Lignin-derived PFAS- and halogen-free flame retardant with robust thermal stability for PC/ABS blends

The flammability of polycarbonate/acrylonitrile butadiene styrene (PC/ABS) significantly restricts its use in safety-critical applications, despite its desirable mechanical and thermal properties. Bio-based, halogen- and PFAS-free flame retardants have gained interest as sustainable alternatives to conventional halogen-based flame retardants for engineering thermoplastics, yet most exhibit insufficient thermal stability for the demanding processing temperatures (>250 °C) required by high melting point engineering thermoplastics, such as PC/ABS. To overcome this fundamental thermal stability bottleneck, in this study, a reactive compatibilization strategy was developed to tailor a thermally robust and compatibilized lignin-derived flame-retardant system for PC/ABS. Nitrogen and phosphorous modified lignin was pre-compounded with styrene-maleic anhydride copolymer (SMA), which not only significantly raised the onset decomposition temperature ( T d5 = 293 °C) to withstand the high-temperature compounding, but also ensured uniform dispersion within PC/ABS. This strategy enabled, to the best of our knowledge, for the first time, effective incorporation of a bio-based flame retardant into engineering-grade PC/ABS at industrial relevant loadings. With the addition of 5 wt% LNP and 10 wt% SMA, the PC/ABS blends achieved the UL-94 V-0 rating with an increased limited oxygen index (LOI) and a 51.5 % reduction in peak heat release rate, while significantly enhancing heat deflection temperature and maintaining tensile strength of the PC/ABS samples. Mechanistic investigations revealed a synergistic condensed-phase barrier effect from crosslinked phosphorus-rich char and a gas-phase radical-quenching effect to suppress flame propagation. This work aligns with current regulatory drivers to replace halogenated and PFAS-based additives, showing a viable pathway for developing sustainable and high-performance flame retardants for engineering thermoplastics with high melting temperatures. • Incorporation of a bio-based FR into high melt temperature thermoplastics • SMA enhances both thermal stability and compatibility of lignin FR in PC/ABS. • UL-94 V-0 achieved at 5 wt% lignin FR with superior efficiency over previous systems. • Mechanical strength and heat deflection temperature improved in PC/ABS materials.