Enhanced thermal resistance and ablation properties of ethylene-propylene-diene monomer rubber with boron-containing phenolic resins

With the development of aerospace industry, higher requirements have been put forward for the thermal properties of internal insulation materials for heat protection of solid rocket engine chamber. In this study, boron-containing phenolic resin (BPR) was chosen as the thermal-resistant filler of ethylene-propylene-diene monomer (EPDM). By adjusting the amount of BPR, a series of BPR/EPDM were prepared and their thermal, mechanical, and ablation properties were studied. The results showed that the addition of BPR significantly improved the char yield of EPDM. The char yield of BPR/EPDM was 21.6%, which increased by 17.9% (800 °C) relative to EPDM. By studying the structural evolution of BPR/EPDM during pyrolysis, boron oxide (B₂O₃) was formed, which avoided the formation of volatile carbon oxides and reduced the carbon loss. The molten B₂O₃ penetrated into the pores of carbonization products, which can protect the unstable edges of graphitic carbon and improve the ablation performance of BPR/EPDM. The linear ablation rate of BPR/EPDM was 0.045 mm/s (the lowest reported in current references). Additionally, the addition of BPR improved the graphitization degree of carbonization product. This research is expected to provide a resin matrix with excellent comprehensive performance and large-scale production for combustion chamber of the solid engine.