Distribution of Oriented Lamellar Structures in Injection-Molded High-Density Polyethylene Visualized via the Small Angle X-ray Scattering-Computed Tomography Method

Using the SAXS-CT method, which observed the spatialdistributionof nanometer-scale structures on a micrometer scale, we investigatedthe orientation distribution of the lamellar structure of injection-moldedHDPE. We reconstructed CT images in the plane perpendicular (X-Y) and the plane parallel to the injection direction(X-Z) from the SAXS intensities correspondingto the period of the lamellar structures. The CT image at a flow speedof 5 mm/s in the X-Y plane showed that thelamellar structures oriented in the injection direction mainly consistedof three layers: the skin layer, the subskin layer, and the core layer,based on their differences in the distribution states. The CT imagesin the X-Z plane showed that the distributionof the lamellar structures was oriented in the thickness directionin the subskin layer and part of the core layer. Furthermore, we observedthe distribution of the lamellar structure oriented in the injectiondirection with increasing injection speed, v, toevaluate the size change in each layer. The size of the skin layerthickness decreased heterogeneously in the CT images in the X-Y plane from v = 5 up to 40 mm/s.However, the distributions and thickness variations in the subskinand core layers were different from those in the skin layer due tothe balance of the elongation, relaxation, and fountain flow effects.