Enhancing flame retardancy of poly(lactic acid) with a novel fully biobased flame retardant synthesized from phytic acid and cytosine

Abstract In order to reduce environmental pollution and improve material safety, biobased flame‐retardant polymers are gradually becoming a new trend. We synthesized a fully biobased flame retardant called PACY by reacting phytic acid (PA) and cytosine (CY) in water, and then mixed the flame retardant with biodegradable poly(lactic acid) (PLA) to obtain composites, characterizing the performance of the composites by microscopic morphology, thermal properties, flame‐retardant performance and so on. The test results showed that the PLA composite with 2 wt% PACY (PLA/2PACY) achieved UL‐94V‐1 and the PLA composite with 4 wt% PACY (PLA/4PACY) had a limiting oxygen index of 23.6%. Compared to pure PLA, PLA/4PACY had good flame retardancy with 12% less peak heat release and 19% less total heat release. Analysis of the flame‐retardant mechanism showed that PACY could promote the formation of a graphitized carbon layer after burning PLA, therefore enhancing the flame‐retardant properties of PLA. Through a thermal stability study, it was found that the temperature required for PACY mass loss of 5% was 275 °C and the residual weight reached 38% at 750 °C, which indicated high thermal stability and residual carbon rate. The addition of PACY also improved the thermal conductivity of PLA, with that of PLA/4PACY being 3.84 times higher than that of pure PLA. In addition, the tensile strength, flexural modulus, maximum force during impact and maximum energy received during fracture of PLA/4PACY increased by 3.3%, 8.1%, 29.2% and 17.5% respectively over pure PLA, effectively improving the mechanical properties of PLA. Overall, a fully biobased flame retardant was synthesized for improving the fire resistance of PLA degradable polymers. © 2023 Society of Industrial Chemistry.