Acrylonitrile butadiene rubber‐based heat shielding materials for solid rocket motors: Impact of metal–organic frameworks on thermal and mechanical properties

The thermal protection system (TPS) plays a major role in shielding solid rocket motors (SRMs) against structural failure from excessive heating. This study was directed at the recent innovation in flame‐retardant materials used for thermal insulation, with a particular focus on integrating metal–organic frameworks (MOFs) to bolster thermal stability. Three targeted transition metal‐BDC MOFs (MIL‐88(Fe), MOF‐71(Co), and MOF‐5(Zn)) were hydrothermally synthesized and the effect of incorporating these MOFs into nitrile butadiene rubber (NBR) composites was tracked. In general, the addition of the MOFs improved the interfacial compatibility and the processing of the composites. Additionally, experimental investigations have shown that all MOFs improved the mechanical properties of the NBR composite materials. Specifically, the addition of MOF‐5 has been found to increase the maximum tensile strength to 13 MPa, while MIL‐88 increased the elongation at break to 67.1%. In order to evaluate the thermal stability and ablative resistance of the prepared composites, the oxy‐acetylene flame test was utilized. Results showed that the efficiency of the composite as thermal insulation is highly dependent on the MOF type and the metal included. The impact of MOF‐71(Co) on thermal insulation displayed the least linear and mass ablation rates (0.0168 mm/s and 0.057 g/s, respectively) along with the lowest recorded back‐face temperatures, owing to the formation of a thick and compact char layer upon exposure to flames.