A new direction in design of bio-based flame retardants for poly(lactic acid)

A novel bio-based nitrogen-rich and phosphorus-rich flame retardant (Phyt/PEI-TA) was synthesized and characterized by Fourier transform infrared, inductively coupled plasma, and thermogravimetric analysis (TGA). Thermal degradation and flame retardant properties of poly(lactic acid) (PLA) containing 20 wt% Phyt/PEI-TA were investigated by TGA, cone calorimetry, and microcalorimeter of combustion (pyrolysis combustion flow calorimeter) measurements. Thermogravimetric analysis results showed that introduction of newly developed Phyt/PEI-TA to PLA significantly improved its thermal stability, as signaled by much more amount of PLA char formed compared to the reference sample. Surprisingly, the use of Phyt/PEI-TA did not decrease the onset degradation temperature of PLA. In agreement with TGA results, the cone calorimetry results approved excellent flame retardancy of PLA upon addition of Phyt/PEI-TA (36% reduction in peak of heat release rate compared to that of neat PLA). Based on the analysis performed on the remainder of char after cone calorimeter test as well as analyses on heat release rate curves, the condensed phase action by promoting the formation of char was identified as principal impact of the Phyt/PEI-TA on flame retardancy of PLA. Finally, the performance of developed bio-based flame retardant was compared with more than 60 flame retardant systems previously reported in the literature.