Synergistic enhancement of mechanical, thermal, and electrical properties in BNNS/Al2O3/epoxy composites via amino-terminated hyperbranched polymer-assisted interfacial engineering

Epoxy resin is widely used in electronic packaging and electrical insulation due to its excellent electrical insulation, dimensional stability, and processability. However, its application in high-power devices is limited by its intrinsically low thermal conductivity, high brittleness, and severe interfacial defects at high filler loadings. In this study, an amino-terminated hyperbranched polymer (AHAA) was first synthesized and introduced into an E51/methyl hexahydrophthalic anhydride epoxy curing system, and the matrix network structure was optimized by adjusting the AHAA content. The results showed that the system modified with 9 wt% AHAA (A9EP) exhibited the best overall mechanical properties and could therefore be used as the matrix for subsequent thermally conductive and electrically insulating composites. Furthermore, BNNS/Al 2 O 3 hybrid fillers were subjected to three-step interfacial grafting using tannic acid (TA), KH560, and AHAA to construct an AHAA-KH560-TA multilevel organic interfacial layer, and were compared with unmodified BNNS/Al 2 O 3 fillers. The multilevel interfacial modification significantly improved the dispersion of the fillers in the A9EP matrix and the interfacial bonding, thereby alleviating stress concentration and electric field distortion caused by high filler loading. The results showed that the tensile strength and flexural strength of FBA20/A9EP were 40.4 MPa and 100.97 MPa, respectively, with the breakdown strength of 92.12 kV/mm and the thermal conductivity of 0.607 W m −1  K −1 . This study indicates that the combination of AHAA-induced matrix regulation and overall TA/KH560/AHAA stepwise interfacial modification provides a feasible strategy for improving the mechanical, thermal, and electrical properties of epoxy composites.