effects of thickness of injection-moulded isotactic polypropylene (iPP) plates on shear-induced morphology and morphological distribution through the depth direction of the plates. Different levels of effective shear flow are imposed on the iPP melt by changing the thickness of the plates although the injection moulding is performed with the same injection ram speed and the same melt and mould temperatures. Shish-kebab-like morphology is found roughly 100 μm from the surface of plates, regardless of the thickness of plates. However, the type of shish-kebab-like morphology is very sensitive to the thickness. The shish-kebab structure at the surface region can be changed into the kebab-structure only or random crystalline lamellae as the thickness of the plate increases. The preferential orientation of crystalline lamellae along the flow direction strongly depends on the thickness of the plate, although the melt-shear does not significantly enhance the degree of linear crystallinity. It is also found that in the core region, the slow relaxation of polymer chains in the thick plate results in a higher degree of linear crystallinity. The results indicate that the shear-induced morphology is strongly dependent on effective shear flow and should be described individually. [Copyright &y& Elsevier]