P/N/Si-containing hyperbranched polyamide-amine salt with adaptive interfaces: a solution to break the performance paradox in flame-retardant polypropylene

The intrinsic flammability of polypropylene (PP)—a pivotal thermoplastic in automotive engineering—poses a significant safety challenge amid the accelerating shift toward new energy transportation. However, achieving high flame retardancy without compromising mechanical performance remains a critical challenge due to the poor compatibility between non-polar PP and polar flame retardants—a dilemma known as the “performance paradox.” In this study, we report the design of a novel flame retardant, BAPPAM, featuring adaptive interfaces, constructed through the ionic complexation of hyperbranched semi-aromatic polyamide-amine (BA-PAMAM) with phytic acid, followed by sol–gel-based silane encapsulation to yield a phosphorus–nitrogen–silicon hybrid architecture. Benefiting from the synergistic effects among P, N, and Si elements, BAPPAM endows PP composites with outstanding flame retardancy—achieving a limiting oxygen index of 28.5 %, UL-94V-0 rating, and effective suppression of heat release (86 % reduction in peak heat release rate and 69 % decrement in total heat release) and smoke emission (72 % decline in peak smoke production rate and 67 % slippage in total smoke production) at a 20 wt% loading. Remarkably, the adaptive interfaces formed by BAPPAM accommodate mechanical deformation under stress, affording a high elongation at break (up to 453.4 %) comparable to pure PP, along with enhancements of 41.2 % in Young’s modulus (1440 MPa) and 11.2 % in impact strength (3.9 kJ/m 2 ). This work pioneers a novel interfacial engineering strategy that reconciles fire safety with mechanical robustness, offering a solution for the next generation of high-performance, flame-retardant polyolefin composites.