An Autonomously Self-Healing Silicone Polyurea Waterproof Coating for Combustible Cartridge Cases

Nitrocellulose-based combustible cartridge case (NC-3C) is highly hygroscopic, which greatly limits its broader application. The effective strategy for NC-3Cs to prevent moisture is the endowment of waterproof coatings. However, the traditional waterproof coatings for NC-3Cs cannot self-heal the inevitable mechanical microcracks suffered during handling and storage, which often gives moisture much more opportunities to destroy the internals. Therefore, it is necessary to develop a self-healing waterproof coating for the protection of NC-3Cs. Herein, a smart self-healing silicone polyurea (SPU) elastomer based on dynamic reversible hydrogen bonds is designed as a waterproof coating for NC-3Cs. The SPU elastomer shows an outstanding self-healing efficiency of 99.06 % after 12-hour self-healing at room temperature. And it also can self-heal its damages even when the ambient temperatures rise to 50 degrees C or drop to -18 degrees C. Moreover, the SPU-coated NC-3C can also self-heal its microcracks in time after being scratched and obtains extremely low water absorptions (<0.20 %) after 24-hour soaking, exhibiting good waterproof performance. Endowing the waterproof coating with self-healing ability is a promising design strategy to repair the coating microcracks and improve the environmental adaptability of NC-3C during handling and storage. This work pioneers a new design of self-healing waterproof coating for NC-3Cs, and it has a positive guiding significance to expend broader application of NC-3C.