Synergistic Flame Retardancy in SBS / IFR Composites: Role of OMMT / MoO 3 Hybrid System Explored via Real‐Time Char Resistance Monitoring

ABSTRACT Both molybdenum trioxide (MoO 3 ) and organo‐modified montmorillonite (OMMT) serve as synergists in intumescent flame‐retardant (IFR) systems, yet their distinct mechanisms complicate elucidation of their combined effects. In this study, an styrene–butadiene–styrene (SBS)/IFR composite containing OMMT/MoO 3 was developed, and real‐time electrical resistance monitoring of the char layer was used to investigate the synergistic flame‐retardant mechanism. Results showed that combining OMMT and MoO 3 enhanced flame retardancy and char stability, with 2 wt% OMMT achieving the best performance (UL‐94V‐0). Thermogravimetric analysis (TGA) revealed that the OMMT/MoO 3 system lowered the initial decomposition temperature of the IFR, promoting early char formation. Fourier transform infrared spectroscopy (FTIR) and x‐ray photoelectron spectroscopy (XPS) confirmed that OMMT facilitated the early decomposition of ammonium polyphosphate (APP), increased char viscosity, and contributed to denser, more stable char structures. Scanning electron microscopy (SEM) and resistance monitoring demonstrated that suitable OMMT content promoted the formation of a continuous, compact char layer. However, excessive OMMT induced over‐catalysis, generating excess gases during early combustion, which ruptured the char and formed pores, ultimately reducing flame retardancy.