Synergistic flame-retardant effect between lignin and magnesium hydroxide in poly(ethylene-co-vinyl acetate)

Abstract

In this study, we evaluated the interest of combining magnesium hydroxide (MDH) and lignin for developing complementary flame retardant actions in poly(ethylene-co-vinyl acetate) (EVA). Lignin was selected owing to its char forming ability thatwas supposed to reinforce the endothermic effect provided by MDH. The effect of lignin chemical modification by ammonium phosphate functions also evaluated as a way for enhancing its charring effect. Fire properties and thermal behavior of EVA composites were characterized using cone calorimeter, Pyrolysis Combustion Flow Calorimeter (PCFC) and thermogravimetric analysis (TGA). The effect of the incorporation of lignin alone on EVAcomposite thermal and fire behavior first evaluated. Results evidenced that the incorporation of lignin, whatever its nature, induced important reduction of composite thermal stability during TGA analysis as well as significant reduction of the time to ignition (TTI) in cone calorimeter test. However, a significant reduction of peak of heat release rate (pHRR), higher than that obtained with MDH was observed. The combination of lignin and MDH was led to further reduction of pHRR. Furthermore, it was concluded that the chemical modification of lignin is not required prior obtaining improved flame-retardant properties.