Fully bio-based flame retardancy in polyhydroxyalkanoates: Sustainable engineering through phytic acid-derived additives

Polyhydroxyalkanoates (PHA), a class of renewable and biodegradable polymers, show significant potential for fire-sensitive applications but face limitations due to conventional flame-retardant approaches that depend on non-renewable additives and energy-intensive processes. Here, we present a sustainable flame-retardant system engineered via a one-pot synthesis of phytate derivatives (PA 1 PEA 6 and PA 1 PEA 12 ) from plant-derived phytic acid and phenethylamine. Incorporating 10 wt% PA 1 PEA 12 into PHA achieved exceptional fire safety performance while preserving material integrity, evidenced by a 51 % enhancement in limiting oxygen index (29.7 %), UL-94 V-0 certification, and 91.9 % retention of original impact strength. Advanced multiscale analyses (SEM-EDS, FTIR, TG-IR) revealed a condensed-phase dominant mechanism: polyphosphate derivatives catalyzed the formation of a coherent char barrier during combustion, effectively blocking oxygen permeation and heat propagation (18.6 % reduction in peak heat release rate). Concurrently, this system suppressed volatile organic emissions, reducing total smoke production by 22 %. The bio-based additive design not only aligns with circular economy principles but also establishes a scalable paradigm for balancing flame retardancy with mechanical and environmental performance in biodegradable polymers, significantly expanding PHA's applicability in eco-conscious material engineering.