Mechanically flexible and flame retardant polyphenol-bridged casein/MXene composite for fire proofing repeatable contact/non-contact fire monitoring

Early fire warning sensors are critically vital to avoid the potential fire accidents for preventing huge life and economic losses, however, currently available fire warning materials work only under direct fire/smoke exposure or relatively high temperature with poor sensitivity. Herein, a biobased durable, reusable and highly sensitive fire warning composite (CTM) was developed using casein as the film-forming agent and dopant, MXene (Ti3C2Tx) as the conductive skeleton, and tannic acid as the crosslinking agent and free radical scavenger. Notably, the resultant CTM composite exhibits mechanically flexible properties, excellent thermal stability (T10% of 239.6 °C) and superb fire safety (total heat release (THR), total smoke production (TSP) and CO production rate of sensor are only 1.35 MJ/m2, 0.19 m2 and 0.42 mg/s, respectively). More importantly, the CTM presents reliable and rapid cycle warning responses under both direct flame attack and non-contact fire threat. Under continuous exposure to flame, it demonstrates an ultra-fast response time (982 ms), a long-time stable alert (93 s), and a repeatable warning ability. Under the impact of repetitively approaching flame, it exhibits consistent distance-dependent changes in resistance within 3 s, affording attractive accessibility to detect flame position. Moreover, this CTM composite can easily be coated on flexible textiles to develop a large-scale wireless real-time fire alarming system that can deliver the monitored signal to remote sites within only 3 s, thus it provides a potential application prospect in constructing smart fire-safe buildings.