Improved mechanical, thermal properties and ideal dielectric properties of polyimide composite films by incorporation of boron nitride nanosheets and aramid nanofibers

Abstract In this work, a high‐performance composite film polyimide (PI)/boron nitride nanosheets (BNNS) + aramid nanofibers (ANFs) was prepared by in‐situ polymerization. Modified two‐dimensional (2D) BNNS were prepared by urea‐assisted ball milling to exfoliate and NH 2 functionalize hexagonal boron nitride(h‐BN) in one step. One‐dimensional (1D) ANFs prepared by deprotonation method and 2D BNNS were simultaneously incorporated into PI and used as effective reinforcement nanofillers. This novel PI/BNNS + ANFs composite film has excellent thermal stability and mechanical properties. Compared with pure PI, the glass transition temperature ( T g ) increased by approximately 18°C, and the coefficient of thermal expansion (CTE) decreased by 11.45%. Remarkably, the tensile strength and elongation at break of PI/BNNS + ANFs‐1 wt% composite film increased by 18.6% and 133.4%, respectively. The improvement of thermal stability and mechanical properties were ascribed to the uniform dispersion of BNNS + ANFs and the interfacial interaction between BNNS + ANFs and PI matrix. Furthermore, the PI/BNNS + ANFs composite films show good dielectric properties and optical transparency. These excellent comprehensive properties of the PI/BNNS + ANFs composite films make it a good candidate for the flexible substrate.