Preparation of modified hexagonal boron nitride by ball-milling and enhanced thermal conductivity of epoxy resin

Hexagonal boron nitride (h-BN) is a new type of filler with high thermal conductivity, which has the potential to significantly improve the thermal conductivity of polymer matrix. The key is to surface modification and good dispersion of h-BN in polymer composites. In this study, a few-layer BN with surface modification was obtained by wet ball milling assisted with urea aqueous solution. The change of their lateral size, thickness and the content of functional groups were investigated as function of milling time from 2 h to 16 h. It was found that as the ball milling time increases, the modified BN show gradually reduced size and increased functional groups content. A mechanism for the modification of h-BN was proposed during milling: big size of BN is first broken into small size, then exfoliated into few layer and grafted with functional groups simultaneously. The modified BN with different milling times was used to improve the thermal conductivity of epoxy resin. It was found that the BN obtained by 8 h milling time had a best enhancement of thermal conductivity, which is about 3 times that of pure epoxy resin. In this case both the dispersion and BN size play role to determine the thermal property of BN reinforced epoxy. It was also found that the modified BN has a better improvement on the mechanical properties of epoxy composites compared with the pristine BN.