A THEIC-based polyphosphate melamine intumescent flame retardant and its flame retardancy properties for polylactide

•PLA/APP/TPM composite has excellent flame retardancy and anti-dripping capability.•PLA with 25 wt% APP/TPM(0.5:1) can acquire LOI value of 36.5% and achieve UL-94 V-0 rating with no melt dripping.•TPM can effectively improve thermal stability of PLA at higher temperature.•The richness of P-O-C structure in TPM can accelerate the process of char formation.

A macromolecular intumescent flame retardant tris(2-hydroxyethyl) isocyanurate polyphosphate melamine (TPM) was synthesized, its structure was confirmed by Fourier transform infrared spectroscopy (FTIR), 1H and 31P nuclear magnetic resonances (NMR). The flame retardancy and combustion properties of PLA/TPM composites were evaluated by limiting oxygen index (LOI), UL-94, and cone calorimetry tests. It was found that PLA with 25 wt% APP/TPM (0.5:1) acquired LOI 36.5% and achieved UL-94 V-0 rating with no melt dripping. Cone calorimetry tests showed that pHRR and THR of PLA/TPM composites were dramatically reduced compared with that of pure PLA, the HRR curve suggested that TPM could accelerate char forming process. TGA demonstrated that TPM effectively improved thermal stability of PLA. The possible thermal degradation mechanism, structure and morphology of char layer were studied by FTIR, XPS and SEM.