Novel Si-MXene/PAPP Hybrid System for High-Performance Flame-Retardant Polypropylene Composites

s The development of high-performance flame-retardant polypropylene (PP) composites is essential for enhancing fire safety across various industries. However, conventional intumescent flame retardant systems often suffer from poor char stability, weak condensed-phase protection, and insufficient gas-phase flame inhibition. To address these challenges, this study introduces a synergistic system combining Si-modified MXene (Si-MXene) and piperazine-modified ammonium polyphosphate (PAPP) to enhance the flame retardancy of PP composites. The piperazine modification of PAPP improves its compatibility with PP, facilitating uniform dispersion and enhancing its catalytic charring capability. Simultaneously, Si-modified MXene reinforces the char layer by promoting the formation of a highly graphitized and compact carbon structure, effectively blocking heat and oxygen transfer. As a result, the Si-MXene/PAPP system significantly reduces the peak heat release rate (PHRR) of PP by 52.6% and total heat release (THR) by 35.4%, while substantially improving thermal stability and char quality. Moreover, gas-phase analysis confirms that phosphorus radicals (P·, PO·) and non-flammable gases (NH₃, H₂O) scavenge combustion free radicals and dilute flammable volatiles, effectively suppressing flame propagation. This study provides a novel approach to de veloping high-efficiency flame-retardant PP composites, offering new insights into the synergistic mechanisms of MXene-based hybrid flame retardants and advancing the design of eco-friendly, high-performance polymeric materials for safety-critical applications.