Hexagonal boron nitride as the foaming agent to improve the flexibility of polyimide-derived graphite films with high thermal conductivity

The excellent thermal conductivity of graphite films makes it an ideal thermal management material in the field of electronics. Flexibility is an important property for preparing polyimide (PI)-derived graphite films with high thermal conductivity. In the study, hexagonal boron nitride (h-BN) was used as a foaming agent to improve the flexibility of PI-derived graphite films. A series of graphite films were prepared via carbonization and graphitization of self-synthesized polyimide films using h-BN as the foaming agent. The influence of different amounts of h-BN on the structure, flexibility, and thermal conductivity of graphite films was studied in detail. Compared with pure PI-derived graphite film, the flexibilities of h-BN/PI-derived graphite films improved significantly. The flexibility improvement mechanism of graphite film using h-BN as foaming agent was also proposed. The vaporization of BN powders at ultra-high temperature results in the pressure difference between inside and outside of the graphite layers, and then the graphitic “bubbles” were formed on the graphite film. The semicircular “bubbles” created by h-BN sublimation could provide enough adjustment space for the shear slip, and some of the forces around the pores could be partially offset. According to the results, the graphite film derived from the 0.06 wt% h-BN/PI composite film owe the best comprehensive performance, including excellent flexibility, relatively high thermal diffusivity and high in-plane thermal conductivity. This research has important application value in the field of heat dissipation of electronic devices. Graphical abstract