Injection-molded polymeric nanocomposites with aluminum flakes: an assessment of optical and mechanical properties

Polymeric nanocomposites containing aluminum flakes have been widely studied in the past to achieve the production of plastic components with metallic finish. However, a deeper investigation into their properties is not present in literature yet. Hence, with the aim of expanding their range of applications, this thesis describes an extensive study of the influence of process and materials parameters on a set of properties for polymeric nanocomposites with aluminum flakes for different injection molding configurations. The production was carried out both via standard injection molding and Rapid Heat Cycle Molding (RHCM). The selected matrices are Acrylonitrile Butadiene Styrene (ABS), Polymethylmethacrylate (PMMA) and Polypropylene (PP). A Design of Experiment (DoE) plan was adopted to draw statistical conclusions, mainly concerning the effect of the process – e.g., melt and mold temperature, injection speed and packing pressure – and materials – e.g., flakes’ diameter and concentration – parameters on the targeted properties. The latter were predominantly specular reflectivity, surface roughness, local and bulk mechanical properties. These characterizations enabled the observation of matrix-dependent effects and showed how to optimize the process to reach certain goals. In addition, evaluations of the flakes’ features as sold are discussed to link their properties to the ones of the whole nanocomposite. Experimental and computational workflows were also elaborated to estimate the alignment of the flakes along the specimens’ cross section. Based on existing scientific literature, it had not previously been possible to quantitatively estimate the orientation profile of thin (< 200 nm) flakes in a nanocomposite. Further steps were taken towards describing the effect of the geometric arrangement of the flakes in the matrix on the specular reflectivity of the material through the use of ray tracing simulations. Since the orientation of flakes inside the matrix is inevitably connected to the shear rates that are generated as a consequence of the polymer flow, rheological characterizations were carried out. Overall, this research highlighted how the properties of the final nanocomposite are mainly linked to the properties of the matrix, the diameter of the employed flakes and the temperature of the mold.