Improving Flame‐Retardant Properties of Poly (Lactic Acid) Composites Using Maleic Anhydride‐Modified <scp>DOPO</scp> and <scp>SiO₂</scp>

ABSTRACT Polylactic acid (PLA) is well regarded for its excellent environmental friendliness; however, its flammability presents a significant barrier to wider applications. Developing highly flame‐retardant PLA (with a limiting oxygen index, LOI, greater than 30%) using simple, general methods remains a challenge. In this study, maleic anhydride (MA) was used to modify 9,10‐dihydro‐9‐oxa‐10‐oxide (DOPO), enhancing its thermal stability and interaction with the PLA matrix. Additionally, by leveraging the carbonization effect of nano‐SiO 2 , DOPO‐MA was compounded with nanosilica to further improve PLA's flame‐retardant properties. As a result, a highly flame‐retardant PLA with an LOI of 31.3% and a UL‐94 V‐0 rating was successfully prepared using 5 wt.% DOPO‐MA and 3 wt.% SiO 2 . Furthermore, total heat release (THR) and peak heat release rates (pHRR) of PLA decreased by 7% and 25%, respectively. Detailed analysis of the flame‐retardant mechanism revealed that nano‐SiO 2 significantly increased the residual char content and promoted the formation of a more stable graphite carbon structure. Moreover, silica effectively suppressed the generation of combustible gases in the pyrolysis products of PLA, collectively enhancing its flame‐retardant properties. This study presents a straightforward and scalable approach for designing highly efficient phosphorus/silica‐containing synergistic flame retardants, offering valuable insights into PLA flame retardancy.