Atom-economic synthesis of an oligomeric P/N-containing fire retardant towards fire-retarding and mechanically robust polylactide biocomposites.

• Atom-economic synthetic strategy of a P/N fire retardant (APN) is developed. • 3 wt% APN significantly improves the fire safety of PLA. • The toughness of PLA increases by 85% but maintaining its tensile strength. Renewable and biodegradable polylactide (PLA) has excellent mechanical strength but is highly flammable which restricts its practical applications. Many phosphorus/nitrogen (P/N)-based flame retardants are effective in PLA, but their high addition loading usually decreases the mechanical strength of the PLA bulk. For polyphosphoramides, despite high fire-retardant efficiency, their chemical synthesis often generates chemical wastes as byproducts. Herein, we report an atom-economic and highly efficient oligomeric P/N fire retardant (APN) prepared using a mild Michael addition polymerization with no byproducts. Using only 3 wt% APN, the resulting PLA exhibits desired fire retardancy including a UL-94 V-0 rating and a limiting oxygen index of 37.6%. Furthermore, the toughness of the fire-retardant PLA increases by 85% compared to pure PLA, with both tensile strength and thermal stability preserved. This work offers an atom-economic strategy for synthesizing highly efficient P/N fire retardants for use in the creation of fire-resistant PLA with robust mechanical properties. Atom-economic synthesis was developed to synthesizing a P/N-containing fire retardant for creating fire-retardant PLA. [Display omitted] [ABSTRACT FROM AUTHOR]