Ball-Milling Exfoliation of Hexagonal Boron Nitride in Viscous Hydroxyethyl Cellulose for Producing Nanosheet Films as Thermal Interface Materials

Boron nitride nanosheets (BNNS) exfoliated by physical or chemical methods frequently exhibit poor dispersity in common solvents due to incomplete exfoliation and a low degree of functionalization, which has severely impacted BNNS application performances as polymer and lubricant additives. In this work, we mechanically exfoliated the bulk boron nitride into nanosheets through a ball-milling method by adopting the viscous hydroxyethyl cellulose (HEC) solution as a medium. Because of the abundant hydroxyls and strong hydrogen bonding interactions with BNNS, the HEC can not only serve as an intercalator and a protective agent of the BNNS during ball milling but can also benefit the stable dispersion of the fabricated HEC/BNNS mixture in water. The HEC/BNNS aqueous dispersion obtained by directly pouring deionized water into the ball-milled product is easy to form a two-dimensional film via the solution-casting method. Because of the good exfoliation and dispersion of the BNNS in the HEC matrix, the HEC/BNNS films have high mechanical strength and thermal conductivity and have the potential to be used as thermal interface materials.