Characterization of injection molded HDPE using SAXS and WAXS

Abstract

Plastic materials are used in many of our every day commodities. Its structure may vary depending on which material it consists of and the applied process conditions. The present work was carried out to contribute to the knowledge of the material structure of a certain plastic material called high-density polyethylene, or HDPE, produced through a manufacturing process called injection molding. The project was carried out in collaboration with Tetra Pak® that uses HDPE as a component in their packages. The aim of the thesis was to characterize the structure of the material HDPE during mechanical deformation. When the material is being produced the shearing forces within the material in injection molding leads to a distribution of different microstructures through the thickness of the material. The structures of the material’s full thickness as well as the different layers, that were formed during molding, were investigated. The structure of undeformed HDPE is relatively well-know, and this work investigated how the structure changed after the material was subject to a mechanical deformation. To get deeper insight into such changes, the material was furthermore investigated with in-situ testing, of structural changes during mechanical deformation. The experimental characterization was performed by means of Small- and Wide- Angle X-ray scattering (SAXS and WAXS) using both laboratory X-ray sources and synchrotron X-ray sources. The scattering experiments showed different microstructures of HDPE on different length-scales. The structures on different length-scales could be distinguished before and after the material had been deformed. During the uniaxial in-situ tensile tests, the deformation sequence of the structures could be monitored, and give an explanation of material behavior under mechanical stress. This information contributes to the general understanding of deformation of plastic materials.