Fire alarm nano-coating with the controlled release of phosphorus-containing free radical for considerable flame retardant performance

Abstract

The colloidal properties and surface charge characteristics of graphene oxide (GO) often lead to flocculation during the layer-by-layer (LBL) assembly. Innovatively, the charged flame retardant molecule, amino-tris(methylene phosphonic acid) (ATMP), is encapsulated within the inner cavity of halloysite nanotubes (HNTs). This integration exploits the unique structural features of HNT's inner cavity and outer wall. A composite nano-coating is constructed on the three-dimensional skeletal structure of melamine foam (MF) by assemblying GO with HNT-ATMP. This composite nano-coating exhibits both condensed-phase and gas-phase flame retardant functions. During the thermal decomposition process, phosphorus-containing radicals released from the HNTs' inner cavities enhance the flame retardancy. Moreover, the composite nano-coating demonstrates sensitive fire warning performance. A composite MF coated with 10 layers of this nano-coating emits a warning signal within 8 s fire exposure and maintains this signal without circuit failure. This study elucidates the mechanisms of flame retardancy and fire warning based on the thermal decomposition process and char layer analysis. By addressing the issue of GO flocculation during the assembly process, this research not only clarifies the underlying flame retardant and fire warning mechanisms of composite nano-coating but also proposes solutions for prolonging the duration of fire warning signals in advanced materials.