Effective non-halogen flame-retardants combined with nSiO2 particles to improve thermal stability and fire resistance of high-performance polyurethane nanocomposite foams

•Nanosilica (nSiO2) from rice husk was successfully synthesized and characterized.•PU foam/nSiO2/flame retardant additives nanocomposites were successfully synthesized.•Thermal stability and fire resistance of nanocomposite were significantly improved.•Microstructure, thermal conductivity and mechanical properties were deeply analyzed. This study focuses on the improvement of the thermal stability and flame-retardant performance of polyurethane (PU) foam by using effective flame-retardant additives and nano silica (nSiO2) particles from rice husk. The addition of non-halogen flame retardants (FRs) including aluminum trihydroxide (ATH), triphenyl phosphate (TPP), and diammonium phosphate (DAP) leads to markedly enhanced thermal stability and fire resistance of the PU/nSiO2/FRs nanocomposites, resulting in achieving UL-94 HB standard. In particular, the nanocomposites met the UL-94 V-0 criteria thanks to the inclusion of DAP at 25 phr. The LOI value of the nanocomposites reached 26 % which is much higher than that of PU/nSiO2 nanocomposite, about 20 %. In order to further understand the fire-proof mechanism, the residue char layer remaining of the PU/nSiO2/FRs nanocomposites after being burned was also investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR). In addition, the microstructure, thermal stability, thermal conductivity, and mechanical properties of nanocomposites were also evaluated in this study.