Combined Effect of Bridged 9,10‐Dihydro‐9‐Oxa‐10‐Phosphaphenanthrene‐10‐Oxide Derivatives and Cellulose on the Flame Retardancy and Thermal Decomposition of Poly(Butylene Adipate‐Co‐Terephthalate)

ABSTRACT The potential applications of poly(butylene adipate‐co‐terephthalate) (PBAT), a rapidly developing biodegradable polymer, are severely hindered owing to its poor flame retardancy. In this study, we investigated the influence of combining a 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO)‐derived compound (PN‐DOPO) with microcrystalline cellulose (MCC) on the flame retardancy and thermal decomposition of PBAT. The results demonstrated that the PBAT composites, specifically PBAT/15% PN‐DOPO/5% MCC, not only attained a UL‐94 V‐0 classification but also registered the highest limiting oxygen index value of 30.2%, with a 47.4% reduction in peak heat release rate (p‐HRR) and a 55.0% decrease in total heat release (THR) compared with unmodified PBAT. The superior flame retardance is primarily attributed to the extinguishing effect of phosphorus‐rich free radicals and the dilution of noncombustible gas in the gas phase, and the continuous char layer acting as a barrier in the condensed phase. A possible flame‐retardant mechanism for the PBAT/PN‐DOPO/MCC composites is proposed. This study provides a basis for future research on high‐performance flame‐retardant PBAT composites.