Eco-friendly flame retardant poly(lactic acid) composites based on banana peel powders and phytic acid: flame retardancy and thermal property

A novel bio-flame retardant (PA-B) was prepared based on green materials--banana peel powder (BPP) and phytic acid (PA), then PA-B was used to prepare flame retardant poly(lactic acid) (PLA) composites. The flame retardancy and thermal property of PLA composites were studied. It can be found that the limiting oxygen index (LOI) of PLA composite with 15.0 wt% BPP is 22.1%, showing the heavy dripping during the combustion and failing to reach the vertical burning tests (UL-94) V-0 rating. However, when 15.0 wt% PA-B is added, the LOI is significantly increased to 37.5%, and the composite can reach UL-94 V-0 rating with the dripping problem is obviously reduced. Furthermore, PA-B is helpful to ameliorate the thermal property of PLA composites under the high temperature. The char residue of PLA/PA-B15 is 10.9 wt% at 550.0 °C, showing much higher value than that of PLA/B15 (3.3 wt%) and pure PLA (almost nothing left). From flammability analysis, PA-B not only is a crucial part of promoting the formation of char layer with high quality in the solid phase, which can play a “barrier effect” role to protect the underlying matrix and retard combustion process, but also has the flame retardant effect in the gaseous phase on the basis of PO· free radical. This work provides an efficient way to prepare bio-based flame retardant PLA composites, and also offers a new method to reuse agricultural wastes like banana peel.