Enable synergistic improvement of thermal conductivity, tensile performance, and hardness of boron nitride and aluminum oxide nanofillers in DLP 3D-printed composites

Advances in micro- and nanotechnology have accelerated the need for thermally efficient, additively manufactured functional materials, yet the intrinsically low thermal conductivity of photopolymer resins remains a critical bottleneck for next-generation 3D-printed electronic and heat-dissipative systems. This study incorporated low-content aluminum oxide ( Al 2 O 3 , 50 nm) and boron nitride (BN, 1 μm) fillers into a commercial polyurethane acrylate (PUA) resin using Digital Light Processing (DLP). A comprehensive characterization (thermal conductivity, TGA/DTG, tensile testing, Shore-D hardness, KLA-Tencor surface profiling, SEM-EDS, and FTIR) quantified the isolated and synergistic effects of fillers (1–1.5 wt%). BN outperformed Al₂O₃ as a single filler (thermal conductivity gains 6–9% vs. 2–3%), while synergistic BN/Al₂O₃ formulations delivered the best balance. The synergized formulation (RAB-6; 1 wt% BN + 1.5 wt% Al₂O₃) reached 0.216 W·m⁻¹ ·K⁻¹ at 30 °C (≈9.1% above neat PUA) and showed an additional ≈ 8.9% increase at 150 °C. Synergy improved thermal stability (onset temperature shifts up to ≈9%) and residual char (RAB-6 residual ≈14.6%), and reduced decomposition rate (from 0.972% to 0.940%/°C), indicating improved high-temperature resilience. These thermal gains incurred measurable mechanical trade-offs, Al₂O₃ tended to agglomerate, increasing surface roughness substantially (up to +148% for synergized formulation) and reducing ductility (RAB-6 showed a ∼22% reduction in tensile strength and a ∼28% drop in elongation for certain formulations). Nonetheless, modulus losses were modest for the synergized formulations (≈–3% relative to neat PUA) while hardness increased slightly. Low-content synergizing via a solvent- and treatment-free DLP process presents a scalable pathway to lightweight, thermal interface components, customized electronic housings, and printed circuit encapsulations where thermal management and mechanical reliability are essential.