Polymerization of hydroxylated graphitic carbon nitride as an efficient flame retardant for epoxy resins

Graphitic carbon nitride (GCN) has been recognized as a potential flame retardant (FR) due to its high thermal stability and nitrogen richness. Previous work has been limited to hybridization without involving covalent modification. Here, we developed a facile covalent modification approach to polycondensation that can chelate with metal ions (PCNOH–CuCo) from GCN. Structural and mechanical property characterization confirmed the ability of PCNOH–CuCo to be uniformly dispersed in the epoxy resin (EP). Fire tests showed excellent fire resistance of EP with 10 wt% PCNOH–CuCo (EP/10PCNOH–CuCo), including a limiting oxygen index of EP/10PCNOH–CuCo up to 31.5%, and the reduction in the peak heat release rate, total heat release, peak smoke production, total smoke production peak CO production, and peak CO₂ production of 47.9%, 37.5%, 20%, 44.5%, 30.9%, and 42.5%, respectively. This work provides a solution for the fabrication of GCN-based FRs and their derived metal-doped FRs.