Fire safety enhancement of a highly efficient flame retardant poly(phenylphosphoryl phenylenediamine) in biodegradable poly(lactic acid).

Graphical abstract Highlights • A highly-efficient flame retardant PPDA in PLA shows good melt-dripping resistance. • The flame retarded PLA material with only 3 wt% PPDA passes UL-94 V-0 rating. • A small amount of PPDA has little influence on the mechanical properties of PLA. Abstract Flame-retarded poly(lactic acid) (PLA) biodegradable materials are viewed as promising as sustainable alternatives to petroleum-based commodity polymers. A new highly efficient flame retardant, poly(phenylphosphoryl phenylenediamine) (PPDA), was synthesized by the condensation of phenylphosphoryl dichloride with p -phenylenediamine and its structure was confirmed by 1H nulear magnetic resonance and Fourier-transform infrared spectroscopy. When 3 wt% PPDA was incorporated into PLA, the limited oxygen index increased from 20.0% of neat PLA to 25.5% and its UL-94 vertical burning testing achieved V-0 rating. Moreover, the total heat release and peak heat release rate values of PLA/3 wt% PPDA material were decreased from 109.1 MJ/m2 and 643.7 kW/m2 of PLA to 98.3 MJ/m2 and 570.0 kW/m2, respectively, and the fire performance index increased from 0.081 of PLA to 0.132 m2 s/kW. The high fire safety of PPDA in PLA is mainly attributed to the combined effects of the phosphorous-containing radical inhibition and inert gases and the barrier action of the formed char layer. The addition of less than 3 wt% PPDA has little influence on the tensile and impact properties of PLA. The flame retardant PLA blends have great application potential in electrical casing, automobile interiors and three-dimensional printing materials. [ABSTRACT FROM AUTHOR]