A facile surface modification of ammonium polyphosphate with boron-based compound to reduce its particle size and improve the flame retardancy and anti-dripping of polylactic acid resin

Abstract

Polylactic acid (PLA) resin has inherent deficiencies like high flammability and severe melt-dripping, which limit its wide application. To address these issues, a novel APP-based flame retardant (MAPP) with reduced particle size was facilely fabricated by grafting 9, 10-Dihydro −9-oxa −10-phosphaphenanthrene −10-oxide (DOPO) and 4-formylphenylboronic acid (FPBA) onto the surface of raw APP via an ion exchange reaction, achieving a high char yield of 31.3 % in N₂ atmosphere. The synergistic effects of phosphorus-, nitrogen- and boron-containing compounds improved the flame retardancy and anti-dripping performance of PLA/MAPP composites efficiently. Notably, the PLA/6 %MAPP composite exhibited the highest limiting oxygen index (LOI) value of 30.1 % and a UL-94 V-0 rating without melt dripping. Its cone calorimeter results also presented the lowest peak heat release rate (PHRR) and total heat release (THR), which were 19.8 % and 23.2 % lower than those in pure PLA, respectively. The gas- and condensed-phase product analysis revealed combined flame retardancy mechanisms including inert gas dilution, free-radical quenching, catalytic charring, and physical barrier effect. Importantly, the incorporation of MAPP did not significantly compromise the tensile strength (92.0 % of pure PLA) but enhanced the impact strength (31.9 %) of the relating PLA composites. This favorable balance between flame retardancy and mechanical properties in PLA/MAPP composites offers a viable approach to broaden the practical application of PLA.