Preparation of boron nitride nanosheets using a chemical exfoliation method as a thermal conductive filler for the development of silicone thermal composites Part I: effect of single- and hybrid-filler additions on the silicone composite performance

Abstract

This study developed a nano-size filler as a thermally conductive filler for a silicone thermal pad (STP) by exfoliating hexagonal-boron nitride (h-BN) with the chemical exfoliation-free radical polymerization method to produce boron nitride nanosheets (BNNSs). We used N,N-dimethylacrylamide as the intercalation agent. After polymerization, it became poly(N,N-dimethylacrylamide) to exfoliate the h-BN layer. BNNSs were taken as a single-filler and hybrid-fillers with Al₂O₃ and then compared with h-BN to investigate their effect on the silicone composite properties. As the free radical polymerization reaction time increased, the interlayer distance of BNNSs lengthened to 0.35 nm, while the thickness of h-BN sheets decreased. The X-ray diffractometer results showed how the h-BN (002) crystal plane was enhanced and displaced. The Fourier transform infrared spectra showed that the characteristic peaks of 1372 and 812 cm⁻¹ were enhanced, and the Raman results showed that the E_2g displacement and full width at half maximum increased, thus validating the successful preparation of BNNSs. Based on the scanning electron microscope-transmission electron microscope results, BNNSs with 24-hour reaction time offered the best results with a thickness of 5 nm. The highest thermal conductivity reached 3.66 W m⁻¹ K⁻¹ with the addition of 50 wt% BNNSs, and tensile strength of up to 11.30 kg/cm². Hybrid-fillers showed enhancement of thermal conductivity to 5.28 W m⁻¹ K⁻¹ and tensile strength to 7.32 kg cm⁻². Finally, the STP showed that the volume resistance (>10¹⁰ Ω cm), withstand voltage (>10 kV mm⁻¹), and flame resistance (V-0) of the STP prepared by this study comply with the industrial application specifications.