Metal-polyphenol networks functionalized Mg2B2O5 whiskers for multifunctional intumescent flame-retardant polypropylene composites

Polypropylene (PP) is a widely used commodity thermoplastic in electronics, automotive and new energy applications, yet its inherent flammability, severe melt dripping, toxic smoke emission and unsatisfactory functional compatibility greatly limit its use in high-performance engineering scenarios. Herein, a core-shell flame-retardant synergist (MB@TA-Ni) was fabricated by in-situ assembly of bio-based tannic acid-nickel (TA-Ni) nanoparticles on Mg 2 B 2 O 5 whiskers (MB), and incorporated into piperazine pyrophosphate (PAPP)-based intumescent flame-retardant PP to prepare high-performance multifunctional nanocomposites. With a total flame-retardant loading of 22 wt%, replacing only 1 wt% PAPP with MB@TA-Ni raised the limiting oxygen index (LOI) of the composite to 33.2%, achieved a UL-94 V-0 rating with full suppression of melt dripping, and reduced the peak heat release rate (PHRR), peak smoke production rate (PSPR) and peak CO production rate (PCOPR) by 72.4%, 84.7% and 70.0%, respectively, compared to neat PP. The fire performance index (FPI) was enhanced by 3.1 times and the fire growth index (FGI) decreased by 97.4%, indicating significantly mitigated fire hazards. Moreover, the composite exhibited an 89.0% increment in unnotched impact strength, realizing the simultaneous integration of exceptional flame retardancy, anti-dripping, smoke suppression and mechanical robustness. The underlying synergistic mechanism is elucidated, whereby MB@TA-Ni reinforces the intumescent char barrier and catalyzes char graphitization in the condensed phase, while PAPP quenches reactive free radicals to terminate combustion chain reactions in the gas phase. This work provides a facile yet efficient strategy for developing multifunctional fire-safe polyolefin composites, which hold great application promise in high fire-risk engineering fields.