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 aerogel layers were incorporated into cells of IBPIF through an in situ growth process of silica sol (SS). Compared with silica aerogel particles directly mixed into the foaming slurry, the silica aerogel 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 aerogel 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/cm3, 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/m2, 1.11 to 0.37 m2/m2, 45.90 to 17.45, respectively. • Layered silica aerogel with heat insulation and fire resistance could firmly attach to the pores and surfaces of IBPIF cells. • With increase in ratio of M(SS)/V(IBPIF), silica aerogel incorporation dosage was gradually increased. • By the situ sol-gel growth, the cell structure of IBPIF could not be changed even when silica aerogel was added to 131.8%. • As silica aerogel dosage and thickness added, IBPIF flame resistance was enhanced, and smoke release behavior was inhibited. • As M(SS)/V(IBPIF) was 5/15 g/cm3, IBPIF LOI value was 30%, smoke maximum specific optical density was reduced by 62%. [ABSTRACT FROM AUTHOR]