Inorganic phase network modulates combustion behavior and electrical properties of an intumescent flame-retardant coating for reliable cable tapes

Surface treatment of cable tapes with a flame-retardant coating is critical for maintaining operational stability during fire incidents. While intumescent flame retardants (IFRs) effectively inhibit flame propagation and can even achieve self-extinguishment, the resulting char often exhibits high electrical conductivity, posing a risk of electrical breakdown in fire scenarios. To address this issue, we utilize waste oyster shell (OS), composed of laminar CaCO 3 , to construct a continuous inorganic phase network within the IFR matrix. This strategy enables a more controlled and uniform combustion process. Cone calorimetry tests demonstrate significant improvements, including a 49.3 % reduction in peak heat release rate and a 64.9 % decrease in total smoke production rate. The optimized combustion process and phase change of CaCO 3 eventually lead to the formation of the highly expanded carbon/Ca(PO 3 ) 2 hybrid network, thereafter effectively breaking the connectivity of conductive carbon in the char. The degree of expansion increases from 146.7 % (pristine IFRs) to 341.9 % (OS-modified IFRs) and surface resistivity remarkably elevates by 1715.4 %, substantially mitigating electrical hazards. Comprehensive analyses including TG–IR, SEM, Raman, and XPS elucidate the synergy between gas-phase and condensed-phase flame-retardant mechanisms. In summary, this study underscores the pivotal role of inorganic phase networks in modulating the combustion behavior of IFRs and their resultant electrical properties, providing a viable pathway for designing next-generation cables with superior fire safety performance.