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

Injection molding is known to create a layered anisotropicmorphologyacross the sample thickness due to varying shear and cooling ratesduring the manufacturing process. In this study, scanning small-angleX-ray scattering was used to visualize and quantify the distributionof hierarchical structures present in injection-molded parts of low-densitypolyethylene (LDPE) with varying viscosities. By combining scatteringdata with results from injection molding simulations and tensile testing,we find that oriented shish-kebab structures, as well as elongatedspherulite structures consisting of semicrystalline ellipsoids, contributeto high ultimate tensile strength along the flow direction. Furthermore,we show that a higher degree of orientation is found close to theinjection gate and in LDPE with higher viscosity, consequently fromelevated shear and cooling rates present during the injection moldingprocess.

Automated summary

Injection molding leads to layered anisotropic morphology across sample thickness due to varying shear and cooling rates. This study used scanning small-angle X-ray scattering to observe and quantify the hierarchical structure distribution in injection-molded low-density polyethylene (LDPE) parts with different viscosities. The combination of scattering data, injection molding simulations, and tensile testing revealed that oriented shish-kebab structures and elongated spherulite structures consisting of semicrystalline ellipsoids contribute to high ultimate tensile strength in the flow direction. Moreover, a higher degree of orientation is found near the injection gate and in LDPE with higher viscosity, caused by elevated shear and cooling rates during the injection molding process.