Lightweight and anisotropic polyimide-based composite foams for efficient flame retardancy, thermal insulation and electromagnetic interference shielding applications

There is a growing need for lightweight porous materials that combine cushioning and shock absorption, high-temperature fire protection, thermal insulation and electromagnetic properties in extreme engineering environments. Herein, a simple strategy was employed to combine polyimide foam (PIF) and silica aerogel (SiA) to prepare a series of polyimide/silica aerogel (PI/SiA) composite foams with anisotropic structure and properties. The anisotropic micrometer-scale foam pore structure and the three-dimensional nano “pearl-necklace-like” porous structure collectively constructed the hierarchical porous structure, endowing PI/SiA composite foams with enhanced mechanical and thermal properties. The unique anisotropic porous structure conferred PI/SiA composite foams with improved mechanical strength in the vertical direction and superior mechanical flexibility in the horizontal direction. In addition, the prepared PI/SiA composite foams exhibited outstanding thermal stability and self-extinguishing flame retardancy, with an initial thermal decomposition temperature and a limiting oxygen index reaching as high as 587.7℃ and 67.7%, respectively, demonstrating promising application prospects in high-temperature fire protection fields. The PI/SiA composite foams also displayed excellent thermal insulation and anisotropic thermal management performance, with a low thermal conductivity of 0.0275 W/(m·K) and a large surface temperature difference of 131.9℃. Moreover, the high-temperature pyrolysis residue of PI/SiA composite foams (i.e., PIC/SiA composite foams) exhibited anisotropic electromagnetic interference (EMI) shielding performance, with the EMI shielding effectiveness and specific EMI shielding effectiveness in the horizontal direction reaching as high as 50.5 dB and 10194.0 dB/(g/cm 2 ), respectively. Thus, polyimide-based composite foams with excellent mechanical, thermal and electromagnetic properties hold broad application prospects in extreme environments.