Study on the Thermal Conductivity and Insulation Properties of Polyimide Composite Films Filled With Surface-Coated BNNs

Polyimide (PI) is widely utilized in high-power electronic devices due to its outstanding thermal stability, superior mechanical strength, excellent electrical insulation, and chemical resistance. However, its intrinsically low thermal conductivity hinders its application in highly integrated systems. To address this limitation, the present study successfully prepared KH550-functionalized Boron Nitride Nanosheets (BNNs@KH550)/Polyimide composite films through a combined method of ball milling and silane coupling agent KH550 surface modification, aiming to develop advanced film materials that meet the stringent requirements of high-power electronics. XPS analysis confirmed the successful grafting of KH550 onto the BNNs surface, which significantly improved the dispersion uniformity of BNNs within the PI matrix and effectively suppressed agglomeration. In terms of performance, the KH550 modification demonstrated positive effects: contrasting with the continuous decline in breakdown strength caused by unmodified BNNs, the BNNs@KH550/PI film exhibited a slight enhancement in breakdown strength, reaching 543.3 kV/mm at a low filler loading of 2 wt%, and maintained the dielectric dissipation factor at an extremely low level, nearly identical to that of pure PI. Furthermore, the composite film's thermal conductivity significantly increased with the BNNs@KH550 doping content, reaching 0.39 W/(m·K) at a 5 wt% loading. Regarding mechanical properties, the KH550 modification markedly enhanced the composite film's tensile strength; at a 5 wt% loading, the film's tensile strength (60.42 MPa) showed an 11.3% increase compared to the unmodified control group (54.27 MPa), strongly confirming that KH550 reinforces interfacial adhesion and promotes efficient stress transfer. This study provides a simple yet effective surface modification and fabrication strategy, offering support for the development of PI-based composite materials that possess excellent thermal management, electrical insulation, and mechanical properties.