A novel controllable expansion insulation material reinforced with EMs for SRMs: Synergistic optimization mechanism of ablation resistance and thermal insulation performance

To resolve that the lightweight, ablation resistance and thermal insulation of thermal insulation materials for solid rocket motors (SRMs) are difficult to synergistically improve, an innovative strategy of "high-temperature responsive controllable expansion" is proposed. Expandable microspheres (EMs) were introduced into the EPDM rubbers to prepare a new type of controllable expansion insulation material. These materials maintain a dense and continuous structure during manufacturing stages. And they can form uniform cell structure through in-situ expansion of EMs when exposed to high temperatures, realizing the dynamic synergistic improvement of thermal insulation and ablation resistance. It is shown that the EPDM-165 formula has the optimal comprehensive performance. The linear ablation rate decreases by 43.8%, the charring rate decreases by 13.4%, and the maximum backside temperature decreases by 29.5% compared with the basic formula. In the ablation motor test, the charring rate in the high-speed section is reduced by 40.7% compared with the basic formula. By controlling the formation time of the cell structure, this study effectively circumvents the problems of loose char layer and reduced ablation resistance of traditional foaming materials. It provides a new technical path for the performance breakthrough of thermal insulation materials for SRMs. It should be noted that the controllable expansion insulation materials have the limitation of performance degradation under long-term ablation conditions. And further optimization is required by improving the heat resistance of EMs and regulating the stability of the cell structure.