Beyond filler loading: Morphology, interface, and proximity as governing factors for dielectric reliability in recycled alumina/epoxy nanocomposites

Epoxy-based nanocomposites are widely used in high-voltage insulation systems, where dielectric reliability is governed by local electric-field distribution. In this work, gamma, and alpha alumina nanoparticles were sustainably synthesized from recycled aluminum beverage cans and incorporated into epoxy resin to investigate the synergistic effects of morphology, surface functionalization, and particle proximity. Experimental results show that breakdown strength improves with filler loading up to an optimum of 5 wt.%, achieving enhancements of 47% for γ-Al 2 O 3 and 56% for α-Al 2 O 3 compared to neat epoxy. Numerical simulations reveal that γ-Al 2 O 3 induces morphology-dominated field intensification, while α-Al 2 O 3 exhibits orientation-dependent behavior. The introduction of a functionalized interfacial layer significantly reduces peak electric field by up to 53%. Proximity-controlled simulations demonstrate that severe field amplification occurs when the inter-particle gap decreases below 10 nm, indicating that dielectric failure is governed by proximity-critical configurations rather than filler loading alone. These findings establish the minimum inter-particle gap (g min ) as a key parameter linking nanoscale dispersion to macroscopic dielectric reliability.