Synthesis of aluminum bis(hydroxy-phenyl-methyl)phosphinate and its synergistic flame retardant mechanism in PLA

In this paper, we report on the synthesis of a new aluminum bis(hydroxy-phenyl-methyl)phosphinate, AlBPi, under mild reaction conditions. The product structure was confirmed via characterization, and its thermal stability and flame retardant properties were assessed. To improve the flame retardant properties, we employed ammonium polyphosphate (APP) as a synergist with AlBPi. The PLA composite material containing 10% AlBPi and 5% APP achieved an LOI of 28.1% and a UL-94 rating of V-1. Cone calorimetry tests showed a significant reduction in PHRR, THR, PSPR, and TSP for the PLA/AlBPi/APP composite compared to the pure and PLA/AlBPi materials. SEM analysis revealed a continuous and dense char layer on the residual surface of the synergistic flame retardant sample. AlBPi and APP exhibited excellent synergistic flame retardant effects, with both releasing a large amount of PO·free radicals. APP was also able to release inert gas, exhibiting excellent flame retardant effects in the gas phase. Additionally, APP improved the charring performance of AlBPi and formed a compact char layer on the material surface, achieving good flame retardant effects in the condensed phase. Therefore, the AlBPi and APP synergistic flame retardant system can be considered a viable flame retardant additive for PLA.

Highlights

• A novel flame retardant AlBPi was synthesized.
• AlBPi and APP demonstrate good synergistic flame retardant performance in PLA.
• AlBPi and APP play a flame retardant role in both gas and condensed phases.