Synergistic flame retardancy and smoke suppression in poly(lactic acid) using phytic-acid-modified alginate and ammonium polyphosphate
Abstract
In this work, an alginate and calcium phytate-based complex (AlgCaPA) was synthesised and applied as a flame-retardant additive for poly(lactic acid) (PLA) in the presence of ammonium polyphosphate (APP) as a co-flame retardant. The total additive content was fixed at 15 mass%, and the ratio between AlgCaPA and APP was systematically optimised. To assess potential synergistic interactions between AlgCaPA and APP, the resulting PLA composites were investigated by thermoanalytical and spectroscopic methods, flammability tests, and mechanical measurements. The composite containing 5 mass% AlgCaPA and 10 mass% APP significantly outperformed PLA containing 15 mass% APP in several aspects; cone calorimetry revealed a 18% reduction in total heat release and a 74% reduction in total smoke production, accompanied by the formation of a substantial char residue. This enhanced flame-retardant performance is attributed to the formation of a compact, thermally stable hybrid char arising from calcium-induced crosslinking of phosphate networks and their integration with a carbonaceous matrix, which effectively enhances barrier properties during combustion.