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. Issue 5 (March 2020) - Kuo, Chung-Feng Jeffrey
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 Al2 O3 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 2 g 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/cm 2 . 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 (>10 10 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.