A flexible film sensor based on sodium alginate/silk nanofiber for real-time monitoring of the ambient temperature and personnel respiration in flame environment

Natural polymers are considered powerful candidate for preparing a new generation of intelligent sensors, however, their application in fire environment is limited restricted by the low flame retardancy and thermal stability. Herein, we developed a novel flexible film (SSGP) entirely composed of bio-mass, namely natural silk nanofibers, sodium alginate and phytic acid, via solution casting and self-assembly strategy. It exhibited reliable tensile properties (11.01 MPa), high flame retardancy (LOI reached 38 %), and thermal stability. Specifically, SSGP not only showed sensitive and reversible response at different temperatures (50-125 °C) with a GF of 10.8, but also triggered warning within 2.2 s of being exposed to a flame without being incinerated. Moreover, SSGP responded to humidity changes in the environment (22-94 % RH) and could be used for respiratory monitoring, with a response/recovery time of only 0.76 s/1.01 s. Additionally, SSGP based on natural polymers retain degradability (39.8 % within 30 days). Thus, SSGP had the potential to be integrated as a core component into sensor for real-time monitoring of ambient temperature and respiration of personnel in steelworks, fire rescue, battlefield and other flame environment. This study may provide new insights into the application of natural polymers in the flexible multifunctional sensor.