Expanding the Frontiers of Flame-Retardant Hydrogels: Recent Advances in Applications, Design Strategies, and Multifunctional Performance

Flame-retardant hydrogels are multifunctional materials that offer fire resistance, mechanical flexibility, self-adhesion, water retention, and self-healing properties. This review discusses recent developments in these materials, categorizing them into two types: coatings and bulk materials. Coating-type hydrogels provide fire protection for the surfaces of various materials, including coal, foam, wood, textiles, and safety gear. In contrast, bulk hydrogels possess flame-retardant properties suitable for applications in robotics, 3D printing, sensors, and energy storage. Moreover, this review highlights recent advancements in various design strategies for flame-retardant hydrogels, including their synthesis methods, mechanisms, formulations, and performance indicators. The synthesis techniques include physical, covalent, and dynamic crosslinking, allowing diverse network architectures. Flame-retardant mechanisms involve heat absorption, gas-phase dilution, char formation, intumescence, and radical quenching. The formulations typically incorporate additives such as polymers, phosphorus compounds, inorganic fillers, and nanomaterials. Key performance indicators assess both flame-retardant and non-flame-retardant functionalities, essential for advanced applications of flame-retardant hydrogels. Specifically, this review explores the multifunctional capabilities of flame-retardant hydrogels and compares these findings with previous studies, emphasizing their potential to broaden applications across various fields. The review concludes by offering valuable insights into future directions for the development of flame-retardant hydrogels in next-generation fire-safe technologies.