Rapid exfoliation and surface hydroxylation of high-quality boron nitride nanosheets enabling waterborne polyurethane with high thermal conductivity and flame retardancy

Boron nitride nanosheets (BNNS) hold significant promise as functional additives in thermal management materials for high-density and high-power electronic devices. However, due to the surface chemical inertness and strong "lip-to-lip" interactions between adjacent layers of hexagonal boron nitride, efficient exfoliation and simultaneous surface functionalization of BNNS remain a challenge. In this work, an innovative approach combines alkali-assisted hydrothermal treatment with high-speed shearing, achieving an impressive 65% yield of high-quality BNNS with a thickness of only 2.54 nm. Moreover, the hydroxyl functional groups were successfully introduced to BNNS surfaces, rendering them suitable for waterborne polyurethane (WPU) to create a multifunctional heat-conductive film. In 50-R8-BNNS/WPU film, achieved by simply mixing 50 wt% BNNS within WPU, a remarkable through-thickness thermal conductivity of 7.58 Wm-1 K-1 was attained, which is 30-fold increase compared to pure WPU. Moreover, this film exhibits remarkable thermal stability, excellent tensile strength, and fire safety performance, which is used as thermal interface materials for high-power LED and exhibits better thermal management capabilities compared to commercial silicone greases. The finding establishes a straightforward and efficient method for producing high-quality BNNS suitable for the composites of electronic thermal management applications.