Ball mill enhances the functionalization of boron nitride: The application for polyimide fillers

•Ball mill promotes functionalization of BN with amine molecules.•Ball mill parameters are essential to control the amount of functionalization on BN surface.•The functionalized BN can effectively strengthen the mechanical strength of polyimide films.•When the amount of functionalization was 8 wt%, the tensile strength and tensile modulus of PI composite films were the highest.