Thermal conductive epoxy adhesive with binary filler system of surface modified hexagonal boron nitride and α-aluminum oxide

In this work, we prepared the epoxy-based adhesives with a binary filler system, which was composed of organosilicon modified hexagonal BN (h-BN) and α-Al₂O₃. H-BN platelets and α-Al₂O₃ nanoparticles were decorated by aminopropyltrimethoxysilane (APTMS) and glycidylpropyltrimethoxysilane (GPTMS), respectively, to form covalent links to the filler/polymer matrix interface. The surface chemical composition was investigated by Fourrier transform infrared spectroscopy (FTIR) and thermogravimetry analysis (TGA), which demonstrated that the modifiers were successfully grafted onto the surface of fillers. This modification has been confirmed beneficial to thermal conductivity so that the thermal conductivity of adhesives incorporated with modified binary fillers could reach 0.85 w/m k, which is 10% more than specimen filled with unmodified fillers, because covalent links strengthened the interface and prohibited heat diffusion. Modified Hashin–Shtrikman model was utilized to analyze thermal resistance of the binary filler system, indicating that adhesives filled with modified fillers displayed lower thermal resistance. The enhancement of interface also brought about some other positive effect, especially in the decreasing of dielectric constant (< 4.3 at 1000 Hz) and the low values of dielectric loss tangent (10^–3) and high electronic resistance (> 10¹⁴). Furthermore, the mechanical strength is significantly improved when the modified binary fillers were used.