A bio-based flame retardant with super-low addition for polylactic acid: Simultaneous enhancement of flame retardancy, smoke suppression, and biodegradability

The development of biodegradable polymers that simultaneously exhibit flame retardancy and smoke suppression remains a significant challenge. In this work, a bio-based flame retardant (PA-AB) was synthesized from phytic acid (PA) and 2-aminobenzimidazole (AB) via a facile one-step reaction and incorporated into polylactic acid (PLA) by melt blending. At a low loading of 1.0 wt%, PA-AB enabled PLA to achieve a UL-94 V-0 rating with a limiting oxygen index of 26.5 % and effectively suppressed melt dripping. Cone calorimetry results showed that PLA/PA-AB-1.0 exhibited a prolonged ignition time, a slight reduction in heat release, and a pronounced decrease in total smoke release (89.3 %) compared with neat PLA, demonstrating the combined flame-retardant and smoke-suppressing effects of PA-AB. Mechanistic analysis suggests that PA-AB predominantly acts in the gas phase, with a limited contribution in the condensed phase. In addition, PA-AB enhanced the ultraviolet-shielding capability of PLA without significantly compromising optical transparency. Mechanical testing revealed that PLA/PA-AB-1.0 retained 73 % of the tensile strength and 87 % of the elongation at break of neat PLA. Enzymatic degradation studies further indicated that PA-AB accelerated the degradation behavior of PLA. This study provides an effective approach for designing multifunctional, bio-based flame-retardant PLA materials.