Lightweight polyimide/silica aerogel composite foams and their derived carbon foams for excellent flame retardancy, thermal insulation and EMI shielding performance

Multifunctional porous materials demonstrate ubiquitous applications in the fields of flame retardancy, thermal insulation and electromagnetic interference (EMI) shielding. In this work, a series of lightweight polyimide/silica aerogel (PIF/SiA) foams with exceptional thermal stability, flame retardancy and thermal insulation performance were prepared by employing microwave-assisted foaming and thermal imidization treatment, using polyester ammonium salt/silica aerogel (PEAS/SiA) powders as the derivative precursors. The limiting oxygen index and fire growth rate reached as high as 58.2% and as low as 0.1 kW/(m2·s) for PIF/SiA composite foams, respectively, which was a result of the formation of micro/nano multi-scale pore structure of PIF skeleton and the "pearl-necklace-like" skeletal network of nano SiA. In addition, the PIF/SiA composite foams exhibited excellent thermal insulation and infrared stealth performance, which demonstrate a potential for long service life in fire protection use. Furthermore, the carbonized PIF/SiA (i.e., PICF/SiA) foams possessed enhanced mechanical (improvement of 117.6%) and EMI shielding performance (specific EMI shielding effectiveness: 8541.9 dB/(g/cm2)) when compared with the original PIF/SiA composite foams. To sum up, a facile method was proposed to fabricate multifunctional PIF-based composite foams and their derived carbon foams for flame retardancy, thermal insulation and EMI shielding applications in high-end engineering sectors.