Properties and Mechanism of Flame Retardant Poly(Lactic Acid) Composites Containing Phosphaphenanthrene‐Hydroxyl Phenyl Maleimide Derivative

ABSTRACT A derivative based on 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and maleimide units with terminal hydroxyl group (DH) was synthesized and incorporated in poly(lactic acid) (PLA). The properties and mechanism of PLA/DH composites were investigated. The results showed that PLA composites under 10 wt% DH load achieved vertical combustion test (UL‐94) V‐0 rating with an increased limiting oxygen index (LOI) of 27.2% and a 15.8% decrease in peak heat release rate. The prominent flame retardant efficiency of DH in PLA was attributed to its excellent flame inhibition and diluting effects in gaseous phase as well as a certain cross‐linked structure in the condensed phase. Specifically, the elongation at break of PLA/DH‐7.5 was increased by 17.6% in comparison to that of pure PLA. DH with terminal hydroxyl group displayed enhanced interaction and good compatibility with PLA, thus endowing good comprehensive performances to PLA. As a result, the combination of phosphaphenanthrene and maleimide units with terminal hydroxyl group provides a facile and effective method to improve the flame retardancy and mechanical properties of PLA.