Development of alumina-reinforced elastomeric composites via additive manufacturing

Vat photopolymerization (VPP) enables the fabrication of high-resolution elastomeric components with complex geometries and excellent surface quality. However, the relatively low mechanical strength and durability of commercially available elastomeric resins limit their broader structural and functional applications. Enhancing mechanical performance while preserving the inherent deformability of elastomeric materials remains a significant challenge, particularly in particle-reinforced systems where filler addition often increases porosity and defect sensitivity. This thesis investigates the development of alumina-reinforced elastomeric composites fabricated via VPP and examines the influence of filler morphology on processing behavior, microstructural evolution, and mechanical performance. Two alumina morphologies were evaluated: platelet-shaped alumina with a high aspect ratio and sub-micron crushed alumina particles. Composite formulations containing 3 wt.%, 6 wt.%, and 9 wt.% filler were prepared and characterized through rheological analysis, UV–Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), porosity measurements, tensile testing, hardness measurements, and cyclic loading experiments. The crystallographic texture of the alumina particles within the printed composites was quantified using the Lotgering factor (LF), enabling a direct comparison of morphology-dependent orientation behavior. Platelet-reinforced composites exhibited pronounced preferential alignment during the VPP process, reaching Lotgering factor values of approximately 0.55, whereas sub-micron alumina showed little or no preferred orientation (LF ≈ 0). The platelet systems generally exhibited lower porosity and improved structural consolidation compared with the corresponding sub-micron formulations. A clear relationship was established between particle morphology, orientation, porosity, and mechanical response. The 3 wt.% platelet-reinforced composite exhibited the best overall performance, increasing the ultimate tensile strength from 12.4 MPa for the neat resin to 45.7 MPa while simultaneously maintaining high deformability and nearly doubling the elongation at break. Cyclic loading experiments further indicated improved retention of mechanical properties at intermediate platelet loadings. In contrast, the sub-micron alumina systems produced only moderate improvements because of limited particle alignment and increased defect sensitivity. The primary contribution of this work is the systematic comparison of platelet-shaped and sub-micron alumina reinforcements under identical VPP processing conditions and the establishment of quantitative correlations between particle morphology, crystallographic orientation, porosity, and mechanical performance. The results demonstrate that platelet-shaped alumina provides a highly effective reinforcement strategy for elastomeric VPP composites and offers practical design guidelines for developing lightweight, compliant, and mechanically robust additively manufactured components for applications such as flexible devices, wearable technologies, energy-absorbing structures, and other advanced engineering systems.