Low phosphorus-containing hydrophobic silica aerogels with high thermal stability and outstanding flame retardancy

To enhance the thermal safety of hydrophobic silica aerogel (SA), we synthesized a high thermal safety SA utilizing phytic acid (PA) as a catalyst. Tests confirmed that the SA/PA maintain low density (0.09 g/cm3) and low thermal conductivity (23.2 mW/m/K). The thermal stability and combustion characteristics of SA/PA were evaluated by thermogravimetric analysis (TG), gross calorific value (GCV) and cone calorimeter. The TG data clearly show that the addition of PA can greatly increase the decomposition temperature of silylmethyl by 208.1°C and the residual char content to 92.6%. The GCV results show that a small amount of PA could greatly reduce the GCV of SA, with a maximum decrease of 51.6 %. Information from cone calorimeter data affirmed that PA can decrease the burning factors by decreasing the total heat release and peak heat release rate by 63.6% and 28.7%, respectively. The flame retardant mechanism of PA against SA was scientifically examined by thermogravimetric-infrared-mass spectrometry analysis and residual char analysis. In the gas phase, PA by capturing radicals produced during the combustion process of the material, the combustion chain reaction is quenched. In the condensed phase, PA promotes the rapid dehydration and carbonization of SA to establish a physical barrier and achieve flame retardancy. Our findings highlight the beneficial impact of PA on SA. The aerogel exhibited enhanced thermal stability and effective flame retardancy after PA treatment.