Polymeric ablative materials (PAMs) are widely used in spacecraft currently for thermal insulation. However, it is challenging to find a single filler that can improve both ablative and mechanical properties of PAMs. In this study, a new type of hybrid cross‐linked polyphosphazene microspheres (PHC) is added to ethylene propylene diene monomer (EPDM) composites as a filler for the first time and its influence on the ablation, mechanical, and thermal properties of EPDM is investigated. The results show that the addition of 3 phr PHC increases the ablation performance by about 10% and enhances the mechanical properties by 20% approximately. In addition, the ablation mechanism is studied in accordance with SEM, FTIR, and Raman spectroscopy. On the one hand, PHC has the effect of catalyzing carbonization, thus increasing the rate of residual carbon; on the other hand, PHC changes the morphology of the char layer, forming a cross‐linked structure containing P─O─Si bonds on the surface. The findings regarding catalyzing carbonization and the special char layer structure could guide the design of ablative materials.

Many advanced fillers were used in ethylene propylene diene monomer (EPDM) insulation composites to enhance the ablative resistance by strengthening char layer. However, the structures of fillers and char layer were usually neglected. In this work, a new type of cross-linked network-like polyphosphazene nanotubes (PNTs) was added in EPDM composites in combination with graphene. The results showed that the ablation performance of EPDM composites was improved by 21.6% with the synergistic effect of PNTs and graphene.Moreover, the ablation mechanism was studied by analyzing ablated char layer using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and Raman spectroscopy. PNTs served as skeleton to build the cross-linked network char layer and graphene played a role in enhancing the properties of char layer. The findings of this work emphasize the synergistic effect of structures and properties of fillers when performing ablative modification, which provides a new idea to enhance the ablation properties of EPDM composites.