Study on flame retarded flexible polyurethane foam/alumina aerogel composites with improved fire safety

In this article, a novel strategy has been proposed for the preparation of polyurethane/alumina aerogel (FPU/Alag) composites with homogeneous dispersion of alumina aerogel. The FPU/Alag composites have been prepared via immersing FPU foams into alumina sols followed by a freeze-drying method. Fire safety performance of the FPU composites with various Alag compositions in terms of thermal properties and flammability performance were evaluated. The composites demonstrated an earlier thermal degradation but higher thermal stability with increasing temperature and greater char yields than pure FPU. Total heat and smoke release, and rate of smoke emission of the FPU/Alag composites were found to be greatly reduced in comparison with those of FPU. Morphology and thermal conductivity (κ) properties of FPU/Alag composites and their corresponding residual char were investigated. The κ values of the composites were measured to be higher than that of FPU due to the accumulation of alumina flakes on the cell-walls of FPU. In contrast, the κ values of the char were lower than that of the calcinated alumina aerogel (C-Alag) counterpart, due to the formation of side by side, partially-opened compartments isolated by alumina flakes. Nitrogen adsorption analysis showed that C-Alag had a specific surface area of 211.5 m2/g and mesoporous volume of 0.28 cm3/g. The remarkable improvement in fire safety of FPU foams with the addition of Alag could be attributed to the combined effects of thermal-insulating, retention and adsorption of C-Alag that was in-situ formed inside FPU matrix during the combustion process.