Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene

Abstract

Injection molding is known to create a layered anisotropic morphology across the sample thickness due to varying shear and cooling rates during the manufacturing process. In this study, scanning small-angle X-ray scattering was used to visualize and quantify the distribution of hierarchical structures present in injection-molded parts of low-density polyethylene (LDPE) with varying viscosities. By combining scattering data with results from injection molding simulations and tensile testing, we find that oriented shish-kebab structures, as well as elongated spherulite structures consisting of semicrystalline ellipsoids, contribute to high ultimate tensile strength along the flow direction. Furthermore, we show that a higher degree of orientation is found close to the injection gate and in LDPE with higher viscosity, consequently from elevated shear and cooling rates present during the injection molding process.