Effects of hexa (ethyl lactate)-cyclotriphosphazene on flame retardancy and mechanical properties of polylactic acid

Using biobased additives to improve the performance of polylactide (PLA) is important for maintaining its sustainability. In this work, an eco-benign flame retardant HELCP was synthesized by reacting ethyl lactate with cyclotriphosphazene. The HELCP was used to modify the flame retardancy of PLA. A small amount of 5.0 wt% HELCP endows PLA with a UL-94 V0 rating and a limiting oxygen index of 25.3 vol%. The mechanical properties and transparency of PLA/HELCP blends is almost the same as neat PLA. Moreover, the molecular weight of PLA blends does not decrease but increase instead. The phosphazene group of HELCP plays an important role in gas phase and the plasticization of HELCP shows a certain melting-away effect which is the flame-retardant mode of action in this system. The ethyl lactate part of HELCP undergoes ester exchange reactions with PLA and improves the compatibility between PLA and HELCP. This work provides a novel method for preparing PLA blends with good flame retardancy and mechanical properties.