Flame-Retardant and Smoke-Suppressed Silicone Foams with Chitosan-Based Nanocoatings

Flexible silicone foams (SiFs) are high-performance but flammable materials that emit dense smoke in a fire. Two type of low-cost, eco-friendly nanocoatings, i.e., chitosan (CH)/ammonium polyphosphate (APP) and CH/montmorillonite (MMT), were fabricated on SiFs through a layer-by-layer (LbL) assembly. With seven bilayers (BL) of CH/APP coatings, the limiting oxygen index (LOI) increases from 20.2% to 23.8%, the peak heat release rate (pHRR) decreases by 27.6%, and the total smoke production (TSP) decreases 42%. Further deposition of CH/APP, however, partly damaged the fire resistance. In contrast, fire hazard and smoke release of CH/MMT coated SiFs were monotonously reduced. Every 7 BL of coating leads to ca. 12% reduction of TSP. Moreover, thermogravimetric analysis (TGA) was used to follow the pyrolysis of the coated foams, and scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX) were applied to analyze the char residues systematically.