Tough and flame-retardant poly(lactic acid) composites prepared via reactive blending with biobased ammonium phytate and in situ formed crosslinked polyurethane

Abstract Simultaneously endowing poly(lactic acid) (PLA) with flame retardancy and toughness still is a challenge. In this study, a novel biobased phosphorus-nitrogen containing flame retardant (PA-HDA), synthesized from phytic acid and 1,6-hexanediamine, is employed into a toughened PLA (TPLA) composite, which is achieved by in situ formed crosslinked polyurethane (CPU). The comprehensive properties of PLA composites such as thermal stability, thermal transition behaviors, mechanical properties and flame retardancy have been well investigated. Only with 5 wt% PA-HDA loading, TPLA can pass UL-94 V-0 rating while its limiting oxygen index (LOI) value is as high as 26%. Besides, the flame retardant TPLA still keeps good tensile and impact toughness, i.e. its elongation at break and notched impact strength are enhanced to 207.3% and 5.0 kJ/m2 , which are 26.6 and 2.8 times of those of neat PLA, respectively. Surprisingly, it is found that PA-HDA can rise the crystallinity of PLA. But the glass transition temperatures and the initial decomposition temperatures of flame-retardant TPLA are decreased compared to those of pure PLA. By adjusting the PA-HDA loading, we can achieve the balance between the flame retardancy and good mechanical properties of PLA.