Improvement in Ablation and Thermal Properties of Ultra-lightweight Silicone/Cork Composites Insulator Using Novolac Aerogel

Hypothesis: Thermal insulating materials are essential in optimization of energy consumption and to reduce heat and energy loss. Lightweight thermal insulator materials can reduce weight/density and improve the performance of final product. One of the ways to approach lightweight thermal insulator is to develop porous polymeric nanocomposites with low density and good thermal insulation properties. Cork is a cellulosic material with microcells that are widely used in lightweight thermal insulating applications. Porous structure in cellulosic cork allows it to be chosen as an adequate thermal insulator, especially in aerospace applications. Since cork has low density and very low thermal conductivity, many research works are conducted to reduce its thermal conductivity and improving its thermal stability.
In order to improve the thermal insulation performance and ablation of silicone/cork composite, a novolac aerogel nanostructure was used. Novolac aerogel had a nanoporous structure with very low density, thermal conductivity and thermal diffusivity. The presence of novolac aerogel in the microcell structure of cock and filling its porous spaces led to higher density of the cork, eliminated the air thermal convection process in its microcells, and it therefore decreased the thermal conductivity and thermal diffusivity of the composites, significantly.
Finding: The mechanism of heat transfer elimination of novolac aerogel by convection could decrease the thermal conductivity and thermal diffusivity of silicone/cork composites by 39% and 45%, respectively, due to pore size reduction. Also, the aerogel could increase thermal stability and thermal resistance and the residual char with adequate thermal stability. Moreover, a resole/graphene oxide coating layer on the composites surface could significantly improve the composites thermal ablation. Under these conditions, the back surface temperature of composite in the presence of aerogel nanostructure decreased by 55%.