Fabrication of flame-retardant and smoke-suppressant isocyanate-based polyimide foam modified by silica aerogel thermal insulation and flame protection layers

Because of containing urea groups, flame resistance and smoke releasing behaviors of isocyanate-based polyimide foam (IBPIF) produced using free foaming technology require further improvement. In this work, silica aemgel layers were incorporated into cells of IBPIF through an in situ growth process of silica sol (SS). Compared with silica aemgel particles directly mixed into the foaming slurry, the silica aemgel layers that firmly attached to the pores and surfaces of cells not only provided exceptional thermal insulation and flame protection, but also kept original cellular structure. With increase in ratio of SS mass to IBPIF volume, silica aemgel incorporation dosage was gradually increased. Accompanied by flame resistance was obviously improved and smoke releasing behavior was effectively suppressed. Those were indicated by the improved limiting oxygen index (LOI), decreased heat release rate (HRR), peak of HRR, and specific optical density of smoke (Ds) in trials with pilot flames. Compared with pure IBPIF, when the ratio reached to 5/15 g/cm(3), it resulted in LOI increasing from 22.0% to 33.0%, peak of HRR, total smoke production (TSP), and maximum value of Ds decreasing from 174 to 72 kW/m(2), 1.11 to 0.37 m(2)/m(2), 45.90 to 17.45, respectively.