Simultaneously enhance the fire safety and mechanical properties of PLA by incorporating a cyclophosphazene-based flame retardant

The application of poly(lactic acid) (PLA) has been limited in flame-retardant field, and flame-retardant modification usually deteriorates its mechanical properties. In this study, a reactive flame-retardant hexa(ethylene oxide)-cyclotriphosphazene (HCCP-EP) was synthesized and used to improve the fire retardancy of PLA. As a result, the limiting oxygen index of PLA increased from 19.5% to 27.3% with an addition of 3 wt% HCCP-EP, and the PLA/HCCP-EP blend reached to underwriters laboratories (UL)-94 V-0 rating. The cone calorimeter test results showed that the peak heat release rate and total heat release of PLA decreased by 12.6% and 18.5%, respectively. Interestingly, the tensile strength of PLA increased slightly after the incorporation of HCCP-EP. The improved mechanical properties are ascribed to the fine dispersion of HCCP-EP and the coupling reaction between the epoxy groups of the HCCP-EP and the terminal groups of PLA during the melt processing.