Amide-based bio-derived flame retardant enhances the fire retardancy, toughness, and UV-aging resistance of polylactic acid

Polylactic acid (PLA) suffers from inherent brittleness, flammability, and poor UV resistance, which significantly limit its practical applications. Conventional additives often exhibit single functionality and tend to reduce the crystallinity of polymers, leading to a deterioration in mechanical properties. In this study, a multifunctional bio-based additive (HVB) was synthesized by introducing amide groups into vanillin-modified hexachlorocyclotriphosphazene. The molecular interactions formed between the amide groups in HVB and PLA further promoted the enhancement of PLA crystallinity. Consequently, both the tensile strength and elongation at break of PLA were remarkably improved. When the HVB loading was 3 wt%, the composite exhibited a 3.4% increase in tensile strength and a 75.8% improvement in elongation at break, while achieving a UL-94 V-0 flame-retardant rating. Furthermore, molecular simulations combined with experimental characterizations were employed to elucidate the carbonization and free-radical-trapping mechanisms of the flame retardant.